[v2,2/5] iio: Introduce the generic counter interface

Commit Message

William Breathitt Gray Sept. 25, 2017, 6:08 p.m. UTC

This patch introduces the IIO generic counter interface for supporting
counter devices. The generic counter interface serves as a catch-all to
enable rudimentary support for devices that qualify as counters. More
specific and apt counter interfaces may be developed on top of the
generic counter interface, and those interfaces should be used by
drivers when possible rather than the generic counter interface.

In the context of the IIO generic counter interface, a counter is
defined as a device that reports one or more "counter values" based on
the state changes of one or more "counter signals" as evaluated by a
defined "counter function."

The IIO generic counter interface piggybacks off of the IIO core. This
is primarily used to leverage the existing sysfs setup: the IIO_COUNT
channel attributes represent the "counter value," while the IIO_SIGNAL
channel attributes represent the "counter signal;" auxilary IIO_COUNT
attributes represent the "counter signal" connections and their
respective state change configurations which trigger an associated
"counter function" evaluation.

The iio_counter_ops structure serves as a container for driver callbacks
to communicate with the device; function callbacks are provided to read
and write various "counter signals" and "counter values," and set and
get the "trigger mode" and "function mode" for various "counter signals"
and "counter values" respectively.

To support a counter device, a driver must first allocate the available
"counter signals" via iio_counter_signal structures. These "counter
signals" should be stored as an array and set to the init_signals member
of an allocated iio_counter structure before the counter is registered.

"Counter values" may be allocated via iio_counter_value structures, and
respective "counter signal" associations made via iio_counter_trigger
structures. Initial associated iio_counter_trigger structures may be
stored as an array and set to the the init_triggers member of the
respective iio_counter_value structure. These iio_counter_value
structures may be set to the init_values member of an allocated
iio_counter structure before the counter is registered if so desired.

A counter device is registered to the system by passing the respective
initialized iio_counter structure to the iio_counter_register function;
similarly, the iio_counter_unregister function unregisters the
respective counter.

Signed-off-by: William Breathitt Gray <[e-mail]>
---
 MAINTAINERS                        |    7 +
 drivers/iio/Kconfig                |    8 +
 drivers/iio/Makefile               |    1 +
 drivers/iio/counter/Kconfig        |    1 +
 drivers/iio/industrialio-counter.c | 1151 ++++++++++++++++++++++++++++++++++++
 include/linux/iio/counter.h        |  221 +++++++
 6 files changed, 1389 insertions(+)
 create mode 100644 drivers/iio/industrialio-counter.c
 create mode 100644 include/linux/iio/counter.h

Comments

Benjamin Gaignard Sept. 29, 2017, 1:42 p.m. UTC | #1

2017-09-25 20:08 GMT+02:00 William Breathitt Gray <[e-mail]>:
> This patch introduces the IIO generic counter interface for supporting
> counter devices. The generic counter interface serves as a catch-all to
> enable rudimentary support for devices that qualify as counters. More
> specific and apt counter interfaces may be developed on top of the
> generic counter interface, and those interfaces should be used by
> drivers when possible rather than the generic counter interface.
>
> In the context of the IIO generic counter interface, a counter is
> defined as a device that reports one or more "counter values" based on
> the state changes of one or more "counter signals" as evaluated by a
> defined "counter function."
>
> The IIO generic counter interface piggybacks off of the IIO core. This
> is primarily used to leverage the existing sysfs setup: the IIO_COUNT
> channel attributes represent the "counter value," while the IIO_SIGNAL
> channel attributes represent the "counter signal;" auxilary IIO_COUNT
> attributes represent the "counter signal" connections and their
> respective state change configurations which trigger an associated
> "counter function" evaluation.
>
> The iio_counter_ops structure serves as a container for driver callbacks
> to communicate with the device; function callbacks are provided to read
> and write various "counter signals" and "counter values," and set and
> get the "trigger mode" and "function mode" for various "counter signals"
> and "counter values" respectively.
>
> To support a counter device, a driver must first allocate the available
> "counter signals" via iio_counter_signal structures. These "counter
> signals" should be stored as an array and set to the init_signals member
> of an allocated iio_counter structure before the counter is registered.
>
> "Counter values" may be allocated via iio_counter_value structures, and
> respective "counter signal" associations made via iio_counter_trigger
> structures. Initial associated iio_counter_trigger structures may be
> stored as an array and set to the the init_triggers member of the
> respective iio_counter_value structure. These iio_counter_value
> structures may be set to the init_values member of an allocated
> iio_counter structure before the counter is registered if so desired.
>
> A counter device is registered to the system by passing the respective
> initialized iio_counter structure to the iio_counter_register function;
> similarly, the iio_counter_unregister function unregisters the
> respective counter.
>
> Signed-off-by: William Breathitt Gray <[e-mail]>

Hi William,

Thanks for your patches, I start try to implement them in stm32-timer driver
but I think it will take me some time before understand all your code.

I have some warning when compiling the code (see below).

About wording, I think that using "trigger" to describe signal active
states/edges
could be confusing in IIO context but I haven't found yet a better name.

I also not very sure about what you expect from iio_counter_ops signal_read and
signal_write functions, do you think get/set the value of the signal ?
(i.e read gpio level ?)

I will continue to review and implement your patches, I hope that end
of next week
have something functionnal to share with you.

Thansk to have propose this, I do believe it will be helpful

Benjamin
> ---
>  MAINTAINERS                        |    7 +
>  drivers/iio/Kconfig                |    8 +
>  drivers/iio/Makefile               |    1 +
>  drivers/iio/counter/Kconfig        |    1 +
>  drivers/iio/industrialio-counter.c | 1151 ++++++++++++++++++++++++++++++++++++
>  include/linux/iio/counter.h        |  221 +++++++
>  6 files changed, 1389 insertions(+)
>  create mode 100644 drivers/iio/industrialio-counter.c
>  create mode 100644 include/linux/iio/counter.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 6f7721d1634c..24fc2dcf1995 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6577,6 +6577,13 @@ F:       Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>  F:     Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
>  F:     drivers/iio/adc/envelope-detector.c
>
> +IIO GENERIC COUNTER INTERFACE
> +M:     William Breathitt Gray <[e-mail]>
> +L:     [e-mail]
> +S:     Maintained
> +F:     drivers/iio/industrialio-counter.c
> +F:     include/linux/iio/counter.h
> +
>  IIO MULTIPLEXER
>  M:     Peter Rosin <[e-mail]>
>  L:     [e-mail]
> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> index b3c8c6ef0dff..78e01f4f5937 100644
> --- a/drivers/iio/Kconfig
> +++ b/drivers/iio/Kconfig
> @@ -30,6 +30,14 @@ config IIO_CONFIGFS
>           (e.g. software triggers). For more info see
>           Documentation/iio/iio_configfs.txt.
>
> +config IIO_COUNTER
> +       bool "Enable IIO counter support"
> +       help
> +         Provides IIO core support for counters. This API provides
> +         a generic interface that serves as the building blocks to
> +         create more complex counter interfaces. Rudimentary support
> +         for counters is enabled.
> +
>  config IIO_TRIGGER
>         bool "Enable triggered sampling support"
>         help
> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> index 93c769cd99bf..6427ff38f964 100644
> --- a/drivers/iio/Makefile
> +++ b/drivers/iio/Makefile
> @@ -5,6 +5,7 @@
>  obj-$(CONFIG_IIO) += industrialio.o
>  industrialio-y := industrialio-core.o industrialio-event.o inkern.o
>  industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
> +industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
>  industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
>
>  obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
> diff --git a/drivers/iio/counter/Kconfig b/drivers/iio/counter/Kconfig
> index b37e5fc03149..3d46a790d8db 100644
> --- a/drivers/iio/counter/Kconfig
> +++ b/drivers/iio/counter/Kconfig
> @@ -4,6 +4,7 @@
>  # When adding new entries keep the list in alphabetical order
>
>  menu "Counters"
> +       depends on IIO_COUNTER
>
>  config 104_QUAD_8
>         tristate "ACCES 104-QUAD-8 driver"
> diff --git a/drivers/iio/industrialio-counter.c b/drivers/iio/industrialio-counter.c
> new file mode 100644
> index 000000000000..bdf190d010e4
> --- /dev/null
> +++ b/drivers/iio/industrialio-counter.c
> @@ -0,0 +1,1151 @@
> +/*
> + * Industrial I/O counter interface functions
> + * Copyright (C) 2017 William Breathitt Gray
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License, version 2, as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +#include <linux/err.h>
> +#include <linux/export.h>
> +#include <linux/gfp.h>
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/mutex.h>
> +#include <linux/printk.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/types.h>
> +
> +#include <linux/iio/counter.h>
> +
> +static struct iio_counter_signal *iio_counter_signal_find_by_id(
> +       const struct iio_counter *const counter, const int id)
> +{
> +       struct iio_counter_signal *iter;
> +
> +       list_for_each_entry(iter, &counter->signal_list, list)
> +               if (iter->id == id)
> +                       return iter;
> +
> +       return NULL;
> +}
> +
> +static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
> +       const struct iio_counter_value *const value, const int id)
> +{
> +       struct iio_counter_trigger *iter;
> +
> +       list_for_each_entry(iter, &value->trigger_list, list)
> +               if (iter->signal->id == id)
> +                       return iter;
> +
> +       return NULL;
> +}
> +
> +static struct iio_counter_value *iio_counter_value_find_by_id(
> +       const struct iio_counter *const counter, const int id)
> +{
> +       struct iio_counter_value *iter;
> +
> +       list_for_each_entry(iter, &counter->value_list, list)
> +               if (iter->id == id)
> +                       return iter;
> +
> +       return NULL;
> +}
> +
> +static void iio_counter_trigger_unregister_all(
> +       struct iio_counter_value *const value)
> +{
> +       struct iio_counter_trigger *iter, *tmp_iter;
> +
> +       mutex_lock(&value->trigger_list_lock);
> +       list_for_each_entry_safe(iter, tmp_iter, &value->trigger_list, list)
> +               list_del(&iter->list);
> +       mutex_unlock(&value->trigger_list_lock);
> +}
> +
> +static void iio_counter_signal_unregister_all(struct iio_counter *const counter)
> +{
> +       struct iio_counter_signal *iter, *tmp_iter;
> +
> +       mutex_lock(&counter->signal_list_lock);
> +       list_for_each_entry_safe(iter, tmp_iter, &counter->signal_list, list)
> +               list_del(&iter->list);
> +       mutex_unlock(&counter->signal_list_lock);
> +}
> +
> +static void iio_counter_value_unregister_all(struct iio_counter *const counter)
> +{
> +       struct iio_counter_value *iter, *tmp_iter;
> +
> +       mutex_lock(&counter->value_list_lock);
> +       list_for_each_entry_safe(iter, tmp_iter, &counter->value_list, list) {
> +               iio_counter_trigger_unregister_all(iter);
> +
> +               list_del(&iter->list);
> +       }
> +       mutex_unlock(&counter->value_list_lock);
> +}
> +
> +static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       const struct iio_counter_signal *signal;
> +
> +       mutex_lock(&counter->signal_list_lock);
> +       signal = iio_counter_signal_find_by_id(counter, chan->channel2);
> +       mutex_unlock(&counter->signal_list_lock);
> +       if (!signal)
> +               return -EINVAL;
> +
> +       return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
> +}
> +
> +static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,
> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       const struct iio_counter_value *value;
> +
> +       mutex_lock(&counter->value_list_lock);
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       mutex_unlock(&counter->value_list_lock);
> +       if (!value)
> +               return -EINVAL;
> +
> +       return scnprintf(buf, PAGE_SIZE, "%s\n", value->name);
> +}
> +
> +static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       const struct iio_counter_trigger *trigger;
> +       ssize_t len = 0;
> +
> +       mutex_lock(&counter->value_list_lock);
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               len = -EINVAL;
> +               goto err_find_value;
> +       }
> +
> +       mutex_lock(&value->trigger_list_lock);
> +       list_for_each_entry(trigger, &value->trigger_list, list) {
> +               len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
> +                       trigger->signal->id, trigger->signal->name,
> +                       trigger->trigger_modes[trigger->mode]);
> +               if (len >= PAGE_SIZE) {
> +                       len = -ENOMEM;
> +                       goto err_no_buffer_space;
> +               }
> +       }
> +err_no_buffer_space:
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +err_find_value:
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return len;
> +}
> +
> +static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       ssize_t ret;
> +       struct iio_counter_trigger *trigger;
> +       const int signal_id = *(int *)((void *)priv);
> +       int mode;
> +
> +       if (!counter->ops->trigger_mode_get)
> +               return -EINVAL;
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               ret = -EINVAL;
> +               goto err_value;
> +       }
> +
> +       mutex_lock(&value->trigger_list_lock);
> +
> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
> +       if (!trigger) {
> +               ret = -EINVAL;
> +               goto err_trigger;
> +       }
> +
> +       mode = counter->ops->trigger_mode_get(counter, value, trigger);
> +
> +       if (mode < 0) {
> +               ret = mode;
> +               goto err_trigger;
> +       } else if (mode >= trigger->num_trigger_modes) {
> +               ret = -EINVAL;
> +               goto err_trigger;
> +       }
> +
> +       trigger->mode = mode;
> +
> +       ret = scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
> +
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return ret;
> +
> +err_trigger:
> +       mutex_unlock(&value->trigger_list_lock);
> +err_value:
> +       mutex_unlock(&counter->value_list_lock);
> +       return ret;
> +}
> +
> +static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
> +       uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
> +       size_t len)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       ssize_t err;
> +       struct iio_counter_trigger *trigger;
> +       const int signal_id = *(int *)((void *)priv);
> +       unsigned int mode;
> +
> +       if (!counter->ops->trigger_mode_set)
> +               return -EINVAL;
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               err = -EINVAL;
> +               goto err_value;
> +       }
> +
> +       mutex_lock(&value->trigger_list_lock);
> +
> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
> +       if (!trigger) {
> +               err = -EINVAL;
> +               goto err_trigger;
> +       }
> +
> +       for (mode = 0; mode < trigger->num_trigger_modes; mode++)
> +               if (sysfs_streq(buf, trigger->trigger_modes[mode]))
> +                       break;
> +
> +       if (mode >= trigger->num_trigger_modes) {
> +               err = -EINVAL;
> +               goto err_trigger;
> +       }
> +
> +       err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
> +       if (err)
> +               goto err_trigger;
> +
> +       trigger->mode = mode;
> +
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return len;
> +
> +err_trigger:
> +       mutex_unlock(&value->trigger_list_lock);
> +err_value:
> +       mutex_unlock(&counter->value_list_lock);
> +       return err;
> +}
> +
> +static ssize_t iio_counter_trigger_mode_available_read(
> +       struct iio_dev *indio_dev, uintptr_t priv,
> +       const struct iio_chan_spec *chan, char *buf)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       ssize_t len = 0;
> +       struct iio_counter_trigger *trigger;
> +       const int signal_id = *(int *)((void *)priv);
> +       unsigned int i;
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               len = -EINVAL;
> +               goto err_no_value;
> +       }
> +
> +       mutex_lock(&value->trigger_list_lock);
> +
> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
> +       if (!trigger) {
> +               len = -EINVAL;
> +               goto err_no_trigger;
> +       }
> +
> +       for (i = 0; i < trigger->num_trigger_modes; i++)
> +               len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
> +                       trigger->trigger_modes[i]);
> +
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       buf[len - 1] = '\n';
> +
> +       return len;
> +
> +err_no_trigger:
> +       mutex_unlock(&value->trigger_list_lock);
> +err_no_value:
> +       mutex_unlock(&counter->value_list_lock);
> +       return len;
> +}
> +
> +static int iio_counter_value_function_set(struct iio_dev *indio_dev,
> +       const struct iio_chan_spec *chan, unsigned int mode)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       int err;
> +
> +       if (!counter->ops->value_function_set)
> +               return -EINVAL;
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               err = -EINVAL;
> +               goto err_value;
> +       }
> +
> +       err = counter->ops->value_function_set(counter, value, mode);
> +       if (err)
> +               goto err_value;
> +
> +       value->mode = mode;
> +
> +err_value:
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return err;
> +}
> +
> +static int iio_counter_value_function_get(struct iio_dev *indio_dev,
> +       const struct iio_chan_spec *chan)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_value *value;
> +       int retval;
> +
> +       if (!counter->ops->value_function_get)
> +               return -EINVAL;
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
> +       if (!value) {
> +               retval = -EINVAL;
> +               goto err_value;
> +       }
> +
> +       retval = counter->ops->value_function_get(counter, value);
> +       if (retval < 0)
> +               goto err_value;
> +       else if (retval >= value->num_function_modes) {
> +               retval = -EINVAL;
> +               goto err_value;
> +       }
> +
> +       value->mode = retval;
> +
> +err_value:
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return retval;
> +}
> +
> +static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
> +       struct iio_counter_value *const value)
> +{
> +       const struct iio_chan_spec_ext_info ext_info_default[] = {
> +               {
> +                       .name = "name",
> +                       .shared = IIO_SEPARATE,
> +                       .read = iio_counter_value_name_read
> +               },
> +               IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
> +               {
> +                       .name = "function_available",
> +                       .shared = IIO_SEPARATE,
> +                       .read = iio_enum_available_read,
> +                       .private = (void *)&value->function_enum
I have this warning the 3 times that  private field is set
drivers/iio/industrialio-counter.c:401:15: warning: initialization
makes integer from pointer without a cast [-Wint-conversion]
    .private = (void *)&value->function_enum

I think you can change it to "void *" instead of a uintptr_t
> +               },
> +               {
> +                       .name = "triggers",
> +                       .shared = IIO_SEPARATE,
> +                       .read = iio_counter_value_triggers_read
> +               }
> +       };
> +       const size_t num_default = ARRAY_SIZE(ext_info_default);
> +       const struct iio_chan_spec_ext_info ext_info_trigger[] = {
> +               {
> +                       .shared = IIO_SEPARATE,
> +                       .read = iio_counter_trigger_mode_read,
> +                       .write = iio_counter_trigger_mode_write
> +               },
> +               {
> +                       .shared = IIO_SEPARATE,
> +                       .read = iio_counter_trigger_mode_available_read
> +               }
> +       };
> +       const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
> +       const struct list_head *pos;
> +       size_t num_triggers = 0;
> +       size_t num_triggers_ext_info;
> +       size_t num_ext_info;
> +       int err;
> +       struct iio_chan_spec_ext_info *ext_info;
> +       const struct iio_counter_trigger *trigger_pos;
> +       size_t i;
> +
> +       value->function_enum.items = value->function_modes;
> +       value->function_enum.num_items = value->num_function_modes;
> +       value->function_enum.set = iio_counter_value_function_set;
> +       value->function_enum.get = iio_counter_value_function_get;
> +
> +       mutex_lock(&value->trigger_list_lock);
> +
> +       list_for_each(pos, &value->trigger_list)
> +               num_triggers++;
> +
> +       num_triggers_ext_info = num_ext_info_trigger * num_triggers;
> +       num_ext_info = num_default + num_triggers_ext_info + 1;
> +
> +       ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
> +       if (!ext_info) {
> +               err = -ENOMEM;
> +               goto err_ext_info_alloc;
> +       }
> +       ext_info[num_ext_info - 1].name = NULL;
> +
> +       memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
> +       for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
> +               memcpy(ext_info + num_default + i, ext_info_trigger,
> +                       sizeof(ext_info_trigger));
> +
> +       i = num_default;
> +       list_for_each_entry(trigger_pos, &value->trigger_list, list) {
> +               ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
> +                       chan->channel, trigger_pos->signal->id);
> +               if (!ext_info[i].name) {
> +                       err = -ENOMEM;
> +                       goto err_name_alloc;
> +               }
> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
> +               i++;
> +
> +               ext_info[i].name = kasprintf(GFP_KERNEL,
> +                       "trigger_signal%d-%d_available",
> +                       chan->channel, trigger_pos->signal->id);
> +               if (!ext_info[i].name) {
> +                       err = -ENOMEM;
> +                       goto err_name_alloc;
> +               }
> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
> +               i++;
> +       }
> +
> +       chan->ext_info = ext_info;
> +
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +       return 0;
> +
> +err_name_alloc:
> +       while (i-- > num_default)
> +               kfree(ext_info[i].name);
> +       kfree(ext_info);
> +err_ext_info_alloc:
> +       mutex_unlock(&value->trigger_list_lock);
> +       return err;
> +}
> +
> +static void iio_counter_value_ext_info_free(
> +       const struct iio_chan_spec *const channel)
> +{
> +       size_t i;
> +       const char *const prefix = "trigger_signal";
> +       const size_t prefix_len = strlen(prefix);
> +
> +       for (i = 0; channel->ext_info[i].name; i++)
> +               if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
> +                       kfree(channel->ext_info[i].name);
> +       kfree(channel->ext_info);
> +}
> +
> +static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
> +       {
> +               .name = "name",
> +               .shared = IIO_SEPARATE,
> +               .read = iio_counter_signal_name_read
> +       },
> +       {}
> +};
> +
> +static int iio_counter_channels_alloc(struct iio_counter *const counter)
> +{
> +       const struct list_head *pos;
> +       size_t num_channels = 0;
> +       int err;
> +       struct iio_chan_spec *channels;
> +       struct iio_counter_value *value_pos;
> +       size_t i = counter->num_channels;
> +       const struct iio_counter_signal *signal_pos;
> +
> +       mutex_lock(&counter->signal_list_lock);
> +
> +       list_for_each(pos, &counter->signal_list)
> +               num_channels++;
> +
> +       if (!num_channels) {
> +               err = -EINVAL;
> +               goto err_no_signals;
> +       }
> +
> +       mutex_lock(&counter->value_list_lock);
> +
> +       list_for_each(pos, &counter->value_list)
> +               num_channels++;
> +
> +       num_channels += counter->num_channels;
> +
> +       channels = kcalloc(num_channels, sizeof(*channels), GFP_KERNEL);
> +       if (!channels) {
> +               err = -ENOMEM;
> +               goto err_channels_alloc;
> +       }
> +
> +       memcpy(channels, counter->channels,
> +               counter->num_channels * sizeof(*counter->channels));
> +
> +       list_for_each_entry(value_pos, &counter->value_list, list) {
> +               channels[i].type = IIO_COUNT;
> +               channels[i].channel = counter->id;
> +               channels[i].channel2 = value_pos->id;
> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
> +               channels[i].indexed = 1;
> +               channels[i].counter = 1;
> +
> +               err = iio_counter_value_ext_info_alloc(channels + i, value_pos);
> +               if (err)
> +                       goto err_value_ext_info_alloc;
> +
> +               i++;
> +       }
> +
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       list_for_each_entry(signal_pos, &counter->signal_list, list) {
> +               channels[i].type = IIO_SIGNAL;
> +               channels[i].channel = counter->id;
> +               channels[i].channel2 = signal_pos->id;
> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
> +               channels[i].indexed = 1;
> +               channels[i].counter = 1;
> +               channels[i].ext_info = iio_counter_signal_ext_info;
> +
> +               i++;
> +       }
> +
> +       mutex_unlock(&counter->signal_list_lock);
> +
> +       counter->indio_dev->num_channels = num_channels;
> +       counter->indio_dev->channels = channels;
> +
> +       return 0;
> +
> +err_value_ext_info_alloc:
> +       while (i-- > counter->num_channels)
> +               iio_counter_value_ext_info_free(channels + i);
> +       kfree(channels);
> +err_channels_alloc:
> +       mutex_unlock(&counter->value_list_lock);
> +err_no_signals:
> +       mutex_unlock(&counter->signal_list_lock);
> +       return err;
> +}
> +
> +static void iio_counter_channels_free(const struct iio_counter *const counter)
> +{
> +       size_t i = counter->num_channels + counter->indio_dev->num_channels;
> +       const struct iio_chan_spec *const chans = counter->indio_dev->channels;
> +
> +       while (i-- > counter->num_channels)
> +               if (chans[i].type == IIO_COUNT)
> +                       iio_counter_value_ext_info_free(chans + i);
> +
> +       kfree(chans);
> +}
> +
> +static int iio_counter_read_raw(struct iio_dev *indio_dev,
> +       struct iio_chan_spec const *chan, int *val, int *val2, long mask)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_signal *signal;
> +       int retval;
> +       struct iio_counter_value *value;
> +
> +       if (mask != IIO_CHAN_INFO_RAW)
> +               return -EINVAL;
> +
> +       switch (chan->type) {
> +       case IIO_SIGNAL:
> +               if (!counter->ops->signal_read)
> +                       return -EINVAL;
> +
> +               mutex_lock(&counter->signal_list_lock);
> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
> +               if (!signal) {
> +                       mutex_unlock(&counter->signal_list_lock);
> +                       return -EINVAL;
> +               }
> +
> +               retval = counter->ops->signal_read(counter, signal, val, val2);
> +               mutex_unlock(&counter->signal_list_lock);
> +
> +               return retval;
> +       case IIO_COUNT:
> +               if (!counter->ops->value_read)
> +                       return -EINVAL;
> +
> +               mutex_lock(&counter->value_list_lock);
> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
> +               if (!value) {
> +                       mutex_unlock(&counter->value_list_lock);
> +                       return -EINVAL;
> +               }
> +
> +               retval = counter->ops->value_read(counter, value, val, val2);
> +               mutex_unlock(&counter->value_list_lock);
> +
> +               return retval;
> +       default:
> +               if (counter->info && counter->info->read_raw)
> +                       return counter->info->read_raw(indio_dev, chan, val,
> +                               val2, mask);
> +       }
> +
> +       return -EINVAL;
> +}
> +
> +static int iio_counter_write_raw(struct iio_dev *indio_dev,
> +       struct iio_chan_spec const *chan, int val, int val2, long mask)
> +{
> +       struct iio_counter *const counter = iio_priv(indio_dev);
> +       struct iio_counter_signal *signal;
> +       int retval;
> +       struct iio_counter_value *value;
> +
> +       if (mask != IIO_CHAN_INFO_RAW)
> +               return -EINVAL;
> +
> +       switch (chan->type) {
> +       case IIO_SIGNAL:
> +               if (!counter->ops->signal_write)
> +                       return -EINVAL;
> +
> +               mutex_lock(&counter->signal_list_lock);
> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
> +               if (!signal) {
> +                       mutex_unlock(&counter->signal_list_lock);
> +                       return -EINVAL;
> +               }
> +
> +               retval = counter->ops->signal_write(counter, signal, val, val2);
> +               mutex_unlock(&counter->signal_list_lock);
> +
> +               return retval;
> +       case IIO_COUNT:
> +               if (!counter->ops->value_write)
> +                       return -EINVAL;
> +
> +               mutex_lock(&counter->value_list_lock);
> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
> +               if (!value) {
> +                       mutex_unlock(&counter->value_list_lock);
> +                       return -EINVAL;
> +               }
> +
> +               retval = counter->ops->value_write(counter, value, val, val2);
> +               mutex_unlock(&counter->value_list_lock);
> +
> +               return retval;
> +       default:
> +               if (counter->info && counter->info->write_raw)
> +                       return counter->info->write_raw(indio_dev, chan, val,
> +                               val2, mask);
> +       }
> +
> +       return -EINVAL;
> +}
> +
> +static int iio_counter_signal_register(struct iio_counter *const counter,
> +       struct iio_counter_signal *const signal)
> +{
> +       int err;
> +
> +       if (!counter || !signal)
> +               return -EINVAL;
> +
> +       mutex_lock(&counter->signal_list_lock);
> +       if (iio_counter_signal_find_by_id(counter, signal->id)) {
> +               pr_err("Duplicate counter signal ID '%d'\n", signal->id);
> +               err = -EEXIST;
> +               goto err_duplicate_id;
> +       }
> +       list_add_tail(&signal->list, &counter->signal_list);
> +       mutex_unlock(&counter->signal_list_lock);
> +
> +       return 0;
> +
> +err_duplicate_id:
> +       mutex_unlock(&counter->signal_list_lock);
> +       return err;
> +}
> +
> +static void iio_counter_signal_unregister(struct iio_counter *const counter,
> +       struct iio_counter_signal *const signal)
> +{
> +       if (!counter || !signal)
> +               return;
> +
> +       mutex_lock(&counter->signal_list_lock);
> +       list_del(&signal->list);
> +       mutex_unlock(&counter->signal_list_lock);
> +}
> +
> +static int iio_counter_signals_register(struct iio_counter *const counter,
> +       struct iio_counter_signal *const signals, const size_t num_signals)
> +{
> +       size_t i;
> +       int err;
> +
> +       if (!counter || !signals)
> +               return -EINVAL;
> +
> +       for (i = 0; i < num_signals; i++) {
> +               err = iio_counter_signal_register(counter, signals + i);
> +               if (err)
> +                       goto err_signal_register;
> +       }
> +
> +       return 0;
> +
> +err_signal_register:
> +       while (i--)
> +               iio_counter_signal_unregister(counter, signals + i);
> +       return err;
> +}
> +
> +static void iio_counter_signals_unregister(struct iio_counter *const counter,
> +       struct iio_counter_signal *signals, size_t num_signals)
> +{
> +       if (!counter || !signals)
> +               return;
> +
> +       while (num_signals--) {
> +               iio_counter_signal_unregister(counter, signals);
> +               signals++;
> +       }
> +}
> +
> +/**
> + * iio_counter_trigger_register - register Trigger to Value
> + * @value: pointer to IIO Counter Value for association
> + * @trigger: pointer to IIO Counter Trigger to register
> + *
> + * The Trigger is added to the Value's trigger_list. A check is first performed
> + * to verify that the respective Signal is not already linked to the Value; if
> + * the respective Signal is already linked to the Value, the Trigger is not
> + * added to the Value's trigger_list.
> + *
> + * NOTE: This function will acquire and release the Value's trigger_list_lock
> + * during execution.
> + */
> +int iio_counter_trigger_register(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const trigger)
> +{
> +       if (!value || !trigger || !trigger->signal)
> +               return -EINVAL;
> +
> +       mutex_lock(&value->trigger_list_lock);
> +       if (iio_counter_trigger_find_by_id(value, trigger->signal->id)) {
> +               pr_err("Signal%d is already linked to counter value%d\n",
> +                       trigger->signal->id, value->id);
> +               return -EEXIST;
> +       }
> +       list_add_tail(&trigger->list, &value->trigger_list);
> +       mutex_unlock(&value->trigger_list_lock);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(iio_counter_trigger_register);
> +
> +/**
> + * iio_counter_trigger_unregister - unregister Trigger from Value
> + * @value: pointer to IIO Counter Value of association
> + * @trigger: pointer to IIO Counter Trigger to unregister
> + *
> + * The Trigger is removed from the Value's trigger_list.
> + *
> + * NOTE: This function will acquire and release the Value's trigger_list_lock
> + * during execution.
> + */
> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const trigger)
> +{
> +       if (!value || !trigger || !trigger->signal)
> +               return;
> +
> +       mutex_lock(&value->trigger_list_lock);
> +       list_del(&trigger->list);
> +       mutex_unlock(&value->trigger_list_lock);
> +}
> +EXPORT_SYMBOL(iio_counter_trigger_unregister);
> +
> +/**
> + * iio_counter_triggers_register - register an array of Triggers to Value
> + * @value: pointer to IIO Counter Value for association
> + * @triggers: array of pointers to IIO Counter Triggers to register
> + *
> + * The iio_counter_trigger_register function is called for each Trigger in the
> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
> + *
> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
> + */
> +int iio_counter_triggers_register(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const triggers, const size_t num_triggers)
> +{
> +       size_t i;
> +       int err;
> +
> +       if (!value || !triggers)
> +               return -EINVAL;
> +
> +       for (i = 0; i < num_triggers; i++) {
> +               err = iio_counter_trigger_register(value, triggers + i);
> +               if (err)
> +                       goto err_trigger_register;
> +       }
> +
> +       return 0;
> +
> +err_trigger_register:
> +       while (i--)
> +               iio_counter_trigger_unregister(value, triggers + i);
> +       return err;
> +}
> +EXPORT_SYMBOL(iio_counter_triggers_register);
> +
> +/**
> + * iio_counter_triggers_unregister - unregister Triggers from Value
> + * @value: pointer to IIO Counter Value of association
> + * @triggers: array of pointers to IIO Counter Triggers to unregister
> + *
> + * The iio_counter_trigger_unregister function is called for each Trigger in the
> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
> + *
> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
> + */
> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *triggers, size_t num_triggers)
> +{
> +       if (!value || !triggers)
> +               return;
> +
> +       while (num_triggers--) {
> +               iio_counter_trigger_unregister(value, triggers);
> +               triggers++;
> +       }
> +}
> +EXPORT_SYMBOL(iio_counter_triggers_unregister);
> +
> +/**
> + * iio_counter_value_register - register Value to Counter
> + * @counter: pointer to IIO Counter for association
> + * @value: pointer to IIO Counter Value to register
> + *
> + * The registration process occurs in two major steps. First, the Value is
> + * initialized: trigger_list_lock is initialized, trigger_list is initialized,
> + * and init_triggers if not NULL is passed to iio_counter_triggers_register.
> + * Second, the Value is added to the Counter's value_list. A check is first
> + * performed to verify that the Value is not already associated to the Counter
> + * (via the Value's unique ID); if the Value is already associated to the
> + * Counter, the Value is not added to the Counter's value_list and all of the
> + * Value's Triggers are unregistered.
> + *
> + * NOTE: This function will acquire and release the Counter's value_list_lock
> + * during execution.
> + */
> +int iio_counter_value_register(struct iio_counter *const counter,
> +       struct iio_counter_value *const value)
> +{
> +       int err;
> +
> +       if (!counter || !value)
> +               return -EINVAL;
> +
> +       mutex_init(&value->trigger_list_lock);
> +       INIT_LIST_HEAD(&value->trigger_list);
> +
> +       if (value->init_triggers) {
> +               err = iio_counter_triggers_register(value,
> +                       value->init_triggers, value->num_init_triggers);
> +               if (err)
> +                       return err;
> +       }
> +
> +       mutex_lock(&counter->value_list_lock);
> +       if (iio_counter_value_find_by_id(counter, value->id)) {
> +               pr_err("Duplicate counter value ID '%d'\n", value->id);
> +               err = -EEXIST;
> +               goto err_duplicate_id;
> +       }
> +       list_add_tail(&value->list, &counter->value_list);
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       return 0;
> +
> +err_duplicate_id:
> +       mutex_unlock(&counter->value_list_lock);
> +       iio_counter_trigger_unregister_all(value);
> +       return err;
> +}
> +EXPORT_SYMBOL(iio_counter_value_register);
> +
> +/**
> + * iio_counter_value_unregister - unregister Value from Counter
> + * @counter: pointer to IIO Counter of association
> + * @value: pointer to IIO Counter Value to unregister
> + *
> + * The Value is removed from the Counter's value_list and all of the Value's
> + * Triggers are unregistered.
> + *
> + * NOTE: This function will acquire and release the Counter's value_list_lock
> + * during execution.
> + */
> +void iio_counter_value_unregister(struct iio_counter *const counter,
> +       struct iio_counter_value *const value)
> +{
> +       if (!counter || !value)
> +               return;
> +
> +       mutex_lock(&counter->value_list_lock);
> +       list_del(&value->list);
> +       mutex_unlock(&counter->value_list_lock);
> +
> +       iio_counter_trigger_unregister_all(value);
> +}
> +EXPORT_SYMBOL(iio_counter_value_unregister);
> +
> +/**
> + * iio_counter_values_register - register an array of Values to Counter
> + * @counter: pointer to IIO Counter for association
> + * @values: array of pointers to IIO Counter Values to register
> + *
> + * The iio_counter_value_register function is called for each Value in the
> + * array. The @values array is traversed for the first @num_values Values.
> + *
> + * NOTE: @num_values must not be greater than the size of the @values array.
> + */
> +int iio_counter_values_register(struct iio_counter *const counter,
> +       struct iio_counter_value *const values, const size_t num_values)
> +{
> +       size_t i;
> +       int err;
> +
> +       if (!counter || !values)
> +               return -EINVAL;
> +
> +       for (i = 0; i < num_values; i++) {
> +               err = iio_counter_value_register(counter, values + i);
> +               if (err)
> +                       goto err_values_register;
> +       }
> +
> +       return 0;
> +
> +err_values_register:
> +       while (i--)
> +               iio_counter_value_unregister(counter, values + i);
> +       return err;
> +}
> +EXPORT_SYMBOL(iio_counter_values_register);
> +
> +/**
> + * iio_counter_values_unregister - unregister Values from Counter
> + * @counter: pointer to IIO Counter of association
> + * @values: array of pointers to IIO Counter Values to unregister
> + *
> + * The iio_counter_value_unregister function is called for each Value in the
> + * array. The @values array is traversed for the first @num_values Values.
> + *
> + * NOTE: @num_values must not be greater than the size of the @values array.
> + */
> +void iio_counter_values_unregister(struct iio_counter *const counter,
> +       struct iio_counter_value *values, size_t num_values)
> +{
> +       if (!counter || !values)
> +               return;
> +
> +       while (num_values--) {
> +               iio_counter_value_unregister(counter, values);
> +               values++;
> +       }
> +}
> +EXPORT_SYMBOL(iio_counter_values_unregister);
> +
> +/**
> + * iio_counter_register - register Counter to the system
> + * @counter: pointer to IIO Counter to register
> + *
> + * This function piggybacks off of iio_device_register. First, the relevant
> + * Counter members are initialized; if init_signals is not NULL it is passed to
> + * iio_counter_signals_register, and similarly if init_values is not NULL it is
> + * passed to iio_counter_values_register. Next, a struct iio_dev is allocated by
> + * a call to iio_device_alloc and initialized for the Counter, IIO channels are
> + * allocated, the Counter is copied as the private data, and finally
> + * iio_device_register is called.
> + */
> +int iio_counter_register(struct iio_counter *const counter)
> +{
> +       const struct iio_info info_default = {
> +               .read_raw = iio_counter_read_raw,
> +               .write_raw = iio_counter_write_raw
> +       };
> +       int err;
> +       struct iio_info *info;
> +       struct iio_counter *priv;
> +
> +       if (!counter)
> +               return -EINVAL;
> +
> +       mutex_init(&counter->signal_list_lock);
> +       INIT_LIST_HEAD(&counter->signal_list);
> +
> +       if (counter->init_signals) {
> +               err = iio_counter_signals_register(counter,
> +                       counter->init_signals, counter->num_init_signals);
> +               if (err)
> +                       return err;
> +       }
> +
> +       mutex_init(&counter->value_list_lock);
> +       INIT_LIST_HEAD(&counter->value_list);
> +
> +       if (counter->init_values) {
> +               err = iio_counter_values_register(counter,
> +                       counter->init_values, counter->num_init_values);
> +               if (err)
> +                       goto err_values_register;
> +       }
> +
> +       counter->indio_dev = iio_device_alloc(sizeof(*counter));
> +       if (!counter->indio_dev) {
> +               err = -ENOMEM;
> +               goto err_iio_device_alloc;
> +       }
> +
> +       info = kmalloc(sizeof(*info), GFP_KERNEL);
> +       if (!info) {
> +               err = -ENOMEM;
> +               goto err_info_alloc;
> +       }
> +       if (counter->info) {
> +               memcpy(info, counter->info, sizeof(*counter->info));
> +               info->read_raw = iio_counter_read_raw;
> +               info->write_raw = iio_counter_write_raw;
> +       } else {
> +               memcpy(info, &info_default, sizeof(info_default));
> +       }
> +
> +       counter->indio_dev->info = info;
> +       counter->indio_dev->modes = INDIO_DIRECT_MODE;
> +       counter->indio_dev->name = counter->name;
> +       counter->indio_dev->dev.parent = counter->dev;
> +
> +       err = iio_counter_channels_alloc(counter);
> +       if (err)
> +               goto err_channels_alloc;
> +
> +       priv = iio_priv(counter->indio_dev);
> +       memcpy(priv, counter, sizeof(*priv));
> +
> +       err = iio_device_register(priv->indio_dev);
> +       if (err)
> +               goto err_iio_device_register;
> +
> +       return 0;
> +
> +err_iio_device_register:
> +       iio_counter_channels_free(counter);
> +err_channels_alloc:
> +       kfree(info);
> +err_info_alloc:
> +       iio_device_free(counter->indio_dev);
> +err_iio_device_alloc:
> +       iio_counter_values_unregister(counter, counter->init_values,
> +               counter->num_init_values);
> +err_values_register:
> +       iio_counter_signals_unregister(counter, counter->init_signals,
> +               counter->num_init_signals);
> +       return err;
> +}
> +EXPORT_SYMBOL(iio_counter_register);
> +
> +/**
> + * iio_counter_unregister - unregister Counter from the system
> + * @counter: pointer to IIO Counter to unregister
> + *
> + * The Counter is unregistered from the system. The indio_dev is unregistered,
> + * allocated memory is freed, and all associated Values and Signals are
> + * unregistered.
> + */
> +void iio_counter_unregister(struct iio_counter *const counter)
> +{
> +       const struct iio_info *const info = counter->indio_dev->info;
> +
> +       if (!counter)
> +               return;
> +
> +       iio_device_unregister(counter->indio_dev);
> +
> +       iio_counter_channels_free(counter);
> +
> +       kfree(info);
> +       iio_device_free(counter->indio_dev);
> +
> +       iio_counter_value_unregister_all(counter);
> +       iio_counter_signal_unregister_all(counter);
> +}
> +EXPORT_SYMBOL(iio_counter_unregister);
> diff --git a/include/linux/iio/counter.h b/include/linux/iio/counter.h
> new file mode 100644
> index 000000000000..1c1ca13a6053
> --- /dev/null
> +++ b/include/linux/iio/counter.h
> @@ -0,0 +1,221 @@
> +/*
> + * Industrial I/O counter interface
> + * Copyright (C) 2017 William Breathitt Gray
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License, version 2, as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +#ifndef _IIO_COUNTER_H_
> +#define _IIO_COUNTER_H_
> +
> +#ifdef CONFIG_IIO_COUNTER
> +
> +#include <linux/device.h>
> +#include <linux/mutex.h>
> +#include <linux/types.h>
> +
> +#include <linux/iio/iio.h>
> +
> +/**
> + * struct iio_counter_signal - IIO Counter Signal node
> + * @id:                [DRIVER] unique ID used to identify signal
> + * @name:      [DRIVER] device-specific signal name
> + * @list:      [INTERN] list of all signals currently registered to counter
> + */
> +struct iio_counter_signal {
> +       int             id;
> +       const char      *name;
> +
> +       struct list_head        list;
> +};
> +
> +/**
> + * struct iio_counter_trigger - IIO Counter Trigger node
> + * @mode:              [DRIVER] current trigger mode state
> + * @trigger_modes:     [DRIVER] available trigger modes
> + * @num_trigger_modes: [DRIVER] number of modes specified in @trigger_modes
> + * @signal:            [DRIVER] pointer to associated signal
> + * @list:              [INTERN] list of all triggers currently registered to
> + *                     value
> + */
> +struct iio_counter_trigger {
> +       unsigned int                    mode;
> +       const char *const               *trigger_modes;
> +       unsigned int                    num_trigger_modes;
> +       struct iio_counter_signal       *signal;
> +
> +       struct list_head                list;
> +};
> +
> +/**
> + * struct iio_counter_value - IIO Counter Value node
> + * @id:                        [DRIVER] unique ID used to identify value
> + * @name:              [DRIVER] device-specific value name
> + * @mode:              [DRIVER] current function mode state
> + * @function_modes:    [DRIVER] available function modes
> + * @num_function_modes:        [DRIVER] number of modes specified in @function_modes
> + * @init_triggers:     [DRIVER] array of triggers for initialization
> + * @num_init_triggers: [DRIVER] number of triggers specified in @init_triggers
> + * @function_enum:     [INTERN] used internally to generate function attributes
> + * @trigger_list_lock: [INTERN] lock for accessing @trigger_list
> + * @trigger_list:      [INTERN] list of all triggers currently registered to
> + *                     value
> + * @list:              [INTERN] list of all values currently registered to
> + *                     counter
> + */
> +struct iio_counter_value {
> +       int                     id;
> +       const char              *name;
> +       unsigned int            mode;
> +       const char *const       *function_modes;
> +       unsigned int            num_function_modes;
> +
> +       struct iio_counter_trigger      *init_triggers;
> +       size_t                          num_init_triggers;
> +
> +       struct iio_enum         function_enum;
> +       struct mutex            trigger_list_lock;
> +       struct list_head        trigger_list;
> +
> +       struct list_head        list;
> +};
> +
> +struct iio_counter;
> +
> +/**
> + * struct iio_counter_ops - IIO Counter related callbacks
> + * @signal_read:       function to request a signal value from the device.
> + *                     Return value will specify the type of value returned by
> + *                     the device. val and val2 will contain the elements
> + *                     making up the returned value. Note that the counter
> + *                     signal_list_lock is acquired before this function is
> + *                     called, and released after this function returns.
> + * @signal_write:      function to write a signal value to the device.
> + *                     Parameters and locking behavior are the same as
> + *                     signal_read.
> + * @trigger_mode_set:  function to set the trigger mode. mode is the index of
> + *                     the requested mode from the value trigger_modes array.
> + *                     Note that the counter value_list_lock and value
> + *                     trigger_list_lock are acquired before this function is
> + *                     called, and released after this function returns.
> + * @trigger_mode_get:  function to get the current trigger mode. Return value
> + *                     will specify the index of the current mode from the
> + *                     value trigger_modes array. Locking behavior is the same
> + *                     as trigger_mode_set.
> + * @value_read:                function to request a value value from the device.
> + *                     Return value will specify the type of value returned by
> + *                     the device. val and val2 will contain the elements
> + *                     making up the returned value. Note that the counter
> + *                     value_list_lock is acquired before this function is
> + *                     called, and released after this function returns.
> + * @value_write:       function to write a value value to the device.
> + *                     Parameters and locking behavior are the same as
> + *                     value_read.
> + * @value_function_set: function to set the value function mode. mode is the
> + *                     index of the requested mode from the value
> + *                     function_modes array. Note that the counter
> + *                     value_list_lock is acquired before this function is
> + *                     called, and released after this function returns.
> + * @value_function_get: function to get the current value function mode. Return
> + *                     value will specify the index of the current mode from
> + *                     the value function_modes array. Locking behavior is the
> + *                     same as value_function_get.
> + */
> +struct iio_counter_ops {
> +       int (*signal_read)(struct iio_counter *counter,
> +               struct iio_counter_signal *signal, int *val, int *val2);
> +       int (*signal_write)(struct iio_counter *counter,
> +               struct iio_counter_signal *signal, int val, int val2);
> +       int (*trigger_mode_set)(struct iio_counter *counter,
> +               struct iio_counter_value *value,
> +               struct iio_counter_trigger *trigger, unsigned int mode);
> +       int (*trigger_mode_get)(struct iio_counter *counter,
> +               struct iio_counter_value *value,
> +               struct iio_counter_trigger *trigger);
> +       int (*value_read)(struct iio_counter *counter,
> +               struct iio_counter_value *value, int *val, int *val2);
> +       int (*value_write)(struct iio_counter *counter,
> +               struct iio_counter_value *value, int val, int val2);
> +       int (*value_function_set)(struct iio_counter *counter,
> +               struct iio_counter_value *value, unsigned int mode);
> +       int (*value_function_get)(struct iio_counter *counter,
> +               struct iio_counter_value *value);
> +};
> +
> +/**
> + * struct iio_counter - IIO Counter data structure
> + * @id:                        [DRIVER] unique ID used to identify counter
> + * @name:              [DRIVER] name of the device
> + * @dev:               [DRIVER] device structure, should be assigned a parent
> + *                     and owner
> + * @ops:               [DRIVER] callbacks from driver for counter components
> + * @init_signals:      [DRIVER] array of signals for initialization
> + * @num_init_signals:  [DRIVER] number of signals specified in @init_signals
> + * @init_values:       [DRIVER] array of values for initialization
> + * @num_init_values:   [DRIVER] number of values specified in @init_values
> + * @signal_list_lock:  [INTERN] lock for accessing @signal_list
> + * @signal_list:       [INTERN] list of all signals currently registered to
> + *                     counter
> + * @value_list_lock:   [INTERN] lock for accessing @value_list
> + * @value_list:                [INTERN] list of all values currently registered to
> + *                     counter
> + * @channels:          [DRIVER] channel specification structure table
> + * @num_channels:      [DRIVER] number of channels specified in @channels
> + * @info:              [DRIVER] callbacks and constant info from driver
> + * @indio_dev:         [INTERN] industrial I/O device structure
> + * @driver_data:       [DRIVER] driver data
> + */
> +struct iio_counter {
> +       int                             id;
> +       const char                      *name;
> +       struct device                   *dev;
> +       const struct iio_counter_ops    *ops;
> +
> +       struct iio_counter_signal       *init_signals;
> +       size_t                          num_init_signals;
> +       struct iio_counter_value        *init_values;
> +       size_t                          num_init_values;
> +
> +       struct mutex            signal_list_lock;
> +       struct list_head        signal_list;
> +       struct mutex            value_list_lock;
> +       struct list_head        value_list;
> +
> +       const struct iio_chan_spec      *channels;
> +       size_t                          num_channels;
> +       const struct iio_info           *info;
> +
> +       struct iio_dev  *indio_dev;
> +       void            *driver_data;
> +};
> +
> +int iio_counter_trigger_register(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const trigger);
> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const trigger);
> +int iio_counter_triggers_register(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *const triggers, const size_t num_triggers);
> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
> +       struct iio_counter_trigger *triggers, size_t num_triggers);
> +
> +int iio_counter_value_register(struct iio_counter *const counter,
> +       struct iio_counter_value *const value);
> +void iio_counter_value_unregister(struct iio_counter *const counter,
> +       struct iio_counter_value *const value);
> +int iio_counter_values_register(struct iio_counter *const counter,
> +       struct iio_counter_value *const values, const size_t num_values);
> +void iio_counter_values_unregister(struct iio_counter *const counter,
> +       struct iio_counter_value *values, size_t num_values);
> +
> +int iio_counter_register(struct iio_counter *const counter);
> +void iio_counter_unregister(struct iio_counter *const counter);
> +
> +#endif /* CONFIG_IIO_COUNTER */
> +
> +#endif /* _IIO_COUNTER_H_ */
> --
> 2.14.1
>

William Breathitt Gray Sept. 29, 2017, 8:01 p.m. UTC | #2

On Fri, Sep 29, 2017 at 03:42:02PM +0200, Benjamin Gaignard wrote:
>2017-09-25 20:08 GMT+02:00 William Breathitt Gray <[e-mail]>:
>> This patch introduces the IIO generic counter interface for supporting
>> counter devices. The generic counter interface serves as a catch-all to
>> enable rudimentary support for devices that qualify as counters. More
>> specific and apt counter interfaces may be developed on top of the
>> generic counter interface, and those interfaces should be used by
>> drivers when possible rather than the generic counter interface.
>>
>> In the context of the IIO generic counter interface, a counter is
>> defined as a device that reports one or more "counter values" based on
>> the state changes of one or more "counter signals" as evaluated by a
>> defined "counter function."
>>
>> The IIO generic counter interface piggybacks off of the IIO core. This
>> is primarily used to leverage the existing sysfs setup: the IIO_COUNT
>> channel attributes represent the "counter value," while the IIO_SIGNAL
>> channel attributes represent the "counter signal;" auxilary IIO_COUNT
>> attributes represent the "counter signal" connections and their
>> respective state change configurations which trigger an associated
>> "counter function" evaluation.
>>
>> The iio_counter_ops structure serves as a container for driver callbacks
>> to communicate with the device; function callbacks are provided to read
>> and write various "counter signals" and "counter values," and set and
>> get the "trigger mode" and "function mode" for various "counter signals"
>> and "counter values" respectively.
>>
>> To support a counter device, a driver must first allocate the available
>> "counter signals" via iio_counter_signal structures. These "counter
>> signals" should be stored as an array and set to the init_signals member
>> of an allocated iio_counter structure before the counter is registered.
>>
>> "Counter values" may be allocated via iio_counter_value structures, and
>> respective "counter signal" associations made via iio_counter_trigger
>> structures. Initial associated iio_counter_trigger structures may be
>> stored as an array and set to the the init_triggers member of the
>> respective iio_counter_value structure. These iio_counter_value
>> structures may be set to the init_values member of an allocated
>> iio_counter structure before the counter is registered if so desired.
>>
>> A counter device is registered to the system by passing the respective
>> initialized iio_counter structure to the iio_counter_register function;
>> similarly, the iio_counter_unregister function unregisters the
>> respective counter.
>>
>> Signed-off-by: William Breathitt Gray <[e-mail]>
>
>Hi William,
>
>Thanks for your patches, I start try to implement them in stm32-timer driver
>but I think it will take me some time before understand all your code.
>
>I have some warning when compiling the code (see below).

Hi Benjamin,

Thank you for trying out the patches. I've been focusing on the main API
documentation thus far, so unfortunately the current code is still a bit
hard to follow -- hopefully I can clean it up some soon. Regardless,
I'll be happy to answer any questions you may encounter while reviewing
the patches.

Regarding the compilation warnings: see my response inline below.

>
>About wording, I think that using "trigger" to describe signal active
>states/edges
>could be confusing in IIO context but I haven't found yet a better name.

I agree very much with this. "Trigger" was a bad name choice when I
developed the Generic Counter paradigm. I would like to come up with a
better name for this component before this patchset is merged.

The "Trigger" component essentially describes an association between a
Signal and Value. The association typically has a defined Signal data
condition which triggers the respective Value function operation (or
occasionally the trigger condition is just left as "None"), but
ultimately it's the association itself that is the key aspect this
component.

I have considered changing it to "Association" or "Connection" as the
name, but both of these seem to sound too vague of terms. I shall keep
thinking of various alternative names for this component and change the
documentation in a subsequent patchset version once we have a more
fitting name.

>
>I also not very sure about what you expect from iio_counter_ops signal_read and
>signal_write functions, do you think get/set the value of the signal ?
>(i.e read gpio level ?)

Yes, for an ordinary simple counter, signal_read and signal_write would
typically expose control of the respective hardware input line level.

However, it is important to remember that within the context of the
Generic Counter paradigm, Signals are abstract components: a single
Signal may not directly correlate to a single hardware input line; this
is the primary reason for providing the signal_read/signal_write
functions.

For example, suppose we have a counter with a single Value associated to
a single Signal. The Signal data is a 3-bit decimal value, and the Value
is an ongoing count of the number of times the Signal data decimal value
has had a value greater than "5."

The hardware itself could consist of three individual input lines
(one for each bit), but there is ultimately only one Signal. In this
scenario, I would expect signal_read to simply return the 3-bit decimal
value -- not the three physical hardware input line level. Notice the
abstraction which has occurred: the Signal is the data represented by
the hardware input, but not the raw hardware input itself.

Sincerely,

William Breathitt Gray

>
>I will continue to review and implement your patches, I hope that end
>of next week
>have something functionnal to share with you.
>
>Thansk to have propose this, I do believe it will be helpful
>
>Benjamin
>> ---
>>  MAINTAINERS                        |    7 +
>>  drivers/iio/Kconfig                |    8 +
>>  drivers/iio/Makefile               |    1 +
>>  drivers/iio/counter/Kconfig        |    1 +
>>  drivers/iio/industrialio-counter.c | 1151 ++++++++++++++++++++++++++++++++++++
>>  include/linux/iio/counter.h        |  221 +++++++
>>  6 files changed, 1389 insertions(+)
>>  create mode 100644 drivers/iio/industrialio-counter.c
>>  create mode 100644 include/linux/iio/counter.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 6f7721d1634c..24fc2dcf1995 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -6577,6 +6577,13 @@ F:       Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>>  F:     Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
>>  F:     drivers/iio/adc/envelope-detector.c
>>
>> +IIO GENERIC COUNTER INTERFACE
>> +M:     William Breathitt Gray <[e-mail]>
>> +L:     [e-mail]
>> +S:     Maintained
>> +F:     drivers/iio/industrialio-counter.c
>> +F:     include/linux/iio/counter.h
>> +
>>  IIO MULTIPLEXER
>>  M:     Peter Rosin <[e-mail]>
>>  L:     [e-mail]
>> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
>> index b3c8c6ef0dff..78e01f4f5937 100644
>> --- a/drivers/iio/Kconfig
>> +++ b/drivers/iio/Kconfig
>> @@ -30,6 +30,14 @@ config IIO_CONFIGFS
>>           (e.g. software triggers). For more info see
>>           Documentation/iio/iio_configfs.txt.
>>
>> +config IIO_COUNTER
>> +       bool "Enable IIO counter support"
>> +       help
>> +         Provides IIO core support for counters. This API provides
>> +         a generic interface that serves as the building blocks to
>> +         create more complex counter interfaces. Rudimentary support
>> +         for counters is enabled.
>> +
>>  config IIO_TRIGGER
>>         bool "Enable triggered sampling support"
>>         help
>> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
>> index 93c769cd99bf..6427ff38f964 100644
>> --- a/drivers/iio/Makefile
>> +++ b/drivers/iio/Makefile
>> @@ -5,6 +5,7 @@
>>  obj-$(CONFIG_IIO) += industrialio.o
>>  industrialio-y := industrialio-core.o industrialio-event.o inkern.o
>>  industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
>> +industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
>>  industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
>>
>>  obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
>> diff --git a/drivers/iio/counter/Kconfig b/drivers/iio/counter/Kconfig
>> index b37e5fc03149..3d46a790d8db 100644
>> --- a/drivers/iio/counter/Kconfig
>> +++ b/drivers/iio/counter/Kconfig
>> @@ -4,6 +4,7 @@
>>  # When adding new entries keep the list in alphabetical order
>>
>>  menu "Counters"
>> +       depends on IIO_COUNTER
>>
>>  config 104_QUAD_8
>>         tristate "ACCES 104-QUAD-8 driver"
>> diff --git a/drivers/iio/industrialio-counter.c b/drivers/iio/industrialio-counter.c
>> new file mode 100644
>> index 000000000000..bdf190d010e4
>> --- /dev/null
>> +++ b/drivers/iio/industrialio-counter.c
>> @@ -0,0 +1,1151 @@
>> +/*
>> + * Industrial I/O counter interface functions
>> + * Copyright (C) 2017 William Breathitt Gray
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License, version 2, as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + */
>> +#include <linux/err.h>
>> +#include <linux/export.h>
>> +#include <linux/gfp.h>
>> +#include <linux/kernel.h>
>> +#include <linux/list.h>
>> +#include <linux/mutex.h>
>> +#include <linux/printk.h>
>> +#include <linux/slab.h>
>> +#include <linux/string.h>
>> +
>> +#include <linux/iio/iio.h>
>> +#include <linux/iio/types.h>
>> +
>> +#include <linux/iio/counter.h>
>> +
>> +static struct iio_counter_signal *iio_counter_signal_find_by_id(
>> +       const struct iio_counter *const counter, const int id)
>> +{
>> +       struct iio_counter_signal *iter;
>> +
>> +       list_for_each_entry(iter, &counter->signal_list, list)
>> +               if (iter->id == id)
>> +                       return iter;
>> +
>> +       return NULL;
>> +}
>> +
>> +static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
>> +       const struct iio_counter_value *const value, const int id)
>> +{
>> +       struct iio_counter_trigger *iter;
>> +
>> +       list_for_each_entry(iter, &value->trigger_list, list)
>> +               if (iter->signal->id == id)
>> +                       return iter;
>> +
>> +       return NULL;
>> +}
>> +
>> +static struct iio_counter_value *iio_counter_value_find_by_id(
>> +       const struct iio_counter *const counter, const int id)
>> +{
>> +       struct iio_counter_value *iter;
>> +
>> +       list_for_each_entry(iter, &counter->value_list, list)
>> +               if (iter->id == id)
>> +                       return iter;
>> +
>> +       return NULL;
>> +}
>> +
>> +static void iio_counter_trigger_unregister_all(
>> +       struct iio_counter_value *const value)
>> +{
>> +       struct iio_counter_trigger *iter, *tmp_iter;
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +       list_for_each_entry_safe(iter, tmp_iter, &value->trigger_list, list)
>> +               list_del(&iter->list);
>> +       mutex_unlock(&value->trigger_list_lock);
>> +}
>> +
>> +static void iio_counter_signal_unregister_all(struct iio_counter *const counter)
>> +{
>> +       struct iio_counter_signal *iter, *tmp_iter;
>> +
>> +       mutex_lock(&counter->signal_list_lock);
>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->signal_list, list)
>> +               list_del(&iter->list);
>> +       mutex_unlock(&counter->signal_list_lock);
>> +}
>> +
>> +static void iio_counter_value_unregister_all(struct iio_counter *const counter)
>> +{
>> +       struct iio_counter_value *iter, *tmp_iter;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->value_list, list) {
>> +               iio_counter_trigger_unregister_all(iter);
>> +
>> +               list_del(&iter->list);
>> +       }
>> +       mutex_unlock(&counter->value_list_lock);
>> +}
>> +
>> +static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       const struct iio_counter_signal *signal;
>> +
>> +       mutex_lock(&counter->signal_list_lock);
>> +       signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>> +       mutex_unlock(&counter->signal_list_lock);
>> +       if (!signal)
>> +               return -EINVAL;
>> +
>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
>> +}
>> +
>> +static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,
>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       const struct iio_counter_value *value;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       mutex_unlock(&counter->value_list_lock);
>> +       if (!value)
>> +               return -EINVAL;
>> +
>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", value->name);
>> +}
>> +
>> +static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       const struct iio_counter_trigger *trigger;
>> +       ssize_t len = 0;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               len = -EINVAL;
>> +               goto err_find_value;
>> +       }
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +       list_for_each_entry(trigger, &value->trigger_list, list) {
>> +               len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
>> +                       trigger->signal->id, trigger->signal->name,
>> +                       trigger->trigger_modes[trigger->mode]);
>> +               if (len >= PAGE_SIZE) {
>> +                       len = -ENOMEM;
>> +                       goto err_no_buffer_space;
>> +               }
>> +       }
>> +err_no_buffer_space:
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +err_find_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return len;
>> +}
>> +
>> +static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       ssize_t ret;
>> +       struct iio_counter_trigger *trigger;
>> +       const int signal_id = *(int *)((void *)priv);
>> +       int mode;
>> +
>> +       if (!counter->ops->trigger_mode_get)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               ret = -EINVAL;
>> +               goto err_value;
>> +       }
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +
>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>> +       if (!trigger) {
>> +               ret = -EINVAL;
>> +               goto err_trigger;
>> +       }
>> +
>> +       mode = counter->ops->trigger_mode_get(counter, value, trigger);
>> +
>> +       if (mode < 0) {
>> +               ret = mode;
>> +               goto err_trigger;
>> +       } else if (mode >= trigger->num_trigger_modes) {
>> +               ret = -EINVAL;
>> +               goto err_trigger;
>> +       }
>> +
>> +       trigger->mode = mode;
>> +
>> +       ret = scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
>> +
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return ret;
>> +
>> +err_trigger:
>> +       mutex_unlock(&value->trigger_list_lock);
>> +err_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +       return ret;
>> +}
>> +
>> +static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
>> +       uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
>> +       size_t len)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       ssize_t err;
>> +       struct iio_counter_trigger *trigger;
>> +       const int signal_id = *(int *)((void *)priv);
>> +       unsigned int mode;
>> +
>> +       if (!counter->ops->trigger_mode_set)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               err = -EINVAL;
>> +               goto err_value;
>> +       }
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +
>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>> +       if (!trigger) {
>> +               err = -EINVAL;
>> +               goto err_trigger;
>> +       }
>> +
>> +       for (mode = 0; mode < trigger->num_trigger_modes; mode++)
>> +               if (sysfs_streq(buf, trigger->trigger_modes[mode]))
>> +                       break;
>> +
>> +       if (mode >= trigger->num_trigger_modes) {
>> +               err = -EINVAL;
>> +               goto err_trigger;
>> +       }
>> +
>> +       err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
>> +       if (err)
>> +               goto err_trigger;
>> +
>> +       trigger->mode = mode;
>> +
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return len;
>> +
>> +err_trigger:
>> +       mutex_unlock(&value->trigger_list_lock);
>> +err_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +       return err;
>> +}
>> +
>> +static ssize_t iio_counter_trigger_mode_available_read(
>> +       struct iio_dev *indio_dev, uintptr_t priv,
>> +       const struct iio_chan_spec *chan, char *buf)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       ssize_t len = 0;
>> +       struct iio_counter_trigger *trigger;
>> +       const int signal_id = *(int *)((void *)priv);
>> +       unsigned int i;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               len = -EINVAL;
>> +               goto err_no_value;
>> +       }
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +
>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>> +       if (!trigger) {
>> +               len = -EINVAL;
>> +               goto err_no_trigger;
>> +       }
>> +
>> +       for (i = 0; i < trigger->num_trigger_modes; i++)
>> +               len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
>> +                       trigger->trigger_modes[i]);
>> +
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       buf[len - 1] = '\n';
>> +
>> +       return len;
>> +
>> +err_no_trigger:
>> +       mutex_unlock(&value->trigger_list_lock);
>> +err_no_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +       return len;
>> +}
>> +
>> +static int iio_counter_value_function_set(struct iio_dev *indio_dev,
>> +       const struct iio_chan_spec *chan, unsigned int mode)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       int err;
>> +
>> +       if (!counter->ops->value_function_set)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               err = -EINVAL;
>> +               goto err_value;
>> +       }
>> +
>> +       err = counter->ops->value_function_set(counter, value, mode);
>> +       if (err)
>> +               goto err_value;
>> +
>> +       value->mode = mode;
>> +
>> +err_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return err;
>> +}
>> +
>> +static int iio_counter_value_function_get(struct iio_dev *indio_dev,
>> +       const struct iio_chan_spec *chan)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_value *value;
>> +       int retval;
>> +
>> +       if (!counter->ops->value_function_get)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +       if (!value) {
>> +               retval = -EINVAL;
>> +               goto err_value;
>> +       }
>> +
>> +       retval = counter->ops->value_function_get(counter, value);
>> +       if (retval < 0)
>> +               goto err_value;
>> +       else if (retval >= value->num_function_modes) {
>> +               retval = -EINVAL;
>> +               goto err_value;
>> +       }
>> +
>> +       value->mode = retval;
>> +
>> +err_value:
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return retval;
>> +}
>> +
>> +static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
>> +       struct iio_counter_value *const value)
>> +{
>> +       const struct iio_chan_spec_ext_info ext_info_default[] = {
>> +               {
>> +                       .name = "name",
>> +                       .shared = IIO_SEPARATE,
>> +                       .read = iio_counter_value_name_read
>> +               },
>> +               IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
>> +               {
>> +                       .name = "function_available",
>> +                       .shared = IIO_SEPARATE,
>> +                       .read = iio_enum_available_read,
>> +                       .private = (void *)&value->function_enum
>I have this warning the 3 times that  private field is set
>drivers/iio/industrialio-counter.c:401:15: warning: initialization
>makes integer from pointer without a cast [-Wint-conversion]
>    .private = (void *)&value->function_enum
>
>I think you can change it to "void *" instead of a uintptr_t

These are pretty benign warnings which you may ignore: I'm doing an
implicit conversion to uintptr_t which is ultimately an integer type; in
general, pointer to integer conversations are unsafe, but there is a
special exception in the C language for the uintptr_t data type. I could
have used an explicit cast to avoid the warning but opted to leave it
implicit to keep the code easier to read.

However, it would be nice if the private member was void *, since the
intent of my code would be clearer in that case (passing a pointer for
later dereference). Unfortunately, I'm hesitant to submit a patch to
change the "private" member data type to void * since other drivers may
require the uintptr_t data type -- my suspicion is that there are some
drivers out there which do since the choice to introduce the "private"
member as a uintptr_t appears deliberate.

>> +               },
>> +               {
>> +                       .name = "triggers",
>> +                       .shared = IIO_SEPARATE,
>> +                       .read = iio_counter_value_triggers_read
>> +               }
>> +       };
>> +       const size_t num_default = ARRAY_SIZE(ext_info_default);
>> +       const struct iio_chan_spec_ext_info ext_info_trigger[] = {
>> +               {
>> +                       .shared = IIO_SEPARATE,
>> +                       .read = iio_counter_trigger_mode_read,
>> +                       .write = iio_counter_trigger_mode_write
>> +               },
>> +               {
>> +                       .shared = IIO_SEPARATE,
>> +                       .read = iio_counter_trigger_mode_available_read
>> +               }
>> +       };
>> +       const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
>> +       const struct list_head *pos;
>> +       size_t num_triggers = 0;
>> +       size_t num_triggers_ext_info;
>> +       size_t num_ext_info;
>> +       int err;
>> +       struct iio_chan_spec_ext_info *ext_info;
>> +       const struct iio_counter_trigger *trigger_pos;
>> +       size_t i;
>> +
>> +       value->function_enum.items = value->function_modes;
>> +       value->function_enum.num_items = value->num_function_modes;
>> +       value->function_enum.set = iio_counter_value_function_set;
>> +       value->function_enum.get = iio_counter_value_function_get;
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +
>> +       list_for_each(pos, &value->trigger_list)
>> +               num_triggers++;
>> +
>> +       num_triggers_ext_info = num_ext_info_trigger * num_triggers;
>> +       num_ext_info = num_default + num_triggers_ext_info + 1;
>> +
>> +       ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
>> +       if (!ext_info) {
>> +               err = -ENOMEM;
>> +               goto err_ext_info_alloc;
>> +       }
>> +       ext_info[num_ext_info - 1].name = NULL;
>> +
>> +       memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
>> +       for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
>> +               memcpy(ext_info + num_default + i, ext_info_trigger,
>> +                       sizeof(ext_info_trigger));
>> +
>> +       i = num_default;
>> +       list_for_each_entry(trigger_pos, &value->trigger_list, list) {
>> +               ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
>> +                       chan->channel, trigger_pos->signal->id);
>> +               if (!ext_info[i].name) {
>> +                       err = -ENOMEM;
>> +                       goto err_name_alloc;
>> +               }
>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>> +               i++;
>> +
>> +               ext_info[i].name = kasprintf(GFP_KERNEL,
>> +                       "trigger_signal%d-%d_available",
>> +                       chan->channel, trigger_pos->signal->id);
>> +               if (!ext_info[i].name) {
>> +                       err = -ENOMEM;
>> +                       goto err_name_alloc;
>> +               }
>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>> +               i++;
>> +       }
>> +
>> +       chan->ext_info = ext_info;
>> +
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +       return 0;
>> +
>> +err_name_alloc:
>> +       while (i-- > num_default)
>> +               kfree(ext_info[i].name);
>> +       kfree(ext_info);
>> +err_ext_info_alloc:
>> +       mutex_unlock(&value->trigger_list_lock);
>> +       return err;
>> +}
>> +
>> +static void iio_counter_value_ext_info_free(
>> +       const struct iio_chan_spec *const channel)
>> +{
>> +       size_t i;
>> +       const char *const prefix = "trigger_signal";
>> +       const size_t prefix_len = strlen(prefix);
>> +
>> +       for (i = 0; channel->ext_info[i].name; i++)
>> +               if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
>> +                       kfree(channel->ext_info[i].name);
>> +       kfree(channel->ext_info);
>> +}
>> +
>> +static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
>> +       {
>> +               .name = "name",
>> +               .shared = IIO_SEPARATE,
>> +               .read = iio_counter_signal_name_read
>> +       },
>> +       {}
>> +};
>> +
>> +static int iio_counter_channels_alloc(struct iio_counter *const counter)
>> +{
>> +       const struct list_head *pos;
>> +       size_t num_channels = 0;
>> +       int err;
>> +       struct iio_chan_spec *channels;
>> +       struct iio_counter_value *value_pos;
>> +       size_t i = counter->num_channels;
>> +       const struct iio_counter_signal *signal_pos;
>> +
>> +       mutex_lock(&counter->signal_list_lock);
>> +
>> +       list_for_each(pos, &counter->signal_list)
>> +               num_channels++;
>> +
>> +       if (!num_channels) {
>> +               err = -EINVAL;
>> +               goto err_no_signals;
>> +       }
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +
>> +       list_for_each(pos, &counter->value_list)
>> +               num_channels++;
>> +
>> +       num_channels += counter->num_channels;
>> +
>> +       channels = kcalloc(num_channels, sizeof(*channels), GFP_KERNEL);
>> +       if (!channels) {
>> +               err = -ENOMEM;
>> +               goto err_channels_alloc;
>> +       }
>> +
>> +       memcpy(channels, counter->channels,
>> +               counter->num_channels * sizeof(*counter->channels));
>> +
>> +       list_for_each_entry(value_pos, &counter->value_list, list) {
>> +               channels[i].type = IIO_COUNT;
>> +               channels[i].channel = counter->id;
>> +               channels[i].channel2 = value_pos->id;
>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>> +               channels[i].indexed = 1;
>> +               channels[i].counter = 1;
>> +
>> +               err = iio_counter_value_ext_info_alloc(channels + i, value_pos);
>> +               if (err)
>> +                       goto err_value_ext_info_alloc;
>> +
>> +               i++;
>> +       }
>> +
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       list_for_each_entry(signal_pos, &counter->signal_list, list) {
>> +               channels[i].type = IIO_SIGNAL;
>> +               channels[i].channel = counter->id;
>> +               channels[i].channel2 = signal_pos->id;
>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>> +               channels[i].indexed = 1;
>> +               channels[i].counter = 1;
>> +               channels[i].ext_info = iio_counter_signal_ext_info;
>> +
>> +               i++;
>> +       }
>> +
>> +       mutex_unlock(&counter->signal_list_lock);
>> +
>> +       counter->indio_dev->num_channels = num_channels;
>> +       counter->indio_dev->channels = channels;
>> +
>> +       return 0;
>> +
>> +err_value_ext_info_alloc:
>> +       while (i-- > counter->num_channels)
>> +               iio_counter_value_ext_info_free(channels + i);
>> +       kfree(channels);
>> +err_channels_alloc:
>> +       mutex_unlock(&counter->value_list_lock);
>> +err_no_signals:
>> +       mutex_unlock(&counter->signal_list_lock);
>> +       return err;
>> +}
>> +
>> +static void iio_counter_channels_free(const struct iio_counter *const counter)
>> +{
>> +       size_t i = counter->num_channels + counter->indio_dev->num_channels;
>> +       const struct iio_chan_spec *const chans = counter->indio_dev->channels;
>> +
>> +       while (i-- > counter->num_channels)
>> +               if (chans[i].type == IIO_COUNT)
>> +                       iio_counter_value_ext_info_free(chans + i);
>> +
>> +       kfree(chans);
>> +}
>> +
>> +static int iio_counter_read_raw(struct iio_dev *indio_dev,
>> +       struct iio_chan_spec const *chan, int *val, int *val2, long mask)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_signal *signal;
>> +       int retval;
>> +       struct iio_counter_value *value;
>> +
>> +       if (mask != IIO_CHAN_INFO_RAW)
>> +               return -EINVAL;
>> +
>> +       switch (chan->type) {
>> +       case IIO_SIGNAL:
>> +               if (!counter->ops->signal_read)
>> +                       return -EINVAL;
>> +
>> +               mutex_lock(&counter->signal_list_lock);
>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>> +               if (!signal) {
>> +                       mutex_unlock(&counter->signal_list_lock);
>> +                       return -EINVAL;
>> +               }
>> +
>> +               retval = counter->ops->signal_read(counter, signal, val, val2);
>> +               mutex_unlock(&counter->signal_list_lock);
>> +
>> +               return retval;
>> +       case IIO_COUNT:
>> +               if (!counter->ops->value_read)
>> +                       return -EINVAL;
>> +
>> +               mutex_lock(&counter->value_list_lock);
>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +               if (!value) {
>> +                       mutex_unlock(&counter->value_list_lock);
>> +                       return -EINVAL;
>> +               }
>> +
>> +               retval = counter->ops->value_read(counter, value, val, val2);
>> +               mutex_unlock(&counter->value_list_lock);
>> +
>> +               return retval;
>> +       default:
>> +               if (counter->info && counter->info->read_raw)
>> +                       return counter->info->read_raw(indio_dev, chan, val,
>> +                               val2, mask);
>> +       }
>> +
>> +       return -EINVAL;
>> +}
>> +
>> +static int iio_counter_write_raw(struct iio_dev *indio_dev,
>> +       struct iio_chan_spec const *chan, int val, int val2, long mask)
>> +{
>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>> +       struct iio_counter_signal *signal;
>> +       int retval;
>> +       struct iio_counter_value *value;
>> +
>> +       if (mask != IIO_CHAN_INFO_RAW)
>> +               return -EINVAL;
>> +
>> +       switch (chan->type) {
>> +       case IIO_SIGNAL:
>> +               if (!counter->ops->signal_write)
>> +                       return -EINVAL;
>> +
>> +               mutex_lock(&counter->signal_list_lock);
>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>> +               if (!signal) {
>> +                       mutex_unlock(&counter->signal_list_lock);
>> +                       return -EINVAL;
>> +               }
>> +
>> +               retval = counter->ops->signal_write(counter, signal, val, val2);
>> +               mutex_unlock(&counter->signal_list_lock);
>> +
>> +               return retval;
>> +       case IIO_COUNT:
>> +               if (!counter->ops->value_write)
>> +                       return -EINVAL;
>> +
>> +               mutex_lock(&counter->value_list_lock);
>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>> +               if (!value) {
>> +                       mutex_unlock(&counter->value_list_lock);
>> +                       return -EINVAL;
>> +               }
>> +
>> +               retval = counter->ops->value_write(counter, value, val, val2);
>> +               mutex_unlock(&counter->value_list_lock);
>> +
>> +               return retval;
>> +       default:
>> +               if (counter->info && counter->info->write_raw)
>> +                       return counter->info->write_raw(indio_dev, chan, val,
>> +                               val2, mask);
>> +       }
>> +
>> +       return -EINVAL;
>> +}
>> +
>> +static int iio_counter_signal_register(struct iio_counter *const counter,
>> +       struct iio_counter_signal *const signal)
>> +{
>> +       int err;
>> +
>> +       if (!counter || !signal)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&counter->signal_list_lock);
>> +       if (iio_counter_signal_find_by_id(counter, signal->id)) {
>> +               pr_err("Duplicate counter signal ID '%d'\n", signal->id);
>> +               err = -EEXIST;
>> +               goto err_duplicate_id;
>> +       }
>> +       list_add_tail(&signal->list, &counter->signal_list);
>> +       mutex_unlock(&counter->signal_list_lock);
>> +
>> +       return 0;
>> +
>> +err_duplicate_id:
>> +       mutex_unlock(&counter->signal_list_lock);
>> +       return err;
>> +}
>> +
>> +static void iio_counter_signal_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_signal *const signal)
>> +{
>> +       if (!counter || !signal)
>> +               return;
>> +
>> +       mutex_lock(&counter->signal_list_lock);
>> +       list_del(&signal->list);
>> +       mutex_unlock(&counter->signal_list_lock);
>> +}
>> +
>> +static int iio_counter_signals_register(struct iio_counter *const counter,
>> +       struct iio_counter_signal *const signals, const size_t num_signals)
>> +{
>> +       size_t i;
>> +       int err;
>> +
>> +       if (!counter || !signals)
>> +               return -EINVAL;
>> +
>> +       for (i = 0; i < num_signals; i++) {
>> +               err = iio_counter_signal_register(counter, signals + i);
>> +               if (err)
>> +                       goto err_signal_register;
>> +       }
>> +
>> +       return 0;
>> +
>> +err_signal_register:
>> +       while (i--)
>> +               iio_counter_signal_unregister(counter, signals + i);
>> +       return err;
>> +}
>> +
>> +static void iio_counter_signals_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_signal *signals, size_t num_signals)
>> +{
>> +       if (!counter || !signals)
>> +               return;
>> +
>> +       while (num_signals--) {
>> +               iio_counter_signal_unregister(counter, signals);
>> +               signals++;
>> +       }
>> +}
>> +
>> +/**
>> + * iio_counter_trigger_register - register Trigger to Value
>> + * @value: pointer to IIO Counter Value for association
>> + * @trigger: pointer to IIO Counter Trigger to register
>> + *
>> + * The Trigger is added to the Value's trigger_list. A check is first performed
>> + * to verify that the respective Signal is not already linked to the Value; if
>> + * the respective Signal is already linked to the Value, the Trigger is not
>> + * added to the Value's trigger_list.
>> + *
>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>> + * during execution.
>> + */
>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const trigger)
>> +{
>> +       if (!value || !trigger || !trigger->signal)
>> +               return -EINVAL;
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +       if (iio_counter_trigger_find_by_id(value, trigger->signal->id)) {
>> +               pr_err("Signal%d is already linked to counter value%d\n",
>> +                       trigger->signal->id, value->id);
>> +               return -EEXIST;
>> +       }
>> +       list_add_tail(&trigger->list, &value->trigger_list);
>> +       mutex_unlock(&value->trigger_list_lock);
>> +
>> +       return 0;
>> +}
>> +EXPORT_SYMBOL(iio_counter_trigger_register);
>> +
>> +/**
>> + * iio_counter_trigger_unregister - unregister Trigger from Value
>> + * @value: pointer to IIO Counter Value of association
>> + * @trigger: pointer to IIO Counter Trigger to unregister
>> + *
>> + * The Trigger is removed from the Value's trigger_list.
>> + *
>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>> + * during execution.
>> + */
>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const trigger)
>> +{
>> +       if (!value || !trigger || !trigger->signal)
>> +               return;
>> +
>> +       mutex_lock(&value->trigger_list_lock);
>> +       list_del(&trigger->list);
>> +       mutex_unlock(&value->trigger_list_lock);
>> +}
>> +EXPORT_SYMBOL(iio_counter_trigger_unregister);
>> +
>> +/**
>> + * iio_counter_triggers_register - register an array of Triggers to Value
>> + * @value: pointer to IIO Counter Value for association
>> + * @triggers: array of pointers to IIO Counter Triggers to register
>> + *
>> + * The iio_counter_trigger_register function is called for each Trigger in the
>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>> + *
>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>> + */
>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers)
>> +{
>> +       size_t i;
>> +       int err;
>> +
>> +       if (!value || !triggers)
>> +               return -EINVAL;
>> +
>> +       for (i = 0; i < num_triggers; i++) {
>> +               err = iio_counter_trigger_register(value, triggers + i);
>> +               if (err)
>> +                       goto err_trigger_register;
>> +       }
>> +
>> +       return 0;
>> +
>> +err_trigger_register:
>> +       while (i--)
>> +               iio_counter_trigger_unregister(value, triggers + i);
>> +       return err;
>> +}
>> +EXPORT_SYMBOL(iio_counter_triggers_register);
>> +
>> +/**
>> + * iio_counter_triggers_unregister - unregister Triggers from Value
>> + * @value: pointer to IIO Counter Value of association
>> + * @triggers: array of pointers to IIO Counter Triggers to unregister
>> + *
>> + * The iio_counter_trigger_unregister function is called for each Trigger in the
>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>> + *
>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>> + */
>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *triggers, size_t num_triggers)
>> +{
>> +       if (!value || !triggers)
>> +               return;
>> +
>> +       while (num_triggers--) {
>> +               iio_counter_trigger_unregister(value, triggers);
>> +               triggers++;
>> +       }
>> +}
>> +EXPORT_SYMBOL(iio_counter_triggers_unregister);
>> +
>> +/**
>> + * iio_counter_value_register - register Value to Counter
>> + * @counter: pointer to IIO Counter for association
>> + * @value: pointer to IIO Counter Value to register
>> + *
>> + * The registration process occurs in two major steps. First, the Value is
>> + * initialized: trigger_list_lock is initialized, trigger_list is initialized,
>> + * and init_triggers if not NULL is passed to iio_counter_triggers_register.
>> + * Second, the Value is added to the Counter's value_list. A check is first
>> + * performed to verify that the Value is not already associated to the Counter
>> + * (via the Value's unique ID); if the Value is already associated to the
>> + * Counter, the Value is not added to the Counter's value_list and all of the
>> + * Value's Triggers are unregistered.
>> + *
>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>> + * during execution.
>> + */
>> +int iio_counter_value_register(struct iio_counter *const counter,
>> +       struct iio_counter_value *const value)
>> +{
>> +       int err;
>> +
>> +       if (!counter || !value)
>> +               return -EINVAL;
>> +
>> +       mutex_init(&value->trigger_list_lock);
>> +       INIT_LIST_HEAD(&value->trigger_list);
>> +
>> +       if (value->init_triggers) {
>> +               err = iio_counter_triggers_register(value,
>> +                       value->init_triggers, value->num_init_triggers);
>> +               if (err)
>> +                       return err;
>> +       }
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +       if (iio_counter_value_find_by_id(counter, value->id)) {
>> +               pr_err("Duplicate counter value ID '%d'\n", value->id);
>> +               err = -EEXIST;
>> +               goto err_duplicate_id;
>> +       }
>> +       list_add_tail(&value->list, &counter->value_list);
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       return 0;
>> +
>> +err_duplicate_id:
>> +       mutex_unlock(&counter->value_list_lock);
>> +       iio_counter_trigger_unregister_all(value);
>> +       return err;
>> +}
>> +EXPORT_SYMBOL(iio_counter_value_register);
>> +
>> +/**
>> + * iio_counter_value_unregister - unregister Value from Counter
>> + * @counter: pointer to IIO Counter of association
>> + * @value: pointer to IIO Counter Value to unregister
>> + *
>> + * The Value is removed from the Counter's value_list and all of the Value's
>> + * Triggers are unregistered.
>> + *
>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>> + * during execution.
>> + */
>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_value *const value)
>> +{
>> +       if (!counter || !value)
>> +               return;
>> +
>> +       mutex_lock(&counter->value_list_lock);
>> +       list_del(&value->list);
>> +       mutex_unlock(&counter->value_list_lock);
>> +
>> +       iio_counter_trigger_unregister_all(value);
>> +}
>> +EXPORT_SYMBOL(iio_counter_value_unregister);
>> +
>> +/**
>> + * iio_counter_values_register - register an array of Values to Counter
>> + * @counter: pointer to IIO Counter for association
>> + * @values: array of pointers to IIO Counter Values to register
>> + *
>> + * The iio_counter_value_register function is called for each Value in the
>> + * array. The @values array is traversed for the first @num_values Values.
>> + *
>> + * NOTE: @num_values must not be greater than the size of the @values array.
>> + */
>> +int iio_counter_values_register(struct iio_counter *const counter,
>> +       struct iio_counter_value *const values, const size_t num_values)
>> +{
>> +       size_t i;
>> +       int err;
>> +
>> +       if (!counter || !values)
>> +               return -EINVAL;
>> +
>> +       for (i = 0; i < num_values; i++) {
>> +               err = iio_counter_value_register(counter, values + i);
>> +               if (err)
>> +                       goto err_values_register;
>> +       }
>> +
>> +       return 0;
>> +
>> +err_values_register:
>> +       while (i--)
>> +               iio_counter_value_unregister(counter, values + i);
>> +       return err;
>> +}
>> +EXPORT_SYMBOL(iio_counter_values_register);
>> +
>> +/**
>> + * iio_counter_values_unregister - unregister Values from Counter
>> + * @counter: pointer to IIO Counter of association
>> + * @values: array of pointers to IIO Counter Values to unregister
>> + *
>> + * The iio_counter_value_unregister function is called for each Value in the
>> + * array. The @values array is traversed for the first @num_values Values.
>> + *
>> + * NOTE: @num_values must not be greater than the size of the @values array.
>> + */
>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_value *values, size_t num_values)
>> +{
>> +       if (!counter || !values)
>> +               return;
>> +
>> +       while (num_values--) {
>> +               iio_counter_value_unregister(counter, values);
>> +               values++;
>> +       }
>> +}
>> +EXPORT_SYMBOL(iio_counter_values_unregister);
>> +
>> +/**
>> + * iio_counter_register - register Counter to the system
>> + * @counter: pointer to IIO Counter to register
>> + *
>> + * This function piggybacks off of iio_device_register. First, the relevant
>> + * Counter members are initialized; if init_signals is not NULL it is passed to
>> + * iio_counter_signals_register, and similarly if init_values is not NULL it is
>> + * passed to iio_counter_values_register. Next, a struct iio_dev is allocated by
>> + * a call to iio_device_alloc and initialized for the Counter, IIO channels are
>> + * allocated, the Counter is copied as the private data, and finally
>> + * iio_device_register is called.
>> + */
>> +int iio_counter_register(struct iio_counter *const counter)
>> +{
>> +       const struct iio_info info_default = {
>> +               .read_raw = iio_counter_read_raw,
>> +               .write_raw = iio_counter_write_raw
>> +       };
>> +       int err;
>> +       struct iio_info *info;
>> +       struct iio_counter *priv;
>> +
>> +       if (!counter)
>> +               return -EINVAL;
>> +
>> +       mutex_init(&counter->signal_list_lock);
>> +       INIT_LIST_HEAD(&counter->signal_list);
>> +
>> +       if (counter->init_signals) {
>> +               err = iio_counter_signals_register(counter,
>> +                       counter->init_signals, counter->num_init_signals);
>> +               if (err)
>> +                       return err;
>> +       }
>> +
>> +       mutex_init(&counter->value_list_lock);
>> +       INIT_LIST_HEAD(&counter->value_list);
>> +
>> +       if (counter->init_values) {
>> +               err = iio_counter_values_register(counter,
>> +                       counter->init_values, counter->num_init_values);
>> +               if (err)
>> +                       goto err_values_register;
>> +       }
>> +
>> +       counter->indio_dev = iio_device_alloc(sizeof(*counter));
>> +       if (!counter->indio_dev) {
>> +               err = -ENOMEM;
>> +               goto err_iio_device_alloc;
>> +       }
>> +
>> +       info = kmalloc(sizeof(*info), GFP_KERNEL);
>> +       if (!info) {
>> +               err = -ENOMEM;
>> +               goto err_info_alloc;
>> +       }
>> +       if (counter->info) {
>> +               memcpy(info, counter->info, sizeof(*counter->info));
>> +               info->read_raw = iio_counter_read_raw;
>> +               info->write_raw = iio_counter_write_raw;
>> +       } else {
>> +               memcpy(info, &info_default, sizeof(info_default));
>> +       }
>> +
>> +       counter->indio_dev->info = info;
>> +       counter->indio_dev->modes = INDIO_DIRECT_MODE;
>> +       counter->indio_dev->name = counter->name;
>> +       counter->indio_dev->dev.parent = counter->dev;
>> +
>> +       err = iio_counter_channels_alloc(counter);
>> +       if (err)
>> +               goto err_channels_alloc;
>> +
>> +       priv = iio_priv(counter->indio_dev);
>> +       memcpy(priv, counter, sizeof(*priv));
>> +
>> +       err = iio_device_register(priv->indio_dev);
>> +       if (err)
>> +               goto err_iio_device_register;
>> +
>> +       return 0;
>> +
>> +err_iio_device_register:
>> +       iio_counter_channels_free(counter);
>> +err_channels_alloc:
>> +       kfree(info);
>> +err_info_alloc:
>> +       iio_device_free(counter->indio_dev);
>> +err_iio_device_alloc:
>> +       iio_counter_values_unregister(counter, counter->init_values,
>> +               counter->num_init_values);
>> +err_values_register:
>> +       iio_counter_signals_unregister(counter, counter->init_signals,
>> +               counter->num_init_signals);
>> +       return err;
>> +}
>> +EXPORT_SYMBOL(iio_counter_register);
>> +
>> +/**
>> + * iio_counter_unregister - unregister Counter from the system
>> + * @counter: pointer to IIO Counter to unregister
>> + *
>> + * The Counter is unregistered from the system. The indio_dev is unregistered,
>> + * allocated memory is freed, and all associated Values and Signals are
>> + * unregistered.
>> + */
>> +void iio_counter_unregister(struct iio_counter *const counter)
>> +{
>> +       const struct iio_info *const info = counter->indio_dev->info;
>> +
>> +       if (!counter)
>> +               return;
>> +
>> +       iio_device_unregister(counter->indio_dev);
>> +
>> +       iio_counter_channels_free(counter);
>> +
>> +       kfree(info);
>> +       iio_device_free(counter->indio_dev);
>> +
>> +       iio_counter_value_unregister_all(counter);
>> +       iio_counter_signal_unregister_all(counter);
>> +}
>> +EXPORT_SYMBOL(iio_counter_unregister);
>> diff --git a/include/linux/iio/counter.h b/include/linux/iio/counter.h
>> new file mode 100644
>> index 000000000000..1c1ca13a6053
>> --- /dev/null
>> +++ b/include/linux/iio/counter.h
>> @@ -0,0 +1,221 @@
>> +/*
>> + * Industrial I/O counter interface
>> + * Copyright (C) 2017 William Breathitt Gray
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License, version 2, as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + */
>> +#ifndef _IIO_COUNTER_H_
>> +#define _IIO_COUNTER_H_
>> +
>> +#ifdef CONFIG_IIO_COUNTER
>> +
>> +#include <linux/device.h>
>> +#include <linux/mutex.h>
>> +#include <linux/types.h>
>> +
>> +#include <linux/iio/iio.h>
>> +
>> +/**
>> + * struct iio_counter_signal - IIO Counter Signal node
>> + * @id:                [DRIVER] unique ID used to identify signal
>> + * @name:      [DRIVER] device-specific signal name
>> + * @list:      [INTERN] list of all signals currently registered to counter
>> + */
>> +struct iio_counter_signal {
>> +       int             id;
>> +       const char      *name;
>> +
>> +       struct list_head        list;
>> +};
>> +
>> +/**
>> + * struct iio_counter_trigger - IIO Counter Trigger node
>> + * @mode:              [DRIVER] current trigger mode state
>> + * @trigger_modes:     [DRIVER] available trigger modes
>> + * @num_trigger_modes: [DRIVER] number of modes specified in @trigger_modes
>> + * @signal:            [DRIVER] pointer to associated signal
>> + * @list:              [INTERN] list of all triggers currently registered to
>> + *                     value
>> + */
>> +struct iio_counter_trigger {
>> +       unsigned int                    mode;
>> +       const char *const               *trigger_modes;
>> +       unsigned int                    num_trigger_modes;
>> +       struct iio_counter_signal       *signal;
>> +
>> +       struct list_head                list;
>> +};
>> +
>> +/**
>> + * struct iio_counter_value - IIO Counter Value node
>> + * @id:                        [DRIVER] unique ID used to identify value
>> + * @name:              [DRIVER] device-specific value name
>> + * @mode:              [DRIVER] current function mode state
>> + * @function_modes:    [DRIVER] available function modes
>> + * @num_function_modes:        [DRIVER] number of modes specified in @function_modes
>> + * @init_triggers:     [DRIVER] array of triggers for initialization
>> + * @num_init_triggers: [DRIVER] number of triggers specified in @init_triggers
>> + * @function_enum:     [INTERN] used internally to generate function attributes
>> + * @trigger_list_lock: [INTERN] lock for accessing @trigger_list
>> + * @trigger_list:      [INTERN] list of all triggers currently registered to
>> + *                     value
>> + * @list:              [INTERN] list of all values currently registered to
>> + *                     counter
>> + */
>> +struct iio_counter_value {
>> +       int                     id;
>> +       const char              *name;
>> +       unsigned int            mode;
>> +       const char *const       *function_modes;
>> +       unsigned int            num_function_modes;
>> +
>> +       struct iio_counter_trigger      *init_triggers;
>> +       size_t                          num_init_triggers;
>> +
>> +       struct iio_enum         function_enum;
>> +       struct mutex            trigger_list_lock;
>> +       struct list_head        trigger_list;
>> +
>> +       struct list_head        list;
>> +};
>> +
>> +struct iio_counter;
>> +
>> +/**
>> + * struct iio_counter_ops - IIO Counter related callbacks
>> + * @signal_read:       function to request a signal value from the device.
>> + *                     Return value will specify the type of value returned by
>> + *                     the device. val and val2 will contain the elements
>> + *                     making up the returned value. Note that the counter
>> + *                     signal_list_lock is acquired before this function is
>> + *                     called, and released after this function returns.
>> + * @signal_write:      function to write a signal value to the device.
>> + *                     Parameters and locking behavior are the same as
>> + *                     signal_read.
>> + * @trigger_mode_set:  function to set the trigger mode. mode is the index of
>> + *                     the requested mode from the value trigger_modes array.
>> + *                     Note that the counter value_list_lock and value
>> + *                     trigger_list_lock are acquired before this function is
>> + *                     called, and released after this function returns.
>> + * @trigger_mode_get:  function to get the current trigger mode. Return value
>> + *                     will specify the index of the current mode from the
>> + *                     value trigger_modes array. Locking behavior is the same
>> + *                     as trigger_mode_set.
>> + * @value_read:                function to request a value value from the device.
>> + *                     Return value will specify the type of value returned by
>> + *                     the device. val and val2 will contain the elements
>> + *                     making up the returned value. Note that the counter
>> + *                     value_list_lock is acquired before this function is
>> + *                     called, and released after this function returns.
>> + * @value_write:       function to write a value value to the device.
>> + *                     Parameters and locking behavior are the same as
>> + *                     value_read.
>> + * @value_function_set: function to set the value function mode. mode is the
>> + *                     index of the requested mode from the value
>> + *                     function_modes array. Note that the counter
>> + *                     value_list_lock is acquired before this function is
>> + *                     called, and released after this function returns.
>> + * @value_function_get: function to get the current value function mode. Return
>> + *                     value will specify the index of the current mode from
>> + *                     the value function_modes array. Locking behavior is the
>> + *                     same as value_function_get.
>> + */
>> +struct iio_counter_ops {
>> +       int (*signal_read)(struct iio_counter *counter,
>> +               struct iio_counter_signal *signal, int *val, int *val2);
>> +       int (*signal_write)(struct iio_counter *counter,
>> +               struct iio_counter_signal *signal, int val, int val2);
>> +       int (*trigger_mode_set)(struct iio_counter *counter,
>> +               struct iio_counter_value *value,
>> +               struct iio_counter_trigger *trigger, unsigned int mode);
>> +       int (*trigger_mode_get)(struct iio_counter *counter,
>> +               struct iio_counter_value *value,
>> +               struct iio_counter_trigger *trigger);
>> +       int (*value_read)(struct iio_counter *counter,
>> +               struct iio_counter_value *value, int *val, int *val2);
>> +       int (*value_write)(struct iio_counter *counter,
>> +               struct iio_counter_value *value, int val, int val2);
>> +       int (*value_function_set)(struct iio_counter *counter,
>> +               struct iio_counter_value *value, unsigned int mode);
>> +       int (*value_function_get)(struct iio_counter *counter,
>> +               struct iio_counter_value *value);
>> +};
>> +
>> +/**
>> + * struct iio_counter - IIO Counter data structure
>> + * @id:                        [DRIVER] unique ID used to identify counter
>> + * @name:              [DRIVER] name of the device
>> + * @dev:               [DRIVER] device structure, should be assigned a parent
>> + *                     and owner
>> + * @ops:               [DRIVER] callbacks from driver for counter components
>> + * @init_signals:      [DRIVER] array of signals for initialization
>> + * @num_init_signals:  [DRIVER] number of signals specified in @init_signals
>> + * @init_values:       [DRIVER] array of values for initialization
>> + * @num_init_values:   [DRIVER] number of values specified in @init_values
>> + * @signal_list_lock:  [INTERN] lock for accessing @signal_list
>> + * @signal_list:       [INTERN] list of all signals currently registered to
>> + *                     counter
>> + * @value_list_lock:   [INTERN] lock for accessing @value_list
>> + * @value_list:                [INTERN] list of all values currently registered to
>> + *                     counter
>> + * @channels:          [DRIVER] channel specification structure table
>> + * @num_channels:      [DRIVER] number of channels specified in @channels
>> + * @info:              [DRIVER] callbacks and constant info from driver
>> + * @indio_dev:         [INTERN] industrial I/O device structure
>> + * @driver_data:       [DRIVER] driver data
>> + */
>> +struct iio_counter {
>> +       int                             id;
>> +       const char                      *name;
>> +       struct device                   *dev;
>> +       const struct iio_counter_ops    *ops;
>> +
>> +       struct iio_counter_signal       *init_signals;
>> +       size_t                          num_init_signals;
>> +       struct iio_counter_value        *init_values;
>> +       size_t                          num_init_values;
>> +
>> +       struct mutex            signal_list_lock;
>> +       struct list_head        signal_list;
>> +       struct mutex            value_list_lock;
>> +       struct list_head        value_list;
>> +
>> +       const struct iio_chan_spec      *channels;
>> +       size_t                          num_channels;
>> +       const struct iio_info           *info;
>> +
>> +       struct iio_dev  *indio_dev;
>> +       void            *driver_data;
>> +};
>> +
>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const trigger);
>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const trigger);
>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers);
>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>> +       struct iio_counter_trigger *triggers, size_t num_triggers);
>> +
>> +int iio_counter_value_register(struct iio_counter *const counter,
>> +       struct iio_counter_value *const value);
>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_value *const value);
>> +int iio_counter_values_register(struct iio_counter *const counter,
>> +       struct iio_counter_value *const values, const size_t num_values);
>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>> +       struct iio_counter_value *values, size_t num_values);
>> +
>> +int iio_counter_register(struct iio_counter *const counter);
>> +void iio_counter_unregister(struct iio_counter *const counter);
>> +
>> +#endif /* CONFIG_IIO_COUNTER */
>> +
>> +#endif /* _IIO_COUNTER_H_ */
>> --
>> 2.14.1
>>
>
>
>
>-- 
>Benjamin Gaignard
>
>Graphic Study Group
>
>Linaro.org │ Open source software for ARM SoCs
>
>Follow Linaro: Facebook | Twitter | Blog
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Benjamin Gaignard Oct. 3, 2017, 2:01 p.m. UTC | #3

2017-09-29 22:01 GMT+02:00 William Breathitt Gray <[e-mail]>:
> On Fri, Sep 29, 2017 at 03:42:02PM +0200, Benjamin Gaignard wrote:
>>2017-09-25 20:08 GMT+02:00 William Breathitt Gray <[e-mail]>:
>>> This patch introduces the IIO generic counter interface for supporting
>>> counter devices. The generic counter interface serves as a catch-all to
>>> enable rudimentary support for devices that qualify as counters. More
>>> specific and apt counter interfaces may be developed on top of the
>>> generic counter interface, and those interfaces should be used by
>>> drivers when possible rather than the generic counter interface.
>>>
>>> In the context of the IIO generic counter interface, a counter is
>>> defined as a device that reports one or more "counter values" based on
>>> the state changes of one or more "counter signals" as evaluated by a
>>> defined "counter function."
>>>
>>> The IIO generic counter interface piggybacks off of the IIO core. This
>>> is primarily used to leverage the existing sysfs setup: the IIO_COUNT
>>> channel attributes represent the "counter value," while the IIO_SIGNAL
>>> channel attributes represent the "counter signal;" auxilary IIO_COUNT
>>> attributes represent the "counter signal" connections and their
>>> respective state change configurations which trigger an associated
>>> "counter function" evaluation.
>>>
>>> The iio_counter_ops structure serves as a container for driver callbacks
>>> to communicate with the device; function callbacks are provided to read
>>> and write various "counter signals" and "counter values," and set and
>>> get the "trigger mode" and "function mode" for various "counter signals"
>>> and "counter values" respectively.
>>>
>>> To support a counter device, a driver must first allocate the available
>>> "counter signals" via iio_counter_signal structures. These "counter
>>> signals" should be stored as an array and set to the init_signals member
>>> of an allocated iio_counter structure before the counter is registered.
>>>
>>> "Counter values" may be allocated via iio_counter_value structures, and
>>> respective "counter signal" associations made via iio_counter_trigger
>>> structures. Initial associated iio_counter_trigger structures may be
>>> stored as an array and set to the the init_triggers member of the
>>> respective iio_counter_value structure. These iio_counter_value
>>> structures may be set to the init_values member of an allocated
>>> iio_counter structure before the counter is registered if so desired.
>>>
>>> A counter device is registered to the system by passing the respective
>>> initialized iio_counter structure to the iio_counter_register function;
>>> similarly, the iio_counter_unregister function unregisters the
>>> respective counter.
>>>
>>> Signed-off-by: William Breathitt Gray <[e-mail]>
>>
>>Hi William,
>>
>>Thanks for your patches, I start try to implement them in stm32-timer driver
>>but I think it will take me some time before understand all your code.
>>
>>I have some warning when compiling the code (see below).
>
> Hi Benjamin,
>
> Thank you for trying out the patches. I've been focusing on the main API
> documentation thus far, so unfortunately the current code is still a bit
> hard to follow -- hopefully I can clean it up some soon. Regardless,
> I'll be happy to answer any questions you may encounter while reviewing
> the patches.
>
> Regarding the compilation warnings: see my response inline below.
>
>>
>>About wording, I think that using "trigger" to describe signal active
>>states/edges
>>could be confusing in IIO context but I haven't found yet a better name.
>
> I agree very much with this. "Trigger" was a bad name choice when I
> developed the Generic Counter paradigm. I would like to come up with a
> better name for this component before this patchset is merged.
>
> The "Trigger" component essentially describes an association between a
> Signal and Value. The association typically has a defined Signal data
> condition which triggers the respective Value function operation (or
> occasionally the trigger condition is just left as "None"), but
> ultimately it's the association itself that is the key aspect this
> component.
>
> I have considered changing it to "Association" or "Connection" as the
> name, but both of these seem to sound too vague of terms. I shall keep
> thinking of various alternative names for this component and change the
> documentation in a subsequent patchset version once we have a more
> fitting name.

Yes it isn't easy to find the good name for that, maybe signal capabilities or
signal behavoir could also be considere.

>
>>
>>I also not very sure about what you expect from iio_counter_ops signal_read and
>>signal_write functions, do you think get/set the value of the signal ?
>>(i.e read gpio level ?)
>
> Yes, for an ordinary simple counter, signal_read and signal_write would
> typically expose control of the respective hardware input line level.
>
> However, it is important to remember that within the context of the
> Generic Counter paradigm, Signals are abstract components: a single
> Signal may not directly correlate to a single hardware input line; this
> is the primary reason for providing the signal_read/signal_write
> functions.
>
> For example, suppose we have a counter with a single Value associated to
> a single Signal. The Signal data is a 3-bit decimal value, and the Value
> is an ongoing count of the number of times the Signal data decimal value
> has had a value greater than "5."
>
> The hardware itself could consist of three individual input lines
> (one for each bit), but there is ultimately only one Signal. In this
> scenario, I would expect signal_read to simply return the 3-bit decimal
> value -- not the three physical hardware input line level. Notice the
> abstraction which has occurred: the Signal is the data represented by
> the hardware input, but not the raw hardware input itself.

I do not have access to the hardware input value anyway so I will just
keep those functions empty.

I have done some progress in driver implementation but I have questions
and suggestion, see below.

Benjamin

>
> Sincerely,
>
> William Breathitt Gray
>
>>
>>I will continue to review and implement your patches, I hope that end
>>of next week
>>have something functionnal to share with you.
>>
>>Thansk to have propose this, I do believe it will be helpful
>>
>>Benjamin
>>> ---
>>>  MAINTAINERS                        |    7 +
>>>  drivers/iio/Kconfig                |    8 +
>>>  drivers/iio/Makefile               |    1 +
>>>  drivers/iio/counter/Kconfig        |    1 +
>>>  drivers/iio/industrialio-counter.c | 1151 ++++++++++++++++++++++++++++++++++++
>>>  include/linux/iio/counter.h        |  221 +++++++
>>>  6 files changed, 1389 insertions(+)
>>>  create mode 100644 drivers/iio/industrialio-counter.c
>>>  create mode 100644 include/linux/iio/counter.h
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index 6f7721d1634c..24fc2dcf1995 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -6577,6 +6577,13 @@ F:       Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>>>  F:     Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
>>>  F:     drivers/iio/adc/envelope-detector.c
>>>
>>> +IIO GENERIC COUNTER INTERFACE
>>> +M:     William Breathitt Gray <[e-mail]>
>>> +L:     [e-mail]
>>> +S:     Maintained
>>> +F:     drivers/iio/industrialio-counter.c
>>> +F:     include/linux/iio/counter.h
>>> +
>>>  IIO MULTIPLEXER
>>>  M:     Peter Rosin <[e-mail]>
>>>  L:     [e-mail]
>>> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
>>> index b3c8c6ef0dff..78e01f4f5937 100644
>>> --- a/drivers/iio/Kconfig
>>> +++ b/drivers/iio/Kconfig
>>> @@ -30,6 +30,14 @@ config IIO_CONFIGFS
>>>           (e.g. software triggers). For more info see
>>>           Documentation/iio/iio_configfs.txt.
>>>
>>> +config IIO_COUNTER
>>> +       bool "Enable IIO counter support"
>>> +       help
>>> +         Provides IIO core support for counters. This API provides
>>> +         a generic interface that serves as the building blocks to
>>> +         create more complex counter interfaces. Rudimentary support
>>> +         for counters is enabled.
>>> +
>>>  config IIO_TRIGGER
>>>         bool "Enable triggered sampling support"
>>>         help
>>> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
>>> index 93c769cd99bf..6427ff38f964 100644
>>> --- a/drivers/iio/Makefile
>>> +++ b/drivers/iio/Makefile
>>> @@ -5,6 +5,7 @@
>>>  obj-$(CONFIG_IIO) += industrialio.o
>>>  industrialio-y := industrialio-core.o industrialio-event.o inkern.o
>>>  industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
>>> +industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
>>>  industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
>>>
>>>  obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
>>> diff --git a/drivers/iio/counter/Kconfig b/drivers/iio/counter/Kconfig
>>> index b37e5fc03149..3d46a790d8db 100644
>>> --- a/drivers/iio/counter/Kconfig
>>> +++ b/drivers/iio/counter/Kconfig
>>> @@ -4,6 +4,7 @@
>>>  # When adding new entries keep the list in alphabetical order
>>>
>>>  menu "Counters"
>>> +       depends on IIO_COUNTER
>>>
>>>  config 104_QUAD_8
>>>         tristate "ACCES 104-QUAD-8 driver"
>>> diff --git a/drivers/iio/industrialio-counter.c b/drivers/iio/industrialio-counter.c
>>> new file mode 100644
>>> index 000000000000..bdf190d010e4
>>> --- /dev/null
>>> +++ b/drivers/iio/industrialio-counter.c
>>> @@ -0,0 +1,1151 @@
>>> +/*
>>> + * Industrial I/O counter interface functions
>>> + * Copyright (C) 2017 William Breathitt Gray
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License, version 2, as
>>> + * published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope that it will be useful, but
>>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>> + * General Public License for more details.
>>> + */
>>> +#include <linux/err.h>
>>> +#include <linux/export.h>
>>> +#include <linux/gfp.h>
>>> +#include <linux/kernel.h>
>>> +#include <linux/list.h>
>>> +#include <linux/mutex.h>
>>> +#include <linux/printk.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/string.h>
>>> +
>>> +#include <linux/iio/iio.h>
>>> +#include <linux/iio/types.h>
>>> +
>>> +#include <linux/iio/counter.h>
>>> +
>>> +static struct iio_counter_signal *iio_counter_signal_find_by_id(
>>> +       const struct iio_counter *const counter, const int id)
>>> +{
>>> +       struct iio_counter_signal *iter;
>>> +
>>> +       list_for_each_entry(iter, &counter->signal_list, list)
>>> +               if (iter->id == id)
>>> +                       return iter;
>>> +
>>> +       return NULL;
>>> +}
>>> +
>>> +static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
>>> +       const struct iio_counter_value *const value, const int id)
>>> +{
>>> +       struct iio_counter_trigger *iter;
>>> +
>>> +       list_for_each_entry(iter, &value->trigger_list, list)
>>> +               if (iter->signal->id == id)
>>> +                       return iter;
>>> +
>>> +       return NULL;
>>> +}
>>> +
>>> +static struct iio_counter_value *iio_counter_value_find_by_id(
>>> +       const struct iio_counter *const counter, const int id)
>>> +{
>>> +       struct iio_counter_value *iter;
>>> +
>>> +       list_for_each_entry(iter, &counter->value_list, list)
>>> +               if (iter->id == id)
>>> +                       return iter;
>>> +
>>> +       return NULL;
>>> +}
>>> +
>>> +static void iio_counter_trigger_unregister_all(
>>> +       struct iio_counter_value *const value)
>>> +{
>>> +       struct iio_counter_trigger *iter, *tmp_iter;
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +       list_for_each_entry_safe(iter, tmp_iter, &value->trigger_list, list)
>>> +               list_del(&iter->list);
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +}
>>> +
>>> +static void iio_counter_signal_unregister_all(struct iio_counter *const counter)
>>> +{
>>> +       struct iio_counter_signal *iter, *tmp_iter;
>>> +
>>> +       mutex_lock(&counter->signal_list_lock);
>>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->signal_list, list)
>>> +               list_del(&iter->list);
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +}
>>> +
>>> +static void iio_counter_value_unregister_all(struct iio_counter *const counter)
>>> +{
>>> +       struct iio_counter_value *iter, *tmp_iter;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->value_list, list) {
>>> +               iio_counter_trigger_unregister_all(iter);
>>> +
>>> +               list_del(&iter->list);
>>> +       }
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +}
>>> +
>>> +static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       const struct iio_counter_signal *signal;
>>> +
>>> +       mutex_lock(&counter->signal_list_lock);
>>> +       signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +       if (!signal)
>>> +               return -EINVAL;
>>> +
>>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
>>> +}
>>> +
>>> +static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,
>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       const struct iio_counter_value *value;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +       if (!value)
>>> +               return -EINVAL;
>>> +
>>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", value->name);
>>> +}
>>> +
>>> +static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       const struct iio_counter_trigger *trigger;
>>> +       ssize_t len = 0;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               len = -EINVAL;
>>> +               goto err_find_value;
>>> +       }
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +       list_for_each_entry(trigger, &value->trigger_list, list) {
>>> +               len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
>>> +                       trigger->signal->id, trigger->signal->name,
>>> +                       trigger->trigger_modes[trigger->mode]);
>>> +               if (len >= PAGE_SIZE) {
>>> +                       len = -ENOMEM;
>>> +                       goto err_no_buffer_space;
>>> +               }
>>> +       }
>>> +err_no_buffer_space:
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +err_find_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return len;
>>> +}
>>> +
>>> +static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       ssize_t ret;
>>> +       struct iio_counter_trigger *trigger;
>>> +       const int signal_id = *(int *)((void *)priv);
>>> +       int mode;
>>> +
>>> +       if (!counter->ops->trigger_mode_get)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               ret = -EINVAL;
>>> +               goto err_value;
>>> +       }
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +
>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>> +       if (!trigger) {
>>> +               ret = -EINVAL;
>>> +               goto err_trigger;
>>> +       }
>>> +
>>> +       mode = counter->ops->trigger_mode_get(counter, value, trigger);
>>> +
>>> +       if (mode < 0) {
>>> +               ret = mode;
>>> +               goto err_trigger;
>>> +       } else if (mode >= trigger->num_trigger_modes) {
>>> +               ret = -EINVAL;
>>> +               goto err_trigger;
>>> +       }
>>> +
>>> +       trigger->mode = mode;
>>> +
>>> +       ret = scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
>>> +
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return ret;
>>> +
>>> +err_trigger:
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +err_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +       return ret;
>>> +}
>>> +
>>> +static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
>>> +       uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
>>> +       size_t len)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       ssize_t err;
>>> +       struct iio_counter_trigger *trigger;
>>> +       const int signal_id = *(int *)((void *)priv);
>>> +       unsigned int mode;
>>> +
>>> +       if (!counter->ops->trigger_mode_set)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               err = -EINVAL;
>>> +               goto err_value;
>>> +       }
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +
>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>> +       if (!trigger) {
>>> +               err = -EINVAL;
>>> +               goto err_trigger;
>>> +       }
>>> +
>>> +       for (mode = 0; mode < trigger->num_trigger_modes; mode++)
>>> +               if (sysfs_streq(buf, trigger->trigger_modes[mode]))
>>> +                       break;
>>> +
>>> +       if (mode >= trigger->num_trigger_modes) {
>>> +               err = -EINVAL;
>>> +               goto err_trigger;
>>> +       }
>>> +
>>> +       err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
>>> +       if (err)
>>> +               goto err_trigger;
>>> +
>>> +       trigger->mode = mode;
>>> +
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return len;
>>> +
>>> +err_trigger:
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +err_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +       return err;
>>> +}
>>> +
>>> +static ssize_t iio_counter_trigger_mode_available_read(
>>> +       struct iio_dev *indio_dev, uintptr_t priv,
>>> +       const struct iio_chan_spec *chan, char *buf)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       ssize_t len = 0;
>>> +       struct iio_counter_trigger *trigger;
>>> +       const int signal_id = *(int *)((void *)priv);
>>> +       unsigned int i;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               len = -EINVAL;
>>> +               goto err_no_value;
>>> +       }
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +
>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>> +       if (!trigger) {
>>> +               len = -EINVAL;
>>> +               goto err_no_trigger;
>>> +       }
>>> +
>>> +       for (i = 0; i < trigger->num_trigger_modes; i++)
>>> +               len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
>>> +                       trigger->trigger_modes[i]);
>>> +
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       buf[len - 1] = '\n';
>>> +
>>> +       return len;
>>> +
>>> +err_no_trigger:
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +err_no_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +       return len;
>>> +}
>>> +
>>> +static int iio_counter_value_function_set(struct iio_dev *indio_dev,
>>> +       const struct iio_chan_spec *chan, unsigned int mode)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       int err;
>>> +
>>> +       if (!counter->ops->value_function_set)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               err = -EINVAL;
>>> +               goto err_value;
>>> +       }
>>> +
>>> +       err = counter->ops->value_function_set(counter, value, mode);
>>> +       if (err)
>>> +               goto err_value;
>>> +
>>> +       value->mode = mode;
>>> +
>>> +err_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return err;
>>> +}
>>> +
>>> +static int iio_counter_value_function_get(struct iio_dev *indio_dev,
>>> +       const struct iio_chan_spec *chan)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_value *value;
>>> +       int retval;
>>> +
>>> +       if (!counter->ops->value_function_get)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +       if (!value) {
>>> +               retval = -EINVAL;
>>> +               goto err_value;
>>> +       }
>>> +
>>> +       retval = counter->ops->value_function_get(counter, value);
>>> +       if (retval < 0)
>>> +               goto err_value;
>>> +       else if (retval >= value->num_function_modes) {
>>> +               retval = -EINVAL;
>>> +               goto err_value;
>>> +       }
>>> +
>>> +       value->mode = retval;
>>> +
>>> +err_value:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return retval;
>>> +}
>>> +
>>> +static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
>>> +       struct iio_counter_value *const value)
>>> +{
>>> +       const struct iio_chan_spec_ext_info ext_info_default[] = {
>>> +               {
>>> +                       .name = "name",
>>> +                       .shared = IIO_SEPARATE,
>>> +                       .read = iio_counter_value_name_read
>>> +               },
>>> +               IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
>>> +               {
>>> +                       .name = "function_available",
>>> +                       .shared = IIO_SEPARATE,
>>> +                       .read = iio_enum_available_read,
>>> +                       .private = (void *)&value->function_enum
>>I have this warning the 3 times that  private field is set
>>drivers/iio/industrialio-counter.c:401:15: warning: initialization
>>makes integer from pointer without a cast [-Wint-conversion]
>>    .private = (void *)&value->function_enum
>>
>>I think you can change it to "void *" instead of a uintptr_t
>
> These are pretty benign warnings which you may ignore: I'm doing an
> implicit conversion to uintptr_t which is ultimately an integer type; in
> general, pointer to integer conversations are unsafe, but there is a
> special exception in the C language for the uintptr_t data type. I could
> have used an explicit cast to avoid the warning but opted to leave it
> implicit to keep the code easier to read.
>
> However, it would be nice if the private member was void *, since the
> intent of my code would be clearer in that case (passing a pointer for
> later dereference). Unfortunately, I'm hesitant to submit a patch to
> change the "private" member data type to void * since other drivers may
> require the uintptr_t data type -- my suspicion is that there are some
> drivers out there which do since the choice to introduce the "private"
> member as a uintptr_t appears deliberate.
>
>>> +               },
>>> +               {
>>> +                       .name = "triggers",
>>> +                       .shared = IIO_SEPARATE,
>>> +                       .read = iio_counter_value_triggers_read
>>> +               }
>>> +       };
>>> +       const size_t num_default = ARRAY_SIZE(ext_info_default);
>>> +       const struct iio_chan_spec_ext_info ext_info_trigger[] = {
>>> +               {
>>> +                       .shared = IIO_SEPARATE,
>>> +                       .read = iio_counter_trigger_mode_read,
>>> +                       .write = iio_counter_trigger_mode_write
>>> +               },
>>> +               {
>>> +                       .shared = IIO_SEPARATE,
>>> +                       .read = iio_counter_trigger_mode_available_read
>>> +               }
>>> +       };
>>> +       const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
>>> +       const struct list_head *pos;
>>> +       size_t num_triggers = 0;
>>> +       size_t num_triggers_ext_info;
>>> +       size_t num_ext_info;
>>> +       int err;
>>> +       struct iio_chan_spec_ext_info *ext_info;
>>> +       const struct iio_counter_trigger *trigger_pos;
>>> +       size_t i;
>>> +
>>> +       value->function_enum.items = value->function_modes;
>>> +       value->function_enum.num_items = value->num_function_modes;
>>> +       value->function_enum.set = iio_counter_value_function_set;
>>> +       value->function_enum.get = iio_counter_value_function_get;
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +
>>> +       list_for_each(pos, &value->trigger_list)
>>> +               num_triggers++;
>>> +
>>> +       num_triggers_ext_info = num_ext_info_trigger * num_triggers;
>>> +       num_ext_info = num_default + num_triggers_ext_info + 1;
>>> +
>>> +       ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
>>> +       if (!ext_info) {
>>> +               err = -ENOMEM;
>>> +               goto err_ext_info_alloc;
>>> +       }
>>> +       ext_info[num_ext_info - 1].name = NULL;
>>> +
>>> +       memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
>>> +       for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
>>> +               memcpy(ext_info + num_default + i, ext_info_trigger,
>>> +                       sizeof(ext_info_trigger));
>>> +
>>> +       i = num_default;
>>> +       list_for_each_entry(trigger_pos, &value->trigger_list, list) {
>>> +               ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
>>> +                       chan->channel, trigger_pos->signal->id);
>>> +               if (!ext_info[i].name) {
>>> +                       err = -ENOMEM;
>>> +                       goto err_name_alloc;
>>> +               }
>>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>>> +               i++;
>>> +
>>> +               ext_info[i].name = kasprintf(GFP_KERNEL,
>>> +                       "trigger_signal%d-%d_available",
>>> +                       chan->channel, trigger_pos->signal->id);
>>> +               if (!ext_info[i].name) {
>>> +                       err = -ENOMEM;
>>> +                       goto err_name_alloc;
>>> +               }
>>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>>> +               i++;
>>> +       }
>>> +
>>> +       chan->ext_info = ext_info;
>>> +
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +       return 0;
>>> +
>>> +err_name_alloc:
>>> +       while (i-- > num_default)
>>> +               kfree(ext_info[i].name);
>>> +       kfree(ext_info);
>>> +err_ext_info_alloc:
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +       return err;
>>> +}
>>> +
>>> +static void iio_counter_value_ext_info_free(
>>> +       const struct iio_chan_spec *const channel)
>>> +{
>>> +       size_t i;
>>> +       const char *const prefix = "trigger_signal";
>>> +       const size_t prefix_len = strlen(prefix);
>>> +
>>> +       for (i = 0; channel->ext_info[i].name; i++)
>>> +               if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
>>> +                       kfree(channel->ext_info[i].name);
>>> +       kfree(channel->ext_info);
>>> +}
>>> +
>>> +static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
>>> +       {
>>> +               .name = "name",
>>> +               .shared = IIO_SEPARATE,
>>> +               .read = iio_counter_signal_name_read
>>> +       },
>>> +       {}
>>> +};
>>> +
>>> +static int iio_counter_channels_alloc(struct iio_counter *const counter)
>>> +{
>>> +       const struct list_head *pos;
>>> +       size_t num_channels = 0;
>>> +       int err;
>>> +       struct iio_chan_spec *channels;
>>> +       struct iio_counter_value *value_pos;
>>> +       size_t i = counter->num_channels;
>>> +       const struct iio_counter_signal *signal_pos;
>>> +
>>> +       mutex_lock(&counter->signal_list_lock);
>>> +
>>> +       list_for_each(pos, &counter->signal_list)
>>> +               num_channels++;
>>> +
>>> +       if (!num_channels) {
>>> +               err = -EINVAL;
>>> +               goto err_no_signals;
>>> +       }
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +
>>> +       list_for_each(pos, &counter->value_list)
>>> +               num_channels++;
>>> +
>>> +       num_channels += counter->num_channels;
>>> +
>>> +       channels = kcalloc(num_channels, sizeof(*channels), GFP_KERNEL);
>>> +       if (!channels) {
>>> +               err = -ENOMEM;
>>> +               goto err_channels_alloc;
>>> +       }
>>> +
>>> +       memcpy(channels, counter->channels,
>>> +               counter->num_channels * sizeof(*counter->channels));
>>> +
>>> +       list_for_each_entry(value_pos, &counter->value_list, list) {
>>> +               channels[i].type = IIO_COUNT;
>>> +               channels[i].channel = counter->id;
>>> +               channels[i].channel2 = value_pos->id;
>>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>>> +               channels[i].indexed = 1;
>>> +               channels[i].counter = 1;
>>> +
>>> +               err = iio_counter_value_ext_info_alloc(channels + i, value_pos);
>>> +               if (err)
>>> +                       goto err_value_ext_info_alloc;
>>> +
>>> +               i++;
>>> +       }
>>> +
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       list_for_each_entry(signal_pos, &counter->signal_list, list) {
>>> +               channels[i].type = IIO_SIGNAL;
>>> +               channels[i].channel = counter->id;
>>> +               channels[i].channel2 = signal_pos->id;
>>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>>> +               channels[i].indexed = 1;
>>> +               channels[i].counter = 1;
>>> +               channels[i].ext_info = iio_counter_signal_ext_info;
>>> +
>>> +               i++;
>>> +       }
>>> +
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +
>>> +       counter->indio_dev->num_channels = num_channels;
>>> +       counter->indio_dev->channels = channels;
>>> +
>>> +       return 0;
>>> +
>>> +err_value_ext_info_alloc:
>>> +       while (i-- > counter->num_channels)
>>> +               iio_counter_value_ext_info_free(channels + i);
>>> +       kfree(channels);
>>> +err_channels_alloc:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +err_no_signals:
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +       return err;
>>> +}
>>> +
>>> +static void iio_counter_channels_free(const struct iio_counter *const counter)
>>> +{
>>> +       size_t i = counter->num_channels + counter->indio_dev->num_channels;
>>> +       const struct iio_chan_spec *const chans = counter->indio_dev->channels;
>>> +
>>> +       while (i-- > counter->num_channels)
>>> +               if (chans[i].type == IIO_COUNT)
>>> +                       iio_counter_value_ext_info_free(chans + i);
>>> +
>>> +       kfree(chans);
>>> +}
>>> +
>>> +static int iio_counter_read_raw(struct iio_dev *indio_dev,
>>> +       struct iio_chan_spec const *chan, int *val, int *val2, long mask)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_signal *signal;
>>> +       int retval;
>>> +       struct iio_counter_value *value;
>>> +
>>> +       if (mask != IIO_CHAN_INFO_RAW)
>>> +               return -EINVAL;
>>> +
>>> +       switch (chan->type) {
>>> +       case IIO_SIGNAL:
>>> +               if (!counter->ops->signal_read)
>>> +                       return -EINVAL;
>>> +
>>> +               mutex_lock(&counter->signal_list_lock);
>>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>> +               if (!signal) {
>>> +                       mutex_unlock(&counter->signal_list_lock);
>>> +                       return -EINVAL;
>>> +               }
>>> +
>>> +               retval = counter->ops->signal_read(counter, signal, val, val2);
>>> +               mutex_unlock(&counter->signal_list_lock);
>>> +
>>> +               return retval;
>>> +       case IIO_COUNT:
>>> +               if (!counter->ops->value_read)
>>> +                       return -EINVAL;
>>> +
>>> +               mutex_lock(&counter->value_list_lock);
>>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +               if (!value) {
>>> +                       mutex_unlock(&counter->value_list_lock);
>>> +                       return -EINVAL;
>>> +               }
>>> +
>>> +               retval = counter->ops->value_read(counter, value, val, val2);
>>> +               mutex_unlock(&counter->value_list_lock);
>>> +
>>> +               return retval;
>>> +       default:
>>> +               if (counter->info && counter->info->read_raw)
>>> +                       return counter->info->read_raw(indio_dev, chan, val,
>>> +                               val2, mask);
>>> +       }
>>> +
>>> +       return -EINVAL;
>>> +}
>>> +
>>> +static int iio_counter_write_raw(struct iio_dev *indio_dev,
>>> +       struct iio_chan_spec const *chan, int val, int val2, long mask)
>>> +{
>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>> +       struct iio_counter_signal *signal;
>>> +       int retval;
>>> +       struct iio_counter_value *value;
>>> +
>>> +       if (mask != IIO_CHAN_INFO_RAW)
>>> +               return -EINVAL;

I have an issue with this check because I believe it make impossible to call
the callback registered in iio_info since the channel isn't always
IIO_CHAN_INFO_RAW
but could be  IIO_CHAN_INFO_ENABLE or IIO_CHAN_INFO_SCALE in my driver.
Maybe it is comming from my code be I don't understand how it could
works in 104-quad-8 either

>>> +
>>> +       switch (chan->type) {
>>> +       case IIO_SIGNAL:
>>> +               if (!counter->ops->signal_write)
>>> +                       return -EINVAL;
>>> +
>>> +               mutex_lock(&counter->signal_list_lock);
>>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>> +               if (!signal) {
>>> +                       mutex_unlock(&counter->signal_list_lock);
>>> +                       return -EINVAL;
>>> +               }
>>> +
>>> +               retval = counter->ops->signal_write(counter, signal, val, val2);
>>> +               mutex_unlock(&counter->signal_list_lock);
>>> +
>>> +               return retval;
>>> +       case IIO_COUNT:
>>> +               if (!counter->ops->value_write)
>>> +                       return -EINVAL;
>>> +
>>> +               mutex_lock(&counter->value_list_lock);
>>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>>> +               if (!value) {
>>> +                       mutex_unlock(&counter->value_list_lock);
>>> +                       return -EINVAL;
>>> +               }
>>> +
>>> +               retval = counter->ops->value_write(counter, value, val, val2);
>>> +               mutex_unlock(&counter->value_list_lock);
>>> +
>>> +               return retval;
>>> +       default:
>>> +               if (counter->info && counter->info->write_raw)
>>> +                       return counter->info->write_raw(indio_dev, chan, val,
>>> +                               val2, mask);
>>> +       }
>>> +
>>> +       return -EINVAL;
>>> +}
>>> +
>>> +static int iio_counter_signal_register(struct iio_counter *const counter,
>>> +       struct iio_counter_signal *const signal)
>>> +{
>>> +       int err;
>>> +
>>> +       if (!counter || !signal)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&counter->signal_list_lock);
>>> +       if (iio_counter_signal_find_by_id(counter, signal->id)) {
>>> +               pr_err("Duplicate counter signal ID '%d'\n", signal->id);
>>> +               err = -EEXIST;
>>> +               goto err_duplicate_id;
>>> +       }
>>> +       list_add_tail(&signal->list, &counter->signal_list);
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +
>>> +       return 0;
>>> +
>>> +err_duplicate_id:
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +       return err;
>>> +}
>>> +
>>> +static void iio_counter_signal_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_signal *const signal)
>>> +{
>>> +       if (!counter || !signal)
>>> +               return;
>>> +
>>> +       mutex_lock(&counter->signal_list_lock);
>>> +       list_del(&signal->list);
>>> +       mutex_unlock(&counter->signal_list_lock);
>>> +}
>>> +
>>> +static int iio_counter_signals_register(struct iio_counter *const counter,
>>> +       struct iio_counter_signal *const signals, const size_t num_signals)
>>> +{
>>> +       size_t i;
>>> +       int err;
>>> +
>>> +       if (!counter || !signals)
>>> +               return -EINVAL;
>>> +
>>> +       for (i = 0; i < num_signals; i++) {
>>> +               err = iio_counter_signal_register(counter, signals + i);
>>> +               if (err)
>>> +                       goto err_signal_register;
>>> +       }
>>> +
>>> +       return 0;
>>> +
>>> +err_signal_register:
>>> +       while (i--)
>>> +               iio_counter_signal_unregister(counter, signals + i);
>>> +       return err;
>>> +}
>>> +
>>> +static void iio_counter_signals_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_signal *signals, size_t num_signals)
>>> +{
>>> +       if (!counter || !signals)
>>> +               return;
>>> +
>>> +       while (num_signals--) {
>>> +               iio_counter_signal_unregister(counter, signals);
>>> +               signals++;
>>> +       }
>>> +}
>>> +
>>> +/**
>>> + * iio_counter_trigger_register - register Trigger to Value
>>> + * @value: pointer to IIO Counter Value for association
>>> + * @trigger: pointer to IIO Counter Trigger to register
>>> + *
>>> + * The Trigger is added to the Value's trigger_list. A check is first performed
>>> + * to verify that the respective Signal is not already linked to the Value; if
>>> + * the respective Signal is already linked to the Value, the Trigger is not
>>> + * added to the Value's trigger_list.
>>> + *
>>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>>> + * during execution.
>>> + */
>>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const trigger)
>>> +{
>>> +       if (!value || !trigger || !trigger->signal)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +       if (iio_counter_trigger_find_by_id(value, trigger->signal->id)) {
>>> +               pr_err("Signal%d is already linked to counter value%d\n",
>>> +                       trigger->signal->id, value->id);
>>> +               return -EEXIST;
>>> +       }
>>> +       list_add_tail(&trigger->list, &value->trigger_list);
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +
>>> +       return 0;
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_trigger_register);
>>> +
>>> +/**
>>> + * iio_counter_trigger_unregister - unregister Trigger from Value
>>> + * @value: pointer to IIO Counter Value of association
>>> + * @trigger: pointer to IIO Counter Trigger to unregister
>>> + *
>>> + * The Trigger is removed from the Value's trigger_list.
>>> + *
>>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>>> + * during execution.
>>> + */
>>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const trigger)
>>> +{
>>> +       if (!value || !trigger || !trigger->signal)
>>> +               return;
>>> +
>>> +       mutex_lock(&value->trigger_list_lock);
>>> +       list_del(&trigger->list);
>>> +       mutex_unlock(&value->trigger_list_lock);
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_trigger_unregister);
>>> +
>>> +/**
>>> + * iio_counter_triggers_register - register an array of Triggers to Value
>>> + * @value: pointer to IIO Counter Value for association
>>> + * @triggers: array of pointers to IIO Counter Triggers to register
>>> + *
>>> + * The iio_counter_trigger_register function is called for each Trigger in the
>>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>>> + *
>>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>>> + */
>>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers)
>>> +{
>>> +       size_t i;
>>> +       int err;
>>> +
>>> +       if (!value || !triggers)
>>> +               return -EINVAL;
>>> +
>>> +       for (i = 0; i < num_triggers; i++) {
>>> +               err = iio_counter_trigger_register(value, triggers + i);
>>> +               if (err)
>>> +                       goto err_trigger_register;
>>> +       }
>>> +
>>> +       return 0;
>>> +
>>> +err_trigger_register:
>>> +       while (i--)
>>> +               iio_counter_trigger_unregister(value, triggers + i);
>>> +       return err;
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_triggers_register);
>>> +
>>> +/**
>>> + * iio_counter_triggers_unregister - unregister Triggers from Value
>>> + * @value: pointer to IIO Counter Value of association
>>> + * @triggers: array of pointers to IIO Counter Triggers to unregister
>>> + *
>>> + * The iio_counter_trigger_unregister function is called for each Trigger in the
>>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>>> + *
>>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>>> + */
>>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *triggers, size_t num_triggers)
>>> +{
>>> +       if (!value || !triggers)
>>> +               return;
>>> +
>>> +       while (num_triggers--) {
>>> +               iio_counter_trigger_unregister(value, triggers);
>>> +               triggers++;
>>> +       }
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_triggers_unregister);
>>> +
>>> +/**
>>> + * iio_counter_value_register - register Value to Counter
>>> + * @counter: pointer to IIO Counter for association
>>> + * @value: pointer to IIO Counter Value to register
>>> + *
>>> + * The registration process occurs in two major steps. First, the Value is
>>> + * initialized: trigger_list_lock is initialized, trigger_list is initialized,
>>> + * and init_triggers if not NULL is passed to iio_counter_triggers_register.
>>> + * Second, the Value is added to the Counter's value_list. A check is first
>>> + * performed to verify that the Value is not already associated to the Counter
>>> + * (via the Value's unique ID); if the Value is already associated to the
>>> + * Counter, the Value is not added to the Counter's value_list and all of the
>>> + * Value's Triggers are unregistered.
>>> + *
>>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>>> + * during execution.
>>> + */
>>> +int iio_counter_value_register(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const value)
>>> +{
>>> +       int err;
>>> +
>>> +       if (!counter || !value)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_init(&value->trigger_list_lock);
>>> +       INIT_LIST_HEAD(&value->trigger_list);
>>> +
>>> +       if (value->init_triggers) {
>>> +               err = iio_counter_triggers_register(value,
>>> +                       value->init_triggers, value->num_init_triggers);
>>> +               if (err)
>>> +                       return err;
>>> +       }
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +       if (iio_counter_value_find_by_id(counter, value->id)) {
>>> +               pr_err("Duplicate counter value ID '%d'\n", value->id);
>>> +               err = -EEXIST;
>>> +               goto err_duplicate_id;
>>> +       }
>>> +       list_add_tail(&value->list, &counter->value_list);
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       return 0;
>>> +
>>> +err_duplicate_id:
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +       iio_counter_trigger_unregister_all(value);
>>> +       return err;
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_value_register);
>>> +
>>> +/**
>>> + * iio_counter_value_unregister - unregister Value from Counter
>>> + * @counter: pointer to IIO Counter of association
>>> + * @value: pointer to IIO Counter Value to unregister
>>> + *
>>> + * The Value is removed from the Counter's value_list and all of the Value's
>>> + * Triggers are unregistered.
>>> + *
>>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>>> + * during execution.
>>> + */
>>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const value)
>>> +{
>>> +       if (!counter || !value)
>>> +               return;
>>> +
>>> +       mutex_lock(&counter->value_list_lock);
>>> +       list_del(&value->list);
>>> +       mutex_unlock(&counter->value_list_lock);
>>> +
>>> +       iio_counter_trigger_unregister_all(value);
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_value_unregister);
>>> +
>>> +/**
>>> + * iio_counter_values_register - register an array of Values to Counter
>>> + * @counter: pointer to IIO Counter for association
>>> + * @values: array of pointers to IIO Counter Values to register
>>> + *
>>> + * The iio_counter_value_register function is called for each Value in the
>>> + * array. The @values array is traversed for the first @num_values Values.
>>> + *
>>> + * NOTE: @num_values must not be greater than the size of the @values array.
>>> + */
>>> +int iio_counter_values_register(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const values, const size_t num_values)
>>> +{
>>> +       size_t i;
>>> +       int err;
>>> +
>>> +       if (!counter || !values)
>>> +               return -EINVAL;
>>> +
>>> +       for (i = 0; i < num_values; i++) {
>>> +               err = iio_counter_value_register(counter, values + i);
>>> +               if (err)
>>> +                       goto err_values_register;
>>> +       }
>>> +
>>> +       return 0;
>>> +
>>> +err_values_register:
>>> +       while (i--)
>>> +               iio_counter_value_unregister(counter, values + i);
>>> +       return err;
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_values_register);
>>> +
>>> +/**
>>> + * iio_counter_values_unregister - unregister Values from Counter
>>> + * @counter: pointer to IIO Counter of association
>>> + * @values: array of pointers to IIO Counter Values to unregister
>>> + *
>>> + * The iio_counter_value_unregister function is called for each Value in the
>>> + * array. The @values array is traversed for the first @num_values Values.
>>> + *
>>> + * NOTE: @num_values must not be greater than the size of the @values array.
>>> + */
>>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_value *values, size_t num_values)
>>> +{
>>> +       if (!counter || !values)
>>> +               return;
>>> +
>>> +       while (num_values--) {
>>> +               iio_counter_value_unregister(counter, values);
>>> +               values++;
>>> +       }
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_values_unregister);
>>> +
>>> +/**
>>> + * iio_counter_register - register Counter to the system
>>> + * @counter: pointer to IIO Counter to register
>>> + *
>>> + * This function piggybacks off of iio_device_register. First, the relevant
>>> + * Counter members are initialized; if init_signals is not NULL it is passed to
>>> + * iio_counter_signals_register, and similarly if init_values is not NULL it is
>>> + * passed to iio_counter_values_register. Next, a struct iio_dev is allocated by
>>> + * a call to iio_device_alloc and initialized for the Counter, IIO channels are
>>> + * allocated, the Counter is copied as the private data, and finally
>>> + * iio_device_register is called.
>>> + */
>>> +int iio_counter_register(struct iio_counter *const counter)
>>> +{
>>> +       const struct iio_info info_default = {
>>> +               .read_raw = iio_counter_read_raw,
>>> +               .write_raw = iio_counter_write_raw
>>> +       };
>>> +       int err;
>>> +       struct iio_info *info;
>>> +       struct iio_counter *priv;
>>> +
>>> +       if (!counter)
>>> +               return -EINVAL;
>>> +
>>> +       mutex_init(&counter->signal_list_lock);
>>> +       INIT_LIST_HEAD(&counter->signal_list);
>>> +
>>> +       if (counter->init_signals) {
>>> +               err = iio_counter_signals_register(counter,
>>> +                       counter->init_signals, counter->num_init_signals);
>>> +               if (err)
>>> +                       return err;
>>> +       }
>>> +
>>> +       mutex_init(&counter->value_list_lock);
>>> +       INIT_LIST_HEAD(&counter->value_list);
>>> +
>>> +       if (counter->init_values) {
>>> +               err = iio_counter_values_register(counter,
>>> +                       counter->init_values, counter->num_init_values);
>>> +               if (err)
>>> +                       goto err_values_register;
>>> +       }
>>> +
>>> +       counter->indio_dev = iio_device_alloc(sizeof(*counter));
>>> +       if (!counter->indio_dev) {
>>> +               err = -ENOMEM;
>>> +               goto err_iio_device_alloc;
>>> +       }
>>> +
>>> +       info = kmalloc(sizeof(*info), GFP_KERNEL);
>>> +       if (!info) {
>>> +               err = -ENOMEM;
>>> +               goto err_info_alloc;
>>> +       }
>>> +       if (counter->info) {
>>> +               memcpy(info, counter->info, sizeof(*counter->info));
>>> +               info->read_raw = iio_counter_read_raw;
>>> +               info->write_raw = iio_counter_write_raw;
>>> +       } else {
>>> +               memcpy(info, &info_default, sizeof(info_default));
>>> +       }
>>> +
>>> +       counter->indio_dev->info = info;
>>> +       counter->indio_dev->modes = INDIO_DIRECT_MODE;

For stm32 triggerd river I need to be able to change indio_dev->modes
to INDIO_HARDWARE_TRIGGERED
Could you add a parameter to be able to configure teh modes ?

>>> +       counter->indio_dev->name = counter->name;
>>> +       counter->indio_dev->dev.parent = counter->dev;
>>> +
>>> +       err = iio_counter_channels_alloc(counter);
>>> +       if (err)
>>> +               goto err_channels_alloc;
>>> +
>>> +       priv = iio_priv(counter->indio_dev);
>>> +       memcpy(priv, counter, sizeof(*priv));
>>> +
>>> +       err = iio_device_register(priv->indio_dev);
>>> +       if (err)
>>> +               goto err_iio_device_register;
>>> +
>>> +       return 0;
>>> +
>>> +err_iio_device_register:
>>> +       iio_counter_channels_free(counter);
>>> +err_channels_alloc:
>>> +       kfree(info);
>>> +err_info_alloc:
>>> +       iio_device_free(counter->indio_dev);
>>> +err_iio_device_alloc:
>>> +       iio_counter_values_unregister(counter, counter->init_values,
>>> +               counter->num_init_values);
>>> +err_values_register:
>>> +       iio_counter_signals_unregister(counter, counter->init_signals,
>>> +               counter->num_init_signals);
>>> +       return err;
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_register);
>>> +
>>> +/**
>>> + * iio_counter_unregister - unregister Counter from the system
>>> + * @counter: pointer to IIO Counter to unregister
>>> + *
>>> + * The Counter is unregistered from the system. The indio_dev is unregistered,
>>> + * allocated memory is freed, and all associated Values and Signals are
>>> + * unregistered.
>>> + */
>>> +void iio_counter_unregister(struct iio_counter *const counter)
>>> +{
>>> +       const struct iio_info *const info = counter->indio_dev->info;
>>> +
>>> +       if (!counter)
>>> +               return;
>>> +
>>> +       iio_device_unregister(counter->indio_dev);
>>> +
>>> +       iio_counter_channels_free(counter);
>>> +
>>> +       kfree(info);
>>> +       iio_device_free(counter->indio_dev);
>>> +
>>> +       iio_counter_value_unregister_all(counter);
>>> +       iio_counter_signal_unregister_all(counter);
>>> +}
>>> +EXPORT_SYMBOL(iio_counter_unregister);

I have added devm_iio_counter_register and devm_iio_counter_unregister to avoid
add remove in driver code. If that make sense for you can add tehm in your code
/**
 * devm_iio_counter_register - Resource-managed iio_counter_register()
 * @dev: Device to allocate iio_dev for
 * @counter: pointer to IIO Counter to register
 *
 * Managed iio_counter_register.  The IIO counter registered with this
 * function is automatically unregistered on driver detach. This function
 * calls iio_counter_register() internally. Refer to that function for more
 * information.
 *
 * If an iio counter registered with this function needs to be unregistered
 * separately, devm_iio_counter_unregister() must be used.
 *
 * RETURNS:
 * 0 on success, negative error number on failure.
 */
int devm_iio_counter_register(struct device *dev,
      struct iio_counter *const counter)
{
struct iio_counter **ptr;
int ret;

ptr = devres_alloc(devm_iio_counter_unreg, sizeof(*ptr), GFP_KERNEL);
if (!ptr)
return -ENOMEM;

*ptr = counter;
ret = iio_counter_register(counter);
if (!ret)
devres_add(dev, ptr);
else
devres_free(ptr);

return ret;

}
EXPORT_SYMBOL(devm_iio_counter_register);

static int devm_iio_counter_match(struct device *dev, void *res, void *data)
{
struct iio_counter **r = res;
if (!r || !*r) {
WARN_ON(!r || !*r);
return 0;
}
return *r == data;
}

/**
 * devm_iio_counter_unregister - Resource-managed iio_counter_unregister()
 * @dev: Device this iio_dev belongs to
 * @counter: the iio counter associated with the device
 *
 * Unregister iio counter registered with devm_iio_counter_register().
 */
void devm_iio_counter_unregister(struct device *dev,
struct iio_counter *const counter)
{
int rc;

rc = devres_release(dev, devm_iio_counter_unreg,
    devm_iio_counter_match, counter);
WARN_ON(rc);
}
EXPORT_SYMBOL(devm_iio_counter_unregister);

>>> diff --git a/include/linux/iio/counter.h b/include/linux/iio/counter.h
>>> new file mode 100644
>>> index 000000000000..1c1ca13a6053
>>> --- /dev/null
>>> +++ b/include/linux/iio/counter.h
>>> @@ -0,0 +1,221 @@
>>> +/*
>>> + * Industrial I/O counter interface
>>> + * Copyright (C) 2017 William Breathitt Gray
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License, version 2, as
>>> + * published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope that it will be useful, but
>>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>> + * General Public License for more details.
>>> + */
>>> +#ifndef _IIO_COUNTER_H_
>>> +#define _IIO_COUNTER_H_
>>> +
>>> +#ifdef CONFIG_IIO_COUNTER
>>> +
>>> +#include <linux/device.h>
>>> +#include <linux/mutex.h>
>>> +#include <linux/types.h>
>>> +
>>> +#include <linux/iio/iio.h>
>>> +
>>> +/**
>>> + * struct iio_counter_signal - IIO Counter Signal node
>>> + * @id:                [DRIVER] unique ID used to identify signal
>>> + * @name:      [DRIVER] device-specific signal name
>>> + * @list:      [INTERN] list of all signals currently registered to counter
>>> + */
>>> +struct iio_counter_signal {
>>> +       int             id;
>>> +       const char      *name;
>>> +
>>> +       struct list_head        list;
>>> +};
>>> +
>>> +/**
>>> + * struct iio_counter_trigger - IIO Counter Trigger node
>>> + * @mode:              [DRIVER] current trigger mode state
>>> + * @trigger_modes:     [DRIVER] available trigger modes
>>> + * @num_trigger_modes: [DRIVER] number of modes specified in @trigger_modes
>>> + * @signal:            [DRIVER] pointer to associated signal
>>> + * @list:              [INTERN] list of all triggers currently registered to
>>> + *                     value
>>> + */
>>> +struct iio_counter_trigger {
>>> +       unsigned int                    mode;
>>> +       const char *const               *trigger_modes;
>>> +       unsigned int                    num_trigger_modes;
>>> +       struct iio_counter_signal       *signal;
>>> +
>>> +       struct list_head                list;
>>> +};
>>> +
>>> +/**
>>> + * struct iio_counter_value - IIO Counter Value node
>>> + * @id:                        [DRIVER] unique ID used to identify value
>>> + * @name:              [DRIVER] device-specific value name
>>> + * @mode:              [DRIVER] current function mode state
>>> + * @function_modes:    [DRIVER] available function modes
>>> + * @num_function_modes:        [DRIVER] number of modes specified in @function_modes
>>> + * @init_triggers:     [DRIVER] array of triggers for initialization
>>> + * @num_init_triggers: [DRIVER] number of triggers specified in @init_triggers
>>> + * @function_enum:     [INTERN] used internally to generate function attributes
>>> + * @trigger_list_lock: [INTERN] lock for accessing @trigger_list
>>> + * @trigger_list:      [INTERN] list of all triggers currently registered to
>>> + *                     value
>>> + * @list:              [INTERN] list of all values currently registered to
>>> + *                     counter
>>> + */
>>> +struct iio_counter_value {
>>> +       int                     id;
>>> +       const char              *name;
>>> +       unsigned int            mode;
>>> +       const char *const       *function_modes;
>>> +       unsigned int            num_function_modes;
>>> +
>>> +       struct iio_counter_trigger      *init_triggers;
>>> +       size_t                          num_init_triggers;
>>> +
>>> +       struct iio_enum         function_enum;
>>> +       struct mutex            trigger_list_lock;
>>> +       struct list_head        trigger_list;
>>> +
>>> +       struct list_head        list;
>>> +};
>>> +
>>> +struct iio_counter;
>>> +
>>> +/**
>>> + * struct iio_counter_ops - IIO Counter related callbacks
>>> + * @signal_read:       function to request a signal value from the device.
>>> + *                     Return value will specify the type of value returned by
>>> + *                     the device. val and val2 will contain the elements
>>> + *                     making up the returned value. Note that the counter
>>> + *                     signal_list_lock is acquired before this function is
>>> + *                     called, and released after this function returns.
>>> + * @signal_write:      function to write a signal value to the device.
>>> + *                     Parameters and locking behavior are the same as
>>> + *                     signal_read.
>>> + * @trigger_mode_set:  function to set the trigger mode. mode is the index of
>>> + *                     the requested mode from the value trigger_modes array.
>>> + *                     Note that the counter value_list_lock and value
>>> + *                     trigger_list_lock are acquired before this function is
>>> + *                     called, and released after this function returns.
>>> + * @trigger_mode_get:  function to get the current trigger mode. Return value
>>> + *                     will specify the index of the current mode from the
>>> + *                     value trigger_modes array. Locking behavior is the same
>>> + *                     as trigger_mode_set.
>>> + * @value_read:                function to request a value value from the device.
>>> + *                     Return value will specify the type of value returned by
>>> + *                     the device. val and val2 will contain the elements
>>> + *                     making up the returned value. Note that the counter
>>> + *                     value_list_lock is acquired before this function is
>>> + *                     called, and released after this function returns.
>>> + * @value_write:       function to write a value value to the device.
>>> + *                     Parameters and locking behavior are the same as
>>> + *                     value_read.
>>> + * @value_function_set: function to set the value function mode. mode is the
>>> + *                     index of the requested mode from the value
>>> + *                     function_modes array. Note that the counter
>>> + *                     value_list_lock is acquired before this function is
>>> + *                     called, and released after this function returns.
>>> + * @value_function_get: function to get the current value function mode. Return
>>> + *                     value will specify the index of the current mode from
>>> + *                     the value function_modes array. Locking behavior is the
>>> + *                     same as value_function_get.
>>> + */
>>> +struct iio_counter_ops {
>>> +       int (*signal_read)(struct iio_counter *counter,
>>> +               struct iio_counter_signal *signal, int *val, int *val2);
>>> +       int (*signal_write)(struct iio_counter *counter,
>>> +               struct iio_counter_signal *signal, int val, int val2);
>>> +       int (*trigger_mode_set)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value,
>>> +               struct iio_counter_trigger *trigger, unsigned int mode);
>>> +       int (*trigger_mode_get)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value,
>>> +               struct iio_counter_trigger *trigger);
>>> +       int (*value_read)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value, int *val, int *val2);
>>> +       int (*value_write)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value, int val, int val2);
>>> +       int (*value_function_set)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value, unsigned int mode);
>>> +       int (*value_function_get)(struct iio_counter *counter,
>>> +               struct iio_counter_value *value);
>>> +};

I think it would be more clear if structures iio_counter_signal,
iio_counter_trigger
and iio_counter_value embedded the functions related to their use.
For example struct iio_counter_trigger could have trigger_mode_set and
trigger_mode_get
functions. If you do like that you can remove iio_counter_ops.

Do you think that some functions like get/set counter value, direction
and counter
range (min, max) are generic enough to be included in
iio_counter_value structure ?

>>> +
>>> +/**
>>> + * struct iio_counter - IIO Counter data structure
>>> + * @id:                        [DRIVER] unique ID used to identify counter
>>> + * @name:              [DRIVER] name of the device
>>> + * @dev:               [DRIVER] device structure, should be assigned a parent
>>> + *                     and owner
>>> + * @ops:               [DRIVER] callbacks from driver for counter components
>>> + * @init_signals:      [DRIVER] array of signals for initialization
>>> + * @num_init_signals:  [DRIVER] number of signals specified in @init_signals
>>> + * @init_values:       [DRIVER] array of values for initialization
>>> + * @num_init_values:   [DRIVER] number of values specified in @init_values
>>> + * @signal_list_lock:  [INTERN] lock for accessing @signal_list
>>> + * @signal_list:       [INTERN] list of all signals currently registered to
>>> + *                     counter
>>> + * @value_list_lock:   [INTERN] lock for accessing @value_list
>>> + * @value_list:                [INTERN] list of all values currently registered to
>>> + *                     counter
>>> + * @channels:          [DRIVER] channel specification structure table
>>> + * @num_channels:      [DRIVER] number of channels specified in @channels
>>> + * @info:              [DRIVER] callbacks and constant info from driver
>>> + * @indio_dev:         [INTERN] industrial I/O device structure
>>> + * @driver_data:       [DRIVER] driver data
>>> + */
>>> +struct iio_counter {
>>> +       int                             id;
>>> +       const char                      *name;
>>> +       struct device                   *dev;

id, name and dev are already in struct iio_dev, maybe we can remove them ?

>>> +       const struct iio_counter_ops    *ops;
>>> +
>>> +       struct iio_counter_signal       *init_signals;
>>> +       size_t                          num_init_signals;

I think we can remove init_signals and num_init_signals from this structure
because they are already linked with the values through trigger structure.

>>> +       struct iio_counter_value        *init_values;
>>> +       size_t                          num_init_values;
>>> +
>>> +       struct mutex            signal_list_lock;
>>> +       struct list_head        signal_list;
>>> +       struct mutex            value_list_lock;
>>> +       struct list_head        value_list;
>>> +
>>> +       const struct iio_chan_spec      *channels;
>>> +       size_t                          num_channels;
>>> +       const struct iio_info           *info;
>>> +
>>> +       struct iio_dev  *indio_dev;
>>> +       void            *driver_data;

"driver_data" => "priv" to do like iio_dev

>>> +};
>>> +
>>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const trigger);
>>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const trigger);
>>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers);
>>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>>> +       struct iio_counter_trigger *triggers, size_t num_triggers);
>>> +
>>> +int iio_counter_value_register(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const value);
>>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const value);
>>> +int iio_counter_values_register(struct iio_counter *const counter,
>>> +       struct iio_counter_value *const values, const size_t num_values);
>>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>>> +       struct iio_counter_value *values, size_t num_values);
>>> +
>>> +int iio_counter_register(struct iio_counter *const counter);
>>> +void iio_counter_unregister(struct iio_counter *const counter);
>>> +
>>> +#endif /* CONFIG_IIO_COUNTER */
>>> +
>>> +#endif /* _IIO_COUNTER_H_ */
>>> --
>>> 2.14.1
>>>
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William Breathitt Gray Oct. 4, 2017, 7:12 p.m. UTC | #4

On Tue, Oct 03, 2017 at 04:01:17PM +0200, Benjamin Gaignard wrote:
>2017-09-29 22:01 GMT+02:00 William Breathitt Gray <[e-mail]>:
>> On Fri, Sep 29, 2017 at 03:42:02PM +0200, Benjamin Gaignard wrote:
>>>2017-09-25 20:08 GMT+02:00 William Breathitt Gray <[e-mail]>:
>>>> This patch introduces the IIO generic counter interface for supporting
>>>> counter devices. The generic counter interface serves as a catch-all to
>>>> enable rudimentary support for devices that qualify as counters. More
>>>> specific and apt counter interfaces may be developed on top of the
>>>> generic counter interface, and those interfaces should be used by
>>>> drivers when possible rather than the generic counter interface.
>>>>
>>>> In the context of the IIO generic counter interface, a counter is
>>>> defined as a device that reports one or more "counter values" based on
>>>> the state changes of one or more "counter signals" as evaluated by a
>>>> defined "counter function."
>>>>
>>>> The IIO generic counter interface piggybacks off of the IIO core. This
>>>> is primarily used to leverage the existing sysfs setup: the IIO_COUNT
>>>> channel attributes represent the "counter value," while the IIO_SIGNAL
>>>> channel attributes represent the "counter signal;" auxilary IIO_COUNT
>>>> attributes represent the "counter signal" connections and their
>>>> respective state change configurations which trigger an associated
>>>> "counter function" evaluation.
>>>>
>>>> The iio_counter_ops structure serves as a container for driver callbacks
>>>> to communicate with the device; function callbacks are provided to read
>>>> and write various "counter signals" and "counter values," and set and
>>>> get the "trigger mode" and "function mode" for various "counter signals"
>>>> and "counter values" respectively.
>>>>
>>>> To support a counter device, a driver must first allocate the available
>>>> "counter signals" via iio_counter_signal structures. These "counter
>>>> signals" should be stored as an array and set to the init_signals member
>>>> of an allocated iio_counter structure before the counter is registered.
>>>>
>>>> "Counter values" may be allocated via iio_counter_value structures, and
>>>> respective "counter signal" associations made via iio_counter_trigger
>>>> structures. Initial associated iio_counter_trigger structures may be
>>>> stored as an array and set to the the init_triggers member of the
>>>> respective iio_counter_value structure. These iio_counter_value
>>>> structures may be set to the init_values member of an allocated
>>>> iio_counter structure before the counter is registered if so desired.
>>>>
>>>> A counter device is registered to the system by passing the respective
>>>> initialized iio_counter structure to the iio_counter_register function;
>>>> similarly, the iio_counter_unregister function unregisters the
>>>> respective counter.
>>>>
>>>> Signed-off-by: William Breathitt Gray <[e-mail]>
>>>
>>>Hi William,
>>>
>>>Thanks for your patches, I start try to implement them in stm32-timer driver
>>>but I think it will take me some time before understand all your code.
>>>
>>>I have some warning when compiling the code (see below).
>>
>> Hi Benjamin,
>>
>> Thank you for trying out the patches. I've been focusing on the main API
>> documentation thus far, so unfortunately the current code is still a bit
>> hard to follow -- hopefully I can clean it up some soon. Regardless,
>> I'll be happy to answer any questions you may encounter while reviewing
>> the patches.
>>
>> Regarding the compilation warnings: see my response inline below.
>>
>>>
>>>About wording, I think that using "trigger" to describe signal active
>>>states/edges
>>>could be confusing in IIO context but I haven't found yet a better name.
>>
>> I agree very much with this. "Trigger" was a bad name choice when I
>> developed the Generic Counter paradigm. I would like to come up with a
>> better name for this component before this patchset is merged.
>>
>> The "Trigger" component essentially describes an association between a
>> Signal and Value. The association typically has a defined Signal data
>> condition which triggers the respective Value function operation (or
>> occasionally the trigger condition is just left as "None"), but
>> ultimately it's the association itself that is the key aspect this
>> component.
>>
>> I have considered changing it to "Association" or "Connection" as the
>> name, but both of these seem to sound too vague of terms. I shall keep
>> thinking of various alternative names for this component and change the
>> documentation in a subsequent patchset version once we have a more
>> fitting name.
>
>Yes it isn't easy to find the good name for that, maybe signal capabilities or
>signal behavoir could also be considere.
>
>>
>>>
>>>I also not very sure about what you expect from iio_counter_ops signal_read and
>>>signal_write functions, do you think get/set the value of the signal ?
>>>(i.e read gpio level ?)
>>
>> Yes, for an ordinary simple counter, signal_read and signal_write would
>> typically expose control of the respective hardware input line level.
>>
>> However, it is important to remember that within the context of the
>> Generic Counter paradigm, Signals are abstract components: a single
>> Signal may not directly correlate to a single hardware input line; this
>> is the primary reason for providing the signal_read/signal_write
>> functions.
>>
>> For example, suppose we have a counter with a single Value associated to
>> a single Signal. The Signal data is a 3-bit decimal value, and the Value
>> is an ongoing count of the number of times the Signal data decimal value
>> has had a value greater than "5."
>>
>> The hardware itself could consist of three individual input lines
>> (one for each bit), but there is ultimately only one Signal. In this
>> scenario, I would expect signal_read to simply return the 3-bit decimal
>> value -- not the three physical hardware input line level. Notice the
>> abstraction which has occurred: the Signal is the data represented by
>> the hardware input, but not the raw hardware input itself.
>
>I do not have access to the hardware input value anyway so I will just
>keep those functions empty.

That is a perfectly acceptable practice as many devices do not provide
this data either, so I expect many drivers to lack these definitions.

>
>I have done some progress in driver implementation but I have questions
>and suggestion, see below.
>
>Benjamin
>
>>
>> Sincerely,
>>
>> William Breathitt Gray
>>
>>>
>>>I will continue to review and implement your patches, I hope that end
>>>of next week
>>>have something functionnal to share with you.
>>>
>>>Thansk to have propose this, I do believe it will be helpful
>>>
>>>Benjamin
>>>> ---
>>>>  MAINTAINERS                        |    7 +
>>>>  drivers/iio/Kconfig                |    8 +
>>>>  drivers/iio/Makefile               |    1 +
>>>>  drivers/iio/counter/Kconfig        |    1 +
>>>>  drivers/iio/industrialio-counter.c | 1151 ++++++++++++++++++++++++++++++++++++
>>>>  include/linux/iio/counter.h        |  221 +++++++
>>>>  6 files changed, 1389 insertions(+)
>>>>  create mode 100644 drivers/iio/industrialio-counter.c
>>>>  create mode 100644 include/linux/iio/counter.h
>>>>
>>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>>> index 6f7721d1634c..24fc2dcf1995 100644
>>>> --- a/MAINTAINERS
>>>> +++ b/MAINTAINERS
>>>> @@ -6577,6 +6577,13 @@ F:       Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>>>>  F:     Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
>>>>  F:     drivers/iio/adc/envelope-detector.c
>>>>
>>>> +IIO GENERIC COUNTER INTERFACE
>>>> +M:     William Breathitt Gray <[e-mail]>
>>>> +L:     [e-mail]
>>>> +S:     Maintained
>>>> +F:     drivers/iio/industrialio-counter.c
>>>> +F:     include/linux/iio/counter.h
>>>> +
>>>>  IIO MULTIPLEXER
>>>>  M:     Peter Rosin <[e-mail]>
>>>>  L:     [e-mail]
>>>> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
>>>> index b3c8c6ef0dff..78e01f4f5937 100644
>>>> --- a/drivers/iio/Kconfig
>>>> +++ b/drivers/iio/Kconfig
>>>> @@ -30,6 +30,14 @@ config IIO_CONFIGFS
>>>>           (e.g. software triggers). For more info see
>>>>           Documentation/iio/iio_configfs.txt.
>>>>
>>>> +config IIO_COUNTER
>>>> +       bool "Enable IIO counter support"
>>>> +       help
>>>> +         Provides IIO core support for counters. This API provides
>>>> +         a generic interface that serves as the building blocks to
>>>> +         create more complex counter interfaces. Rudimentary support
>>>> +         for counters is enabled.
>>>> +
>>>>  config IIO_TRIGGER
>>>>         bool "Enable triggered sampling support"
>>>>         help
>>>> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
>>>> index 93c769cd99bf..6427ff38f964 100644
>>>> --- a/drivers/iio/Makefile
>>>> +++ b/drivers/iio/Makefile
>>>> @@ -5,6 +5,7 @@
>>>>  obj-$(CONFIG_IIO) += industrialio.o
>>>>  industrialio-y := industrialio-core.o industrialio-event.o inkern.o
>>>>  industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
>>>> +industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
>>>>  industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
>>>>
>>>>  obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
>>>> diff --git a/drivers/iio/counter/Kconfig b/drivers/iio/counter/Kconfig
>>>> index b37e5fc03149..3d46a790d8db 100644
>>>> --- a/drivers/iio/counter/Kconfig
>>>> +++ b/drivers/iio/counter/Kconfig
>>>> @@ -4,6 +4,7 @@
>>>>  # When adding new entries keep the list in alphabetical order
>>>>
>>>>  menu "Counters"
>>>> +       depends on IIO_COUNTER
>>>>
>>>>  config 104_QUAD_8
>>>>         tristate "ACCES 104-QUAD-8 driver"
>>>> diff --git a/drivers/iio/industrialio-counter.c b/drivers/iio/industrialio-counter.c
>>>> new file mode 100644
>>>> index 000000000000..bdf190d010e4
>>>> --- /dev/null
>>>> +++ b/drivers/iio/industrialio-counter.c
>>>> @@ -0,0 +1,1151 @@
>>>> +/*
>>>> + * Industrial I/O counter interface functions
>>>> + * Copyright (C) 2017 William Breathitt Gray
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License, version 2, as
>>>> + * published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful, but
>>>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>>> + * General Public License for more details.
>>>> + */
>>>> +#include <linux/err.h>
>>>> +#include <linux/export.h>
>>>> +#include <linux/gfp.h>
>>>> +#include <linux/kernel.h>
>>>> +#include <linux/list.h>
>>>> +#include <linux/mutex.h>
>>>> +#include <linux/printk.h>
>>>> +#include <linux/slab.h>
>>>> +#include <linux/string.h>
>>>> +
>>>> +#include <linux/iio/iio.h>
>>>> +#include <linux/iio/types.h>
>>>> +
>>>> +#include <linux/iio/counter.h>
>>>> +
>>>> +static struct iio_counter_signal *iio_counter_signal_find_by_id(
>>>> +       const struct iio_counter *const counter, const int id)
>>>> +{
>>>> +       struct iio_counter_signal *iter;
>>>> +
>>>> +       list_for_each_entry(iter, &counter->signal_list, list)
>>>> +               if (iter->id == id)
>>>> +                       return iter;
>>>> +
>>>> +       return NULL;
>>>> +}
>>>> +
>>>> +static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
>>>> +       const struct iio_counter_value *const value, const int id)
>>>> +{
>>>> +       struct iio_counter_trigger *iter;
>>>> +
>>>> +       list_for_each_entry(iter, &value->trigger_list, list)
>>>> +               if (iter->signal->id == id)
>>>> +                       return iter;
>>>> +
>>>> +       return NULL;
>>>> +}
>>>> +
>>>> +static struct iio_counter_value *iio_counter_value_find_by_id(
>>>> +       const struct iio_counter *const counter, const int id)
>>>> +{
>>>> +       struct iio_counter_value *iter;
>>>> +
>>>> +       list_for_each_entry(iter, &counter->value_list, list)
>>>> +               if (iter->id == id)
>>>> +                       return iter;
>>>> +
>>>> +       return NULL;
>>>> +}
>>>> +
>>>> +static void iio_counter_trigger_unregister_all(
>>>> +       struct iio_counter_value *const value)
>>>> +{
>>>> +       struct iio_counter_trigger *iter, *tmp_iter;
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +       list_for_each_entry_safe(iter, tmp_iter, &value->trigger_list, list)
>>>> +               list_del(&iter->list);
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +}
>>>> +
>>>> +static void iio_counter_signal_unregister_all(struct iio_counter *const counter)
>>>> +{
>>>> +       struct iio_counter_signal *iter, *tmp_iter;
>>>> +
>>>> +       mutex_lock(&counter->signal_list_lock);
>>>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->signal_list, list)
>>>> +               list_del(&iter->list);
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +}
>>>> +
>>>> +static void iio_counter_value_unregister_all(struct iio_counter *const counter)
>>>> +{
>>>> +       struct iio_counter_value *iter, *tmp_iter;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +       list_for_each_entry_safe(iter, tmp_iter, &counter->value_list, list) {
>>>> +               iio_counter_trigger_unregister_all(iter);
>>>> +
>>>> +               list_del(&iter->list);
>>>> +       }
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
>>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       const struct iio_counter_signal *signal;
>>>> +
>>>> +       mutex_lock(&counter->signal_list_lock);
>>>> +       signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +       if (!signal)
>>>> +               return -EINVAL;
>>>> +
>>>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,
>>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       const struct iio_counter_value *value;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +       if (!value)
>>>> +               return -EINVAL;
>>>> +
>>>> +       return scnprintf(buf, PAGE_SIZE, "%s\n", value->name);
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
>>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       const struct iio_counter_trigger *trigger;
>>>> +       ssize_t len = 0;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               len = -EINVAL;
>>>> +               goto err_find_value;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +       list_for_each_entry(trigger, &value->trigger_list, list) {
>>>> +               len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
>>>> +                       trigger->signal->id, trigger->signal->name,
>>>> +                       trigger->trigger_modes[trigger->mode]);
>>>> +               if (len >= PAGE_SIZE) {
>>>> +                       len = -ENOMEM;
>>>> +                       goto err_no_buffer_space;
>>>> +               }
>>>> +       }
>>>> +err_no_buffer_space:
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +err_find_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return len;
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
>>>> +       uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       ssize_t ret;
>>>> +       struct iio_counter_trigger *trigger;
>>>> +       const int signal_id = *(int *)((void *)priv);
>>>> +       int mode;
>>>> +
>>>> +       if (!counter->ops->trigger_mode_get)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               ret = -EINVAL;
>>>> +               goto err_value;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +
>>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>>> +       if (!trigger) {
>>>> +               ret = -EINVAL;
>>>> +               goto err_trigger;
>>>> +       }
>>>> +
>>>> +       mode = counter->ops->trigger_mode_get(counter, value, trigger);
>>>> +
>>>> +       if (mode < 0) {
>>>> +               ret = mode;
>>>> +               goto err_trigger;
>>>> +       } else if (mode >= trigger->num_trigger_modes) {
>>>> +               ret = -EINVAL;
>>>> +               goto err_trigger;
>>>> +       }
>>>> +
>>>> +       trigger->mode = mode;
>>>> +
>>>> +       ret = scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
>>>> +
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return ret;
>>>> +
>>>> +err_trigger:
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +err_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +       return ret;
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
>>>> +       uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
>>>> +       size_t len)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       ssize_t err;
>>>> +       struct iio_counter_trigger *trigger;
>>>> +       const int signal_id = *(int *)((void *)priv);
>>>> +       unsigned int mode;
>>>> +
>>>> +       if (!counter->ops->trigger_mode_set)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               err = -EINVAL;
>>>> +               goto err_value;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +
>>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>>> +       if (!trigger) {
>>>> +               err = -EINVAL;
>>>> +               goto err_trigger;
>>>> +       }
>>>> +
>>>> +       for (mode = 0; mode < trigger->num_trigger_modes; mode++)
>>>> +               if (sysfs_streq(buf, trigger->trigger_modes[mode]))
>>>> +                       break;
>>>> +
>>>> +       if (mode >= trigger->num_trigger_modes) {
>>>> +               err = -EINVAL;
>>>> +               goto err_trigger;
>>>> +       }
>>>> +
>>>> +       err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
>>>> +       if (err)
>>>> +               goto err_trigger;
>>>> +
>>>> +       trigger->mode = mode;
>>>> +
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return len;
>>>> +
>>>> +err_trigger:
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +err_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static ssize_t iio_counter_trigger_mode_available_read(
>>>> +       struct iio_dev *indio_dev, uintptr_t priv,
>>>> +       const struct iio_chan_spec *chan, char *buf)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       ssize_t len = 0;
>>>> +       struct iio_counter_trigger *trigger;
>>>> +       const int signal_id = *(int *)((void *)priv);
>>>> +       unsigned int i;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               len = -EINVAL;
>>>> +               goto err_no_value;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +
>>>> +       trigger = iio_counter_trigger_find_by_id(value, signal_id);
>>>> +       if (!trigger) {
>>>> +               len = -EINVAL;
>>>> +               goto err_no_trigger;
>>>> +       }
>>>> +
>>>> +       for (i = 0; i < trigger->num_trigger_modes; i++)
>>>> +               len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
>>>> +                       trigger->trigger_modes[i]);
>>>> +
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       buf[len - 1] = '\n';
>>>> +
>>>> +       return len;
>>>> +
>>>> +err_no_trigger:
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +err_no_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +       return len;
>>>> +}
>>>> +
>>>> +static int iio_counter_value_function_set(struct iio_dev *indio_dev,
>>>> +       const struct iio_chan_spec *chan, unsigned int mode)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       int err;
>>>> +
>>>> +       if (!counter->ops->value_function_set)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               err = -EINVAL;
>>>> +               goto err_value;
>>>> +       }
>>>> +
>>>> +       err = counter->ops->value_function_set(counter, value, mode);
>>>> +       if (err)
>>>> +               goto err_value;
>>>> +
>>>> +       value->mode = mode;
>>>> +
>>>> +err_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static int iio_counter_value_function_get(struct iio_dev *indio_dev,
>>>> +       const struct iio_chan_spec *chan)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_value *value;
>>>> +       int retval;
>>>> +
>>>> +       if (!counter->ops->value_function_get)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +       if (!value) {
>>>> +               retval = -EINVAL;
>>>> +               goto err_value;
>>>> +       }
>>>> +
>>>> +       retval = counter->ops->value_function_get(counter, value);
>>>> +       if (retval < 0)
>>>> +               goto err_value;
>>>> +       else if (retval >= value->num_function_modes) {
>>>> +               retval = -EINVAL;
>>>> +               goto err_value;
>>>> +       }
>>>> +
>>>> +       value->mode = retval;
>>>> +
>>>> +err_value:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return retval;
>>>> +}
>>>> +
>>>> +static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
>>>> +       struct iio_counter_value *const value)
>>>> +{
>>>> +       const struct iio_chan_spec_ext_info ext_info_default[] = {
>>>> +               {
>>>> +                       .name = "name",
>>>> +                       .shared = IIO_SEPARATE,
>>>> +                       .read = iio_counter_value_name_read
>>>> +               },
>>>> +               IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
>>>> +               {
>>>> +                       .name = "function_available",
>>>> +                       .shared = IIO_SEPARATE,
>>>> +                       .read = iio_enum_available_read,
>>>> +                       .private = (void *)&value->function_enum
>>>I have this warning the 3 times that  private field is set
>>>drivers/iio/industrialio-counter.c:401:15: warning: initialization
>>>makes integer from pointer without a cast [-Wint-conversion]
>>>    .private = (void *)&value->function_enum
>>>
>>>I think you can change it to "void *" instead of a uintptr_t
>>
>> These are pretty benign warnings which you may ignore: I'm doing an
>> implicit conversion to uintptr_t which is ultimately an integer type; in
>> general, pointer to integer conversations are unsafe, but there is a
>> special exception in the C language for the uintptr_t data type. I could
>> have used an explicit cast to avoid the warning but opted to leave it
>> implicit to keep the code easier to read.
>>
>> However, it would be nice if the private member was void *, since the
>> intent of my code would be clearer in that case (passing a pointer for
>> later dereference). Unfortunately, I'm hesitant to submit a patch to
>> change the "private" member data type to void * since other drivers may
>> require the uintptr_t data type -- my suspicion is that there are some
>> drivers out there which do since the choice to introduce the "private"
>> member as a uintptr_t appears deliberate.
>>
>>>> +               },
>>>> +               {
>>>> +                       .name = "triggers",
>>>> +                       .shared = IIO_SEPARATE,
>>>> +                       .read = iio_counter_value_triggers_read
>>>> +               }
>>>> +       };
>>>> +       const size_t num_default = ARRAY_SIZE(ext_info_default);
>>>> +       const struct iio_chan_spec_ext_info ext_info_trigger[] = {
>>>> +               {
>>>> +                       .shared = IIO_SEPARATE,
>>>> +                       .read = iio_counter_trigger_mode_read,
>>>> +                       .write = iio_counter_trigger_mode_write
>>>> +               },
>>>> +               {
>>>> +                       .shared = IIO_SEPARATE,
>>>> +                       .read = iio_counter_trigger_mode_available_read
>>>> +               }
>>>> +       };
>>>> +       const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
>>>> +       const struct list_head *pos;
>>>> +       size_t num_triggers = 0;
>>>> +       size_t num_triggers_ext_info;
>>>> +       size_t num_ext_info;
>>>> +       int err;
>>>> +       struct iio_chan_spec_ext_info *ext_info;
>>>> +       const struct iio_counter_trigger *trigger_pos;
>>>> +       size_t i;
>>>> +
>>>> +       value->function_enum.items = value->function_modes;
>>>> +       value->function_enum.num_items = value->num_function_modes;
>>>> +       value->function_enum.set = iio_counter_value_function_set;
>>>> +       value->function_enum.get = iio_counter_value_function_get;
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +
>>>> +       list_for_each(pos, &value->trigger_list)
>>>> +               num_triggers++;
>>>> +
>>>> +       num_triggers_ext_info = num_ext_info_trigger * num_triggers;
>>>> +       num_ext_info = num_default + num_triggers_ext_info + 1;
>>>> +
>>>> +       ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
>>>> +       if (!ext_info) {
>>>> +               err = -ENOMEM;
>>>> +               goto err_ext_info_alloc;
>>>> +       }
>>>> +       ext_info[num_ext_info - 1].name = NULL;
>>>> +
>>>> +       memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
>>>> +       for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
>>>> +               memcpy(ext_info + num_default + i, ext_info_trigger,
>>>> +                       sizeof(ext_info_trigger));
>>>> +
>>>> +       i = num_default;
>>>> +       list_for_each_entry(trigger_pos, &value->trigger_list, list) {
>>>> +               ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
>>>> +                       chan->channel, trigger_pos->signal->id);
>>>> +               if (!ext_info[i].name) {
>>>> +                       err = -ENOMEM;
>>>> +                       goto err_name_alloc;
>>>> +               }
>>>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>>>> +               i++;
>>>> +
>>>> +               ext_info[i].name = kasprintf(GFP_KERNEL,
>>>> +                       "trigger_signal%d-%d_available",
>>>> +                       chan->channel, trigger_pos->signal->id);
>>>> +               if (!ext_info[i].name) {
>>>> +                       err = -ENOMEM;
>>>> +                       goto err_name_alloc;
>>>> +               }
>>>> +               ext_info[i].private = (void *)&trigger_pos->signal->id;
>>>> +               i++;
>>>> +       }
>>>> +
>>>> +       chan->ext_info = ext_info;
>>>> +
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_name_alloc:
>>>> +       while (i-- > num_default)
>>>> +               kfree(ext_info[i].name);
>>>> +       kfree(ext_info);
>>>> +err_ext_info_alloc:
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static void iio_counter_value_ext_info_free(
>>>> +       const struct iio_chan_spec *const channel)
>>>> +{
>>>> +       size_t i;
>>>> +       const char *const prefix = "trigger_signal";
>>>> +       const size_t prefix_len = strlen(prefix);
>>>> +
>>>> +       for (i = 0; channel->ext_info[i].name; i++)
>>>> +               if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
>>>> +                       kfree(channel->ext_info[i].name);
>>>> +       kfree(channel->ext_info);
>>>> +}
>>>> +
>>>> +static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
>>>> +       {
>>>> +               .name = "name",
>>>> +               .shared = IIO_SEPARATE,
>>>> +               .read = iio_counter_signal_name_read
>>>> +       },
>>>> +       {}
>>>> +};
>>>> +
>>>> +static int iio_counter_channels_alloc(struct iio_counter *const counter)
>>>> +{
>>>> +       const struct list_head *pos;
>>>> +       size_t num_channels = 0;
>>>> +       int err;
>>>> +       struct iio_chan_spec *channels;
>>>> +       struct iio_counter_value *value_pos;
>>>> +       size_t i = counter->num_channels;
>>>> +       const struct iio_counter_signal *signal_pos;
>>>> +
>>>> +       mutex_lock(&counter->signal_list_lock);
>>>> +
>>>> +       list_for_each(pos, &counter->signal_list)
>>>> +               num_channels++;
>>>> +
>>>> +       if (!num_channels) {
>>>> +               err = -EINVAL;
>>>> +               goto err_no_signals;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +
>>>> +       list_for_each(pos, &counter->value_list)
>>>> +               num_channels++;
>>>> +
>>>> +       num_channels += counter->num_channels;
>>>> +
>>>> +       channels = kcalloc(num_channels, sizeof(*channels), GFP_KERNEL);
>>>> +       if (!channels) {
>>>> +               err = -ENOMEM;
>>>> +               goto err_channels_alloc;
>>>> +       }
>>>> +
>>>> +       memcpy(channels, counter->channels,
>>>> +               counter->num_channels * sizeof(*counter->channels));
>>>> +
>>>> +       list_for_each_entry(value_pos, &counter->value_list, list) {
>>>> +               channels[i].type = IIO_COUNT;
>>>> +               channels[i].channel = counter->id;
>>>> +               channels[i].channel2 = value_pos->id;
>>>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>>>> +               channels[i].indexed = 1;
>>>> +               channels[i].counter = 1;
>>>> +
>>>> +               err = iio_counter_value_ext_info_alloc(channels + i, value_pos);
>>>> +               if (err)
>>>> +                       goto err_value_ext_info_alloc;
>>>> +
>>>> +               i++;
>>>> +       }
>>>> +
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       list_for_each_entry(signal_pos, &counter->signal_list, list) {
>>>> +               channels[i].type = IIO_SIGNAL;
>>>> +               channels[i].channel = counter->id;
>>>> +               channels[i].channel2 = signal_pos->id;
>>>> +               channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
>>>> +               channels[i].indexed = 1;
>>>> +               channels[i].counter = 1;
>>>> +               channels[i].ext_info = iio_counter_signal_ext_info;
>>>> +
>>>> +               i++;
>>>> +       }
>>>> +
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +
>>>> +       counter->indio_dev->num_channels = num_channels;
>>>> +       counter->indio_dev->channels = channels;
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_value_ext_info_alloc:
>>>> +       while (i-- > counter->num_channels)
>>>> +               iio_counter_value_ext_info_free(channels + i);
>>>> +       kfree(channels);
>>>> +err_channels_alloc:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +err_no_signals:
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static void iio_counter_channels_free(const struct iio_counter *const counter)
>>>> +{
>>>> +       size_t i = counter->num_channels + counter->indio_dev->num_channels;
>>>> +       const struct iio_chan_spec *const chans = counter->indio_dev->channels;
>>>> +
>>>> +       while (i-- > counter->num_channels)
>>>> +               if (chans[i].type == IIO_COUNT)
>>>> +                       iio_counter_value_ext_info_free(chans + i);
>>>> +
>>>> +       kfree(chans);
>>>> +}
>>>> +
>>>> +static int iio_counter_read_raw(struct iio_dev *indio_dev,
>>>> +       struct iio_chan_spec const *chan, int *val, int *val2, long mask)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_signal *signal;
>>>> +       int retval;
>>>> +       struct iio_counter_value *value;
>>>> +
>>>> +       if (mask != IIO_CHAN_INFO_RAW)
>>>> +               return -EINVAL;
>>>> +
>>>> +       switch (chan->type) {
>>>> +       case IIO_SIGNAL:
>>>> +               if (!counter->ops->signal_read)
>>>> +                       return -EINVAL;
>>>> +
>>>> +               mutex_lock(&counter->signal_list_lock);
>>>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>>> +               if (!signal) {
>>>> +                       mutex_unlock(&counter->signal_list_lock);
>>>> +                       return -EINVAL;
>>>> +               }
>>>> +
>>>> +               retval = counter->ops->signal_read(counter, signal, val, val2);
>>>> +               mutex_unlock(&counter->signal_list_lock);
>>>> +
>>>> +               return retval;
>>>> +       case IIO_COUNT:
>>>> +               if (!counter->ops->value_read)
>>>> +                       return -EINVAL;
>>>> +
>>>> +               mutex_lock(&counter->value_list_lock);
>>>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +               if (!value) {
>>>> +                       mutex_unlock(&counter->value_list_lock);
>>>> +                       return -EINVAL;
>>>> +               }
>>>> +
>>>> +               retval = counter->ops->value_read(counter, value, val, val2);
>>>> +               mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +               return retval;
>>>> +       default:
>>>> +               if (counter->info && counter->info->read_raw)
>>>> +                       return counter->info->read_raw(indio_dev, chan, val,
>>>> +                               val2, mask);
>>>> +       }
>>>> +
>>>> +       return -EINVAL;
>>>> +}
>>>> +
>>>> +static int iio_counter_write_raw(struct iio_dev *indio_dev,
>>>> +       struct iio_chan_spec const *chan, int val, int val2, long mask)
>>>> +{
>>>> +       struct iio_counter *const counter = iio_priv(indio_dev);
>>>> +       struct iio_counter_signal *signal;
>>>> +       int retval;
>>>> +       struct iio_counter_value *value;
>>>> +
>>>> +       if (mask != IIO_CHAN_INFO_RAW)
>>>> +               return -EINVAL;
>
>I have an issue with this check because I believe it make impossible to call
>the callback registered in iio_info since the channel isn't always
>IIO_CHAN_INFO_RAW
>but could be  IIO_CHAN_INFO_ENABLE or IIO_CHAN_INFO_SCALE in my driver.
>Maybe it is comming from my code be I don't understand how it could
>works in 104-quad-8 either

This may be a bug I overlooked because my intention is to pass
non-counter channels directly to write_raw. I will inspect this more
throughly when I finish the next version of this patchset.

>
>>>> +
>>>> +       switch (chan->type) {
>>>> +       case IIO_SIGNAL:
>>>> +               if (!counter->ops->signal_write)
>>>> +                       return -EINVAL;
>>>> +
>>>> +               mutex_lock(&counter->signal_list_lock);
>>>> +               signal = iio_counter_signal_find_by_id(counter, chan->channel2);
>>>> +               if (!signal) {
>>>> +                       mutex_unlock(&counter->signal_list_lock);
>>>> +                       return -EINVAL;
>>>> +               }
>>>> +
>>>> +               retval = counter->ops->signal_write(counter, signal, val, val2);
>>>> +               mutex_unlock(&counter->signal_list_lock);
>>>> +
>>>> +               return retval;
>>>> +       case IIO_COUNT:
>>>> +               if (!counter->ops->value_write)
>>>> +                       return -EINVAL;
>>>> +
>>>> +               mutex_lock(&counter->value_list_lock);
>>>> +               value = iio_counter_value_find_by_id(counter, chan->channel2);
>>>> +               if (!value) {
>>>> +                       mutex_unlock(&counter->value_list_lock);
>>>> +                       return -EINVAL;
>>>> +               }
>>>> +
>>>> +               retval = counter->ops->value_write(counter, value, val, val2);
>>>> +               mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +               return retval;
>>>> +       default:
>>>> +               if (counter->info && counter->info->write_raw)
>>>> +                       return counter->info->write_raw(indio_dev, chan, val,
>>>> +                               val2, mask);
>>>> +       }
>>>> +
>>>> +       return -EINVAL;
>>>> +}
>>>> +
>>>> +static int iio_counter_signal_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_signal *const signal)
>>>> +{
>>>> +       int err;
>>>> +
>>>> +       if (!counter || !signal)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&counter->signal_list_lock);
>>>> +       if (iio_counter_signal_find_by_id(counter, signal->id)) {
>>>> +               pr_err("Duplicate counter signal ID '%d'\n", signal->id);
>>>> +               err = -EEXIST;
>>>> +               goto err_duplicate_id;
>>>> +       }
>>>> +       list_add_tail(&signal->list, &counter->signal_list);
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_duplicate_id:
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static void iio_counter_signal_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_signal *const signal)
>>>> +{
>>>> +       if (!counter || !signal)
>>>> +               return;
>>>> +
>>>> +       mutex_lock(&counter->signal_list_lock);
>>>> +       list_del(&signal->list);
>>>> +       mutex_unlock(&counter->signal_list_lock);
>>>> +}
>>>> +
>>>> +static int iio_counter_signals_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_signal *const signals, const size_t num_signals)
>>>> +{
>>>> +       size_t i;
>>>> +       int err;
>>>> +
>>>> +       if (!counter || !signals)
>>>> +               return -EINVAL;
>>>> +
>>>> +       for (i = 0; i < num_signals; i++) {
>>>> +               err = iio_counter_signal_register(counter, signals + i);
>>>> +               if (err)
>>>> +                       goto err_signal_register;
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_signal_register:
>>>> +       while (i--)
>>>> +               iio_counter_signal_unregister(counter, signals + i);
>>>> +       return err;
>>>> +}
>>>> +
>>>> +static void iio_counter_signals_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_signal *signals, size_t num_signals)
>>>> +{
>>>> +       if (!counter || !signals)
>>>> +               return;
>>>> +
>>>> +       while (num_signals--) {
>>>> +               iio_counter_signal_unregister(counter, signals);
>>>> +               signals++;
>>>> +       }
>>>> +}
>>>> +
>>>> +/**
>>>> + * iio_counter_trigger_register - register Trigger to Value
>>>> + * @value: pointer to IIO Counter Value for association
>>>> + * @trigger: pointer to IIO Counter Trigger to register
>>>> + *
>>>> + * The Trigger is added to the Value's trigger_list. A check is first performed
>>>> + * to verify that the respective Signal is not already linked to the Value; if
>>>> + * the respective Signal is already linked to the Value, the Trigger is not
>>>> + * added to the Value's trigger_list.
>>>> + *
>>>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>>>> + * during execution.
>>>> + */
>>>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const trigger)
>>>> +{
>>>> +       if (!value || !trigger || !trigger->signal)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +       if (iio_counter_trigger_find_by_id(value, trigger->signal->id)) {
>>>> +               pr_err("Signal%d is already linked to counter value%d\n",
>>>> +                       trigger->signal->id, value->id);
>>>> +               return -EEXIST;
>>>> +       }
>>>> +       list_add_tail(&trigger->list, &value->trigger_list);
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +
>>>> +       return 0;
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_trigger_register);
>>>> +
>>>> +/**
>>>> + * iio_counter_trigger_unregister - unregister Trigger from Value
>>>> + * @value: pointer to IIO Counter Value of association
>>>> + * @trigger: pointer to IIO Counter Trigger to unregister
>>>> + *
>>>> + * The Trigger is removed from the Value's trigger_list.
>>>> + *
>>>> + * NOTE: This function will acquire and release the Value's trigger_list_lock
>>>> + * during execution.
>>>> + */
>>>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const trigger)
>>>> +{
>>>> +       if (!value || !trigger || !trigger->signal)
>>>> +               return;
>>>> +
>>>> +       mutex_lock(&value->trigger_list_lock);
>>>> +       list_del(&trigger->list);
>>>> +       mutex_unlock(&value->trigger_list_lock);
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_trigger_unregister);
>>>> +
>>>> +/**
>>>> + * iio_counter_triggers_register - register an array of Triggers to Value
>>>> + * @value: pointer to IIO Counter Value for association
>>>> + * @triggers: array of pointers to IIO Counter Triggers to register
>>>> + *
>>>> + * The iio_counter_trigger_register function is called for each Trigger in the
>>>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>>>> + *
>>>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>>>> + */
>>>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers)
>>>> +{
>>>> +       size_t i;
>>>> +       int err;
>>>> +
>>>> +       if (!value || !triggers)
>>>> +               return -EINVAL;
>>>> +
>>>> +       for (i = 0; i < num_triggers; i++) {
>>>> +               err = iio_counter_trigger_register(value, triggers + i);
>>>> +               if (err)
>>>> +                       goto err_trigger_register;
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_trigger_register:
>>>> +       while (i--)
>>>> +               iio_counter_trigger_unregister(value, triggers + i);
>>>> +       return err;
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_triggers_register);
>>>> +
>>>> +/**
>>>> + * iio_counter_triggers_unregister - unregister Triggers from Value
>>>> + * @value: pointer to IIO Counter Value of association
>>>> + * @triggers: array of pointers to IIO Counter Triggers to unregister
>>>> + *
>>>> + * The iio_counter_trigger_unregister function is called for each Trigger in the
>>>> + * array. The @triggers array is traversed for the first @num_triggers Triggers.
>>>> + *
>>>> + * NOTE: @num_triggers must not be greater than the size of the @triggers array.
>>>> + */
>>>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *triggers, size_t num_triggers)
>>>> +{
>>>> +       if (!value || !triggers)
>>>> +               return;
>>>> +
>>>> +       while (num_triggers--) {
>>>> +               iio_counter_trigger_unregister(value, triggers);
>>>> +               triggers++;
>>>> +       }
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_triggers_unregister);
>>>> +
>>>> +/**
>>>> + * iio_counter_value_register - register Value to Counter
>>>> + * @counter: pointer to IIO Counter for association
>>>> + * @value: pointer to IIO Counter Value to register
>>>> + *
>>>> + * The registration process occurs in two major steps. First, the Value is
>>>> + * initialized: trigger_list_lock is initialized, trigger_list is initialized,
>>>> + * and init_triggers if not NULL is passed to iio_counter_triggers_register.
>>>> + * Second, the Value is added to the Counter's value_list. A check is first
>>>> + * performed to verify that the Value is not already associated to the Counter
>>>> + * (via the Value's unique ID); if the Value is already associated to the
>>>> + * Counter, the Value is not added to the Counter's value_list and all of the
>>>> + * Value's Triggers are unregistered.
>>>> + *
>>>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>>>> + * during execution.
>>>> + */
>>>> +int iio_counter_value_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const value)
>>>> +{
>>>> +       int err;
>>>> +
>>>> +       if (!counter || !value)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_init(&value->trigger_list_lock);
>>>> +       INIT_LIST_HEAD(&value->trigger_list);
>>>> +
>>>> +       if (value->init_triggers) {
>>>> +               err = iio_counter_triggers_register(value,
>>>> +                       value->init_triggers, value->num_init_triggers);
>>>> +               if (err)
>>>> +                       return err;
>>>> +       }
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +       if (iio_counter_value_find_by_id(counter, value->id)) {
>>>> +               pr_err("Duplicate counter value ID '%d'\n", value->id);
>>>> +               err = -EEXIST;
>>>> +               goto err_duplicate_id;
>>>> +       }
>>>> +       list_add_tail(&value->list, &counter->value_list);
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_duplicate_id:
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +       iio_counter_trigger_unregister_all(value);
>>>> +       return err;
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_value_register);
>>>> +
>>>> +/**
>>>> + * iio_counter_value_unregister - unregister Value from Counter
>>>> + * @counter: pointer to IIO Counter of association
>>>> + * @value: pointer to IIO Counter Value to unregister
>>>> + *
>>>> + * The Value is removed from the Counter's value_list and all of the Value's
>>>> + * Triggers are unregistered.
>>>> + *
>>>> + * NOTE: This function will acquire and release the Counter's value_list_lock
>>>> + * during execution.
>>>> + */
>>>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const value)
>>>> +{
>>>> +       if (!counter || !value)
>>>> +               return;
>>>> +
>>>> +       mutex_lock(&counter->value_list_lock);
>>>> +       list_del(&value->list);
>>>> +       mutex_unlock(&counter->value_list_lock);
>>>> +
>>>> +       iio_counter_trigger_unregister_all(value);
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_value_unregister);
>>>> +
>>>> +/**
>>>> + * iio_counter_values_register - register an array of Values to Counter
>>>> + * @counter: pointer to IIO Counter for association
>>>> + * @values: array of pointers to IIO Counter Values to register
>>>> + *
>>>> + * The iio_counter_value_register function is called for each Value in the
>>>> + * array. The @values array is traversed for the first @num_values Values.
>>>> + *
>>>> + * NOTE: @num_values must not be greater than the size of the @values array.
>>>> + */
>>>> +int iio_counter_values_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const values, const size_t num_values)
>>>> +{
>>>> +       size_t i;
>>>> +       int err;
>>>> +
>>>> +       if (!counter || !values)
>>>> +               return -EINVAL;
>>>> +
>>>> +       for (i = 0; i < num_values; i++) {
>>>> +               err = iio_counter_value_register(counter, values + i);
>>>> +               if (err)
>>>> +                       goto err_values_register;
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_values_register:
>>>> +       while (i--)
>>>> +               iio_counter_value_unregister(counter, values + i);
>>>> +       return err;
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_values_register);
>>>> +
>>>> +/**
>>>> + * iio_counter_values_unregister - unregister Values from Counter
>>>> + * @counter: pointer to IIO Counter of association
>>>> + * @values: array of pointers to IIO Counter Values to unregister
>>>> + *
>>>> + * The iio_counter_value_unregister function is called for each Value in the
>>>> + * array. The @values array is traversed for the first @num_values Values.
>>>> + *
>>>> + * NOTE: @num_values must not be greater than the size of the @values array.
>>>> + */
>>>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *values, size_t num_values)
>>>> +{
>>>> +       if (!counter || !values)
>>>> +               return;
>>>> +
>>>> +       while (num_values--) {
>>>> +               iio_counter_value_unregister(counter, values);
>>>> +               values++;
>>>> +       }
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_values_unregister);
>>>> +
>>>> +/**
>>>> + * iio_counter_register - register Counter to the system
>>>> + * @counter: pointer to IIO Counter to register
>>>> + *
>>>> + * This function piggybacks off of iio_device_register. First, the relevant
>>>> + * Counter members are initialized; if init_signals is not NULL it is passed to
>>>> + * iio_counter_signals_register, and similarly if init_values is not NULL it is
>>>> + * passed to iio_counter_values_register. Next, a struct iio_dev is allocated by
>>>> + * a call to iio_device_alloc and initialized for the Counter, IIO channels are
>>>> + * allocated, the Counter is copied as the private data, and finally
>>>> + * iio_device_register is called.
>>>> + */
>>>> +int iio_counter_register(struct iio_counter *const counter)
>>>> +{
>>>> +       const struct iio_info info_default = {
>>>> +               .read_raw = iio_counter_read_raw,
>>>> +               .write_raw = iio_counter_write_raw
>>>> +       };
>>>> +       int err;
>>>> +       struct iio_info *info;
>>>> +       struct iio_counter *priv;
>>>> +
>>>> +       if (!counter)
>>>> +               return -EINVAL;
>>>> +
>>>> +       mutex_init(&counter->signal_list_lock);
>>>> +       INIT_LIST_HEAD(&counter->signal_list);
>>>> +
>>>> +       if (counter->init_signals) {
>>>> +               err = iio_counter_signals_register(counter,
>>>> +                       counter->init_signals, counter->num_init_signals);
>>>> +               if (err)
>>>> +                       return err;
>>>> +       }
>>>> +
>>>> +       mutex_init(&counter->value_list_lock);
>>>> +       INIT_LIST_HEAD(&counter->value_list);
>>>> +
>>>> +       if (counter->init_values) {
>>>> +               err = iio_counter_values_register(counter,
>>>> +                       counter->init_values, counter->num_init_values);
>>>> +               if (err)
>>>> +                       goto err_values_register;
>>>> +       }
>>>> +
>>>> +       counter->indio_dev = iio_device_alloc(sizeof(*counter));
>>>> +       if (!counter->indio_dev) {
>>>> +               err = -ENOMEM;
>>>> +               goto err_iio_device_alloc;
>>>> +       }
>>>> +
>>>> +       info = kmalloc(sizeof(*info), GFP_KERNEL);
>>>> +       if (!info) {
>>>> +               err = -ENOMEM;
>>>> +               goto err_info_alloc;
>>>> +       }
>>>> +       if (counter->info) {
>>>> +               memcpy(info, counter->info, sizeof(*counter->info));
>>>> +               info->read_raw = iio_counter_read_raw;
>>>> +               info->write_raw = iio_counter_write_raw;
>>>> +       } else {
>>>> +               memcpy(info, &info_default, sizeof(info_default));
>>>> +       }
>>>> +
>>>> +       counter->indio_dev->info = info;
>>>> +       counter->indio_dev->modes = INDIO_DIRECT_MODE;
>
>For stm32 triggerd river I need to be able to change indio_dev->modes
>to INDIO_HARDWARE_TRIGGERED
>Could you add a parameter to be able to configure teh modes ?

The more time I work on the Generic Counter interface, the more I want
to separate the IIO core components from it. I feel that embedding the
iio_dev to the iio_counter structure ends up restricting the
configurability of IIO core components as you have encountered here. I
also fear the possibility of API coupling issues down the road, where
IIO core functionality modifications will lead to a snowball effect of
changes to the Generic Counter iterface (and subsequent derivative
Counter classes) in order to maintain compatibility.

This is an architectural decision I have to make before we merge, so
I'll give it some thought throughout this process. For now, I will
consider adding a modes member to struct iio_counter so that you may
configure indio_dev->modes; this will likely be introduced in version 4
of this patchset after the higher-level paradigm has been solidified.

>
>>>> +       counter->indio_dev->name = counter->name;
>>>> +       counter->indio_dev->dev.parent = counter->dev;
>>>> +
>>>> +       err = iio_counter_channels_alloc(counter);
>>>> +       if (err)
>>>> +               goto err_channels_alloc;
>>>> +
>>>> +       priv = iio_priv(counter->indio_dev);
>>>> +       memcpy(priv, counter, sizeof(*priv));
>>>> +
>>>> +       err = iio_device_register(priv->indio_dev);
>>>> +       if (err)
>>>> +               goto err_iio_device_register;
>>>> +
>>>> +       return 0;
>>>> +
>>>> +err_iio_device_register:
>>>> +       iio_counter_channels_free(counter);
>>>> +err_channels_alloc:
>>>> +       kfree(info);
>>>> +err_info_alloc:
>>>> +       iio_device_free(counter->indio_dev);
>>>> +err_iio_device_alloc:
>>>> +       iio_counter_values_unregister(counter, counter->init_values,
>>>> +               counter->num_init_values);
>>>> +err_values_register:
>>>> +       iio_counter_signals_unregister(counter, counter->init_signals,
>>>> +               counter->num_init_signals);
>>>> +       return err;
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_register);
>>>> +
>>>> +/**
>>>> + * iio_counter_unregister - unregister Counter from the system
>>>> + * @counter: pointer to IIO Counter to unregister
>>>> + *
>>>> + * The Counter is unregistered from the system. The indio_dev is unregistered,
>>>> + * allocated memory is freed, and all associated Values and Signals are
>>>> + * unregistered.
>>>> + */
>>>> +void iio_counter_unregister(struct iio_counter *const counter)
>>>> +{
>>>> +       const struct iio_info *const info = counter->indio_dev->info;
>>>> +
>>>> +       if (!counter)
>>>> +               return;
>>>> +
>>>> +       iio_device_unregister(counter->indio_dev);
>>>> +
>>>> +       iio_counter_channels_free(counter);
>>>> +
>>>> +       kfree(info);
>>>> +       iio_device_free(counter->indio_dev);
>>>> +
>>>> +       iio_counter_value_unregister_all(counter);
>>>> +       iio_counter_signal_unregister_all(counter);
>>>> +}
>>>> +EXPORT_SYMBOL(iio_counter_unregister);
>
>I have added devm_iio_counter_register and devm_iio_counter_unregister to avoid
>add remove in driver code. If that make sense for you can add tehm in your code
>/**
> * devm_iio_counter_register - Resource-managed iio_counter_register()
> * @dev: Device to allocate iio_dev for
> * @counter: pointer to IIO Counter to register
> *
> * Managed iio_counter_register.  The IIO counter registered with this
> * function is automatically unregistered on driver detach. This function
> * calls iio_counter_register() internally. Refer to that function for more
> * information.
> *
> * If an iio counter registered with this function needs to be unregistered
> * separately, devm_iio_counter_unregister() must be used.
> *
> * RETURNS:
> * 0 on success, negative error number on failure.
> */
>int devm_iio_counter_register(struct device *dev,
>      struct iio_counter *const counter)
>{
>struct iio_counter **ptr;
>int ret;
>
>ptr = devres_alloc(devm_iio_counter_unreg, sizeof(*ptr), GFP_KERNEL);
>if (!ptr)
>return -ENOMEM;
>
>*ptr = counter;
>ret = iio_counter_register(counter);
>if (!ret)
>devres_add(dev, ptr);
>else
>devres_free(ptr);
>
>return ret;
>
>}
>EXPORT_SYMBOL(devm_iio_counter_register);
>
>static int devm_iio_counter_match(struct device *dev, void *res, void *data)
>{
>struct iio_counter **r = res;
>if (!r || !*r) {
>WARN_ON(!r || !*r);
>return 0;
>}
>return *r == data;
>}
>
>/**
> * devm_iio_counter_unregister - Resource-managed iio_counter_unregister()
> * @dev: Device this iio_dev belongs to
> * @counter: the iio counter associated with the device
> *
> * Unregister iio counter registered with devm_iio_counter_register().
> */
>void devm_iio_counter_unregister(struct device *dev,
>struct iio_counter *const counter)
>{
>int rc;
>
>rc = devres_release(dev, devm_iio_counter_unreg,
>    devm_iio_counter_match, counter);
>WARN_ON(rc);
>}
>EXPORT_SYMBOL(devm_iio_counter_unregister);

Thanks! I will incorporate this code into the patchset. :)

>
>>>> diff --git a/include/linux/iio/counter.h b/include/linux/iio/counter.h
>>>> new file mode 100644
>>>> index 000000000000..1c1ca13a6053
>>>> --- /dev/null
>>>> +++ b/include/linux/iio/counter.h
>>>> @@ -0,0 +1,221 @@
>>>> +/*
>>>> + * Industrial I/O counter interface
>>>> + * Copyright (C) 2017 William Breathitt Gray
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License, version 2, as
>>>> + * published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful, but
>>>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>>> + * General Public License for more details.
>>>> + */
>>>> +#ifndef _IIO_COUNTER_H_
>>>> +#define _IIO_COUNTER_H_
>>>> +
>>>> +#ifdef CONFIG_IIO_COUNTER
>>>> +
>>>> +#include <linux/device.h>
>>>> +#include <linux/mutex.h>
>>>> +#include <linux/types.h>
>>>> +
>>>> +#include <linux/iio/iio.h>
>>>> +
>>>> +/**
>>>> + * struct iio_counter_signal - IIO Counter Signal node
>>>> + * @id:                [DRIVER] unique ID used to identify signal
>>>> + * @name:      [DRIVER] device-specific signal name
>>>> + * @list:      [INTERN] list of all signals currently registered to counter
>>>> + */
>>>> +struct iio_counter_signal {
>>>> +       int             id;
>>>> +       const char      *name;
>>>> +
>>>> +       struct list_head        list;
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct iio_counter_trigger - IIO Counter Trigger node
>>>> + * @mode:              [DRIVER] current trigger mode state
>>>> + * @trigger_modes:     [DRIVER] available trigger modes
>>>> + * @num_trigger_modes: [DRIVER] number of modes specified in @trigger_modes
>>>> + * @signal:            [DRIVER] pointer to associated signal
>>>> + * @list:              [INTERN] list of all triggers currently registered to
>>>> + *                     value
>>>> + */
>>>> +struct iio_counter_trigger {
>>>> +       unsigned int                    mode;
>>>> +       const char *const               *trigger_modes;
>>>> +       unsigned int                    num_trigger_modes;
>>>> +       struct iio_counter_signal       *signal;
>>>> +
>>>> +       struct list_head                list;
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct iio_counter_value - IIO Counter Value node
>>>> + * @id:                        [DRIVER] unique ID used to identify value
>>>> + * @name:              [DRIVER] device-specific value name
>>>> + * @mode:              [DRIVER] current function mode state
>>>> + * @function_modes:    [DRIVER] available function modes
>>>> + * @num_function_modes:        [DRIVER] number of modes specified in @function_modes
>>>> + * @init_triggers:     [DRIVER] array of triggers for initialization
>>>> + * @num_init_triggers: [DRIVER] number of triggers specified in @init_triggers
>>>> + * @function_enum:     [INTERN] used internally to generate function attributes
>>>> + * @trigger_list_lock: [INTERN] lock for accessing @trigger_list
>>>> + * @trigger_list:      [INTERN] list of all triggers currently registered to
>>>> + *                     value
>>>> + * @list:              [INTERN] list of all values currently registered to
>>>> + *                     counter
>>>> + */
>>>> +struct iio_counter_value {
>>>> +       int                     id;
>>>> +       const char              *name;
>>>> +       unsigned int            mode;
>>>> +       const char *const       *function_modes;
>>>> +       unsigned int            num_function_modes;
>>>> +
>>>> +       struct iio_counter_trigger      *init_triggers;
>>>> +       size_t                          num_init_triggers;
>>>> +
>>>> +       struct iio_enum         function_enum;
>>>> +       struct mutex            trigger_list_lock;
>>>> +       struct list_head        trigger_list;
>>>> +
>>>> +       struct list_head        list;
>>>> +};
>>>> +
>>>> +struct iio_counter;
>>>> +
>>>> +/**
>>>> + * struct iio_counter_ops - IIO Counter related callbacks
>>>> + * @signal_read:       function to request a signal value from the device.
>>>> + *                     Return value will specify the type of value returned by
>>>> + *                     the device. val and val2 will contain the elements
>>>> + *                     making up the returned value. Note that the counter
>>>> + *                     signal_list_lock is acquired before this function is
>>>> + *                     called, and released after this function returns.
>>>> + * @signal_write:      function to write a signal value to the device.
>>>> + *                     Parameters and locking behavior are the same as
>>>> + *                     signal_read.
>>>> + * @trigger_mode_set:  function to set the trigger mode. mode is the index of
>>>> + *                     the requested mode from the value trigger_modes array.
>>>> + *                     Note that the counter value_list_lock and value
>>>> + *                     trigger_list_lock are acquired before this function is
>>>> + *                     called, and released after this function returns.
>>>> + * @trigger_mode_get:  function to get the current trigger mode. Return value
>>>> + *                     will specify the index of the current mode from the
>>>> + *                     value trigger_modes array. Locking behavior is the same
>>>> + *                     as trigger_mode_set.
>>>> + * @value_read:                function to request a value value from the device.
>>>> + *                     Return value will specify the type of value returned by
>>>> + *                     the device. val and val2 will contain the elements
>>>> + *                     making up the returned value. Note that the counter
>>>> + *                     value_list_lock is acquired before this function is
>>>> + *                     called, and released after this function returns.
>>>> + * @value_write:       function to write a value value to the device.
>>>> + *                     Parameters and locking behavior are the same as
>>>> + *                     value_read.
>>>> + * @value_function_set: function to set the value function mode. mode is the
>>>> + *                     index of the requested mode from the value
>>>> + *                     function_modes array. Note that the counter
>>>> + *                     value_list_lock is acquired before this function is
>>>> + *                     called, and released after this function returns.
>>>> + * @value_function_get: function to get the current value function mode. Return
>>>> + *                     value will specify the index of the current mode from
>>>> + *                     the value function_modes array. Locking behavior is the
>>>> + *                     same as value_function_get.
>>>> + */
>>>> +struct iio_counter_ops {
>>>> +       int (*signal_read)(struct iio_counter *counter,
>>>> +               struct iio_counter_signal *signal, int *val, int *val2);
>>>> +       int (*signal_write)(struct iio_counter *counter,
>>>> +               struct iio_counter_signal *signal, int val, int val2);
>>>> +       int (*trigger_mode_set)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value,
>>>> +               struct iio_counter_trigger *trigger, unsigned int mode);
>>>> +       int (*trigger_mode_get)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value,
>>>> +               struct iio_counter_trigger *trigger);
>>>> +       int (*value_read)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value, int *val, int *val2);
>>>> +       int (*value_write)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value, int val, int val2);
>>>> +       int (*value_function_set)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value, unsigned int mode);
>>>> +       int (*value_function_get)(struct iio_counter *counter,
>>>> +               struct iio_counter_value *value);
>>>> +};
>
>I think it would be more clear if structures iio_counter_signal,
>iio_counter_trigger
>and iio_counter_value embedded the functions related to their use.
>For example struct iio_counter_trigger could have trigger_mode_set and
>trigger_mode_get
>functions. If you do like that you can remove iio_counter_ops.

Hmm, this looks possible and would allow callbacks to be
component-specific too. However, I wonder if this would make
initialization burdensome (you would have to set every component with
their respective callbacks), and also whether component-specific
callbacks are that useful if all the components end up using the same
callback.

I will have to compare the advantages and disadvantages to each
approach.

>
>Do you think that some functions like get/set counter value, direction
>and counter
>range (min, max) are generic enough to be included in
>iio_counter_value structure ?

Yes, these are functions I believe will end up in a Counter interface at
some point as most counter devices have them in some way or another. For
this patchset however, I would like to focus on the bare necessities of
a Generic Counter. I intend to migrate these functionalities from IIO
core in future patches after the merge, where I will be able to focus on
finding an appropriate spot for them in a relevant Counter API.

>
>>>> +
>>>> +/**
>>>> + * struct iio_counter - IIO Counter data structure
>>>> + * @id:                        [DRIVER] unique ID used to identify counter
>>>> + * @name:              [DRIVER] name of the device
>>>> + * @dev:               [DRIVER] device structure, should be assigned a parent
>>>> + *                     and owner
>>>> + * @ops:               [DRIVER] callbacks from driver for counter components
>>>> + * @init_signals:      [DRIVER] array of signals for initialization
>>>> + * @num_init_signals:  [DRIVER] number of signals specified in @init_signals
>>>> + * @init_values:       [DRIVER] array of values for initialization
>>>> + * @num_init_values:   [DRIVER] number of values specified in @init_values
>>>> + * @signal_list_lock:  [INTERN] lock for accessing @signal_list
>>>> + * @signal_list:       [INTERN] list of all signals currently registered to
>>>> + *                     counter
>>>> + * @value_list_lock:   [INTERN] lock for accessing @value_list
>>>> + * @value_list:                [INTERN] list of all values currently registered to
>>>> + *                     counter
>>>> + * @channels:          [DRIVER] channel specification structure table
>>>> + * @num_channels:      [DRIVER] number of channels specified in @channels
>>>> + * @info:              [DRIVER] callbacks and constant info from driver
>>>> + * @indio_dev:         [INTERN] industrial I/O device structure
>>>> + * @driver_data:       [DRIVER] driver data
>>>> + */
>>>> +struct iio_counter {
>>>> +       int                             id;
>>>> +       const char                      *name;
>>>> +       struct device                   *dev;
>
>id, name and dev are already in struct iio_dev, maybe we can remove them ?

I originally anticipated multiple Counters associated with a single
iio_dev, however my code right now assumes a one-to-one relationship. If
it ends up staying this way, then we can remove these members since they
will likely be redundant with the indio_dev member.

>
>>>> +       const struct iio_counter_ops    *ops;
>>>> +
>>>> +       struct iio_counter_signal       *init_signals;
>>>> +       size_t                          num_init_signals;
>
>I think we can remove init_signals and num_init_signals from this structure
>because they are already linked with the values through trigger structure.

It is possible for a single Signal to be associated to multiple Values
via Triggers to each. For this reason, I believe there is value in
having an array of all the Signals together, rather than try to generate
this array by inferring the relationships between Values and their
Triggers -- although possible, building the array is more error-prone
and computationally expensive when dealing with multiple possible
mappings than simply requesting the array of all Signals is provided by
the driver.

>
>>>> +       struct iio_counter_value        *init_values;
>>>> +       size_t                          num_init_values;
>>>> +
>>>> +       struct mutex            signal_list_lock;
>>>> +       struct list_head        signal_list;
>>>> +       struct mutex            value_list_lock;
>>>> +       struct list_head        value_list;
>>>> +
>>>> +       const struct iio_chan_spec      *channels;
>>>> +       size_t                          num_channels;
>>>> +       const struct iio_info           *info;
>>>> +
>>>> +       struct iio_dev  *indio_dev;
>>>> +       void            *driver_data;
>
>"driver_data" => "priv" to do like iio_dev

I'm somewhat indifferent to the naming convention, but I do think 'priv'
may be a little too vague: a driver author may not initially realize
it's for their use and not internally modified by the system; although
'priv' does benefit by matching the iio_dev naming convention. Perhaps
Jonathan may have a suggestion.

William Breathitt Gray

>
>>>> +};
>>>> +
>>>> +int iio_counter_trigger_register(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const trigger);
>>>> +void iio_counter_trigger_unregister(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const trigger);
>>>> +int iio_counter_triggers_register(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *const triggers, const size_t num_triggers);
>>>> +void iio_counter_triggers_unregister(struct iio_counter_value *const value,
>>>> +       struct iio_counter_trigger *triggers, size_t num_triggers);
>>>> +
>>>> +int iio_counter_value_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const value);
>>>> +void iio_counter_value_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const value);
>>>> +int iio_counter_values_register(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *const values, const size_t num_values);
>>>> +void iio_counter_values_unregister(struct iio_counter *const counter,
>>>> +       struct iio_counter_value *values, size_t num_values);
>>>> +
>>>> +int iio_counter_register(struct iio_counter *const counter);
>>>> +void iio_counter_unregister(struct iio_counter *const counter);
>>>> +
>>>> +#endif /* CONFIG_IIO_COUNTER */
>>>> +
>>>> +#endif /* _IIO_COUNTER_H_ */
>>>> --
>>>> 2.14.1
>>>>
--
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Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 6f7721d1634c..24fc2dcf1995 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6577,6 +6577,13 @@  F:	Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
 F:	Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
 F:	drivers/iio/adc/envelope-detector.c
 
+IIO GENERIC COUNTER INTERFACE
+M:	William Breathitt Gray <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	drivers/iio/industrialio-counter.c
+F:	include/linux/iio/counter.h
+
 IIO MULTIPLEXER
 M:	Peter Rosin <[e-mail]>
 L:	[e-mail]
diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index b3c8c6ef0dff..78e01f4f5937 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -30,6 +30,14 @@  config IIO_CONFIGFS
 	  (e.g. software triggers). For more info see
 	  Documentation/iio/iio_configfs.txt.
 
+config IIO_COUNTER
+	bool "Enable IIO counter support"
+	help
+	  Provides IIO core support for counters. This API provides
+	  a generic interface that serves as the building blocks to
+	  create more complex counter interfaces. Rudimentary support
+	  for counters is enabled.
+
 config IIO_TRIGGER
 	bool "Enable triggered sampling support"
 	help
diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index 93c769cd99bf..6427ff38f964 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -5,6 +5,7 @@ 
 obj-$(CONFIG_IIO) += industrialio.o
 industrialio-y := industrialio-core.o industrialio-event.o inkern.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
+industrialio-$(CONFIG_IIO_COUNTER) += industrialio-counter.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
 
 obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
diff --git a/drivers/iio/counter/Kconfig b/drivers/iio/counter/Kconfig
index b37e5fc03149..3d46a790d8db 100644
--- a/drivers/iio/counter/Kconfig
+++ b/drivers/iio/counter/Kconfig
@@ -4,6 +4,7 @@ 
 # When adding new entries keep the list in alphabetical order
 
 menu "Counters"
+	depends on IIO_COUNTER
 
 config 104_QUAD_8
 	tristate "ACCES 104-QUAD-8 driver"
diff --git a/drivers/iio/industrialio-counter.c b/drivers/iio/industrialio-counter.c
new file mode 100644
index 000000000000..bdf190d010e4
--- /dev/null
+++ b/drivers/iio/industrialio-counter.c
@@ -0,0 +1,1151 @@ 
+/*
+ * Industrial I/O counter interface functions
+ * Copyright (C) 2017 William Breathitt Gray
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/types.h>
+
+#include <linux/iio/counter.h>
+
+static struct iio_counter_signal *iio_counter_signal_find_by_id(
+	const struct iio_counter *const counter, const int id)
+{
+	struct iio_counter_signal *iter;
+
+	list_for_each_entry(iter, &counter->signal_list, list)
+		if (iter->id == id)
+			return iter;
+
+	return NULL;
+}
+
+static struct iio_counter_trigger *iio_counter_trigger_find_by_id(
+	const struct iio_counter_value *const value, const int id)
+{
+	struct iio_counter_trigger *iter;
+
+	list_for_each_entry(iter, &value->trigger_list, list)
+		if (iter->signal->id == id)
+			return iter;
+
+	return NULL;
+}
+
+static struct iio_counter_value *iio_counter_value_find_by_id(
+	const struct iio_counter *const counter, const int id)
+{
+	struct iio_counter_value *iter;
+
+	list_for_each_entry(iter, &counter->value_list, list)
+		if (iter->id == id)
+			return iter;
+
+	return NULL;
+}
+
+static void iio_counter_trigger_unregister_all(
+	struct iio_counter_value *const value)
+{
+	struct iio_counter_trigger *iter, *tmp_iter;
+
+	mutex_lock(&value->trigger_list_lock);
+	list_for_each_entry_safe(iter, tmp_iter, &value->trigger_list, list)
+		list_del(&iter->list);
+	mutex_unlock(&value->trigger_list_lock);
+}
+
+static void iio_counter_signal_unregister_all(struct iio_counter *const counter)
+{
+	struct iio_counter_signal *iter, *tmp_iter;
+
+	mutex_lock(&counter->signal_list_lock);
+	list_for_each_entry_safe(iter, tmp_iter, &counter->signal_list, list)
+		list_del(&iter->list);
+	mutex_unlock(&counter->signal_list_lock);
+}
+
+static void iio_counter_value_unregister_all(struct iio_counter *const counter)
+{
+	struct iio_counter_value *iter, *tmp_iter;
+
+	mutex_lock(&counter->value_list_lock);
+	list_for_each_entry_safe(iter, tmp_iter, &counter->value_list, list) {
+		iio_counter_trigger_unregister_all(iter);
+
+		list_del(&iter->list);
+	}
+	mutex_unlock(&counter->value_list_lock);
+}
+
+static ssize_t iio_counter_signal_name_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	const struct iio_counter_signal *signal;
+
+	mutex_lock(&counter->signal_list_lock);
+	signal = iio_counter_signal_find_by_id(counter, chan->channel2);
+	mutex_unlock(&counter->signal_list_lock);
+	if (!signal)
+		return -EINVAL;
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", signal->name);
+}
+
+static ssize_t iio_counter_value_name_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	const struct iio_counter_value *value;
+
+	mutex_lock(&counter->value_list_lock);
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	mutex_unlock(&counter->value_list_lock);
+	if (!value)
+		return -EINVAL;
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", value->name);
+}
+
+static ssize_t iio_counter_value_triggers_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	const struct iio_counter_trigger *trigger;
+	ssize_t len = 0;
+
+	mutex_lock(&counter->value_list_lock);
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		len = -EINVAL;
+		goto err_find_value;
+	}
+
+	mutex_lock(&value->trigger_list_lock);
+	list_for_each_entry(trigger, &value->trigger_list, list) {
+		len += snprintf(buf + len, PAGE_SIZE - len, "%d\t%s\t%s\n",
+			trigger->signal->id, trigger->signal->name,
+			trigger->trigger_modes[trigger->mode]);
+		if (len >= PAGE_SIZE) {
+			len = -ENOMEM;
+			goto err_no_buffer_space;
+		}
+	}
+err_no_buffer_space:
+	mutex_unlock(&value->trigger_list_lock);
+
+err_find_value:
+	mutex_unlock(&counter->value_list_lock);
+
+	return len;
+}
+
+static ssize_t iio_counter_trigger_mode_read(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	ssize_t ret;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	int mode;
+
+	if (!counter->ops->trigger_mode_get)
+		return -EINVAL;
+
+	mutex_lock(&counter->value_list_lock);
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		ret = -EINVAL;
+		goto err_value;
+	}
+
+	mutex_lock(&value->trigger_list_lock);
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger) {
+		ret = -EINVAL;
+		goto err_trigger;
+	}
+
+	mode = counter->ops->trigger_mode_get(counter, value, trigger);
+
+	if (mode < 0) {
+		ret = mode;
+		goto err_trigger;
+	} else if (mode >= trigger->num_trigger_modes) {
+		ret = -EINVAL;
+		goto err_trigger;
+	}
+
+	trigger->mode = mode;
+
+	ret = scnprintf(buf, PAGE_SIZE, "%s\n", trigger->trigger_modes[mode]);
+
+	mutex_unlock(&value->trigger_list_lock);
+
+	mutex_unlock(&counter->value_list_lock);
+
+	return ret;
+
+err_trigger:
+	mutex_unlock(&value->trigger_list_lock);
+err_value:
+	mutex_unlock(&counter->value_list_lock);
+	return ret;
+}
+
+static ssize_t iio_counter_trigger_mode_write(struct iio_dev *indio_dev,
+	uintptr_t priv, const struct iio_chan_spec *chan, const char *buf,
+	size_t len)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	ssize_t err;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	unsigned int mode;
+
+	if (!counter->ops->trigger_mode_set)
+		return -EINVAL;
+
+	mutex_lock(&counter->value_list_lock);
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		err = -EINVAL;
+		goto err_value;
+	}
+
+	mutex_lock(&value->trigger_list_lock);
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger) {
+		err = -EINVAL;
+		goto err_trigger;
+	}
+
+	for (mode = 0; mode < trigger->num_trigger_modes; mode++)
+		if (sysfs_streq(buf, trigger->trigger_modes[mode]))
+			break;
+
+	if (mode >= trigger->num_trigger_modes) {
+		err = -EINVAL;
+		goto err_trigger;
+	}
+
+	err = counter->ops->trigger_mode_set(counter, value, trigger, mode);
+	if (err)
+		goto err_trigger;
+
+	trigger->mode = mode;
+
+	mutex_unlock(&value->trigger_list_lock);
+
+	mutex_unlock(&counter->value_list_lock);
+
+	return len;
+
+err_trigger:
+	mutex_unlock(&value->trigger_list_lock);
+err_value:
+	mutex_unlock(&counter->value_list_lock);
+	return err;
+}
+
+static ssize_t iio_counter_trigger_mode_available_read(
+	struct iio_dev *indio_dev, uintptr_t priv,
+	const struct iio_chan_spec *chan, char *buf)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	ssize_t len = 0;
+	struct iio_counter_trigger *trigger;
+	const int signal_id = *(int *)((void *)priv);
+	unsigned int i;
+
+	mutex_lock(&counter->value_list_lock);
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		len = -EINVAL;
+		goto err_no_value;
+	}
+
+	mutex_lock(&value->trigger_list_lock);
+
+	trigger = iio_counter_trigger_find_by_id(value, signal_id);
+	if (!trigger) {
+		len = -EINVAL;
+		goto err_no_trigger;
+	}
+
+	for (i = 0; i < trigger->num_trigger_modes; i++)
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%s ",
+			trigger->trigger_modes[i]);
+
+	mutex_unlock(&value->trigger_list_lock);
+
+	mutex_unlock(&counter->value_list_lock);
+
+	buf[len - 1] = '\n';
+
+	return len;
+
+err_no_trigger:
+	mutex_unlock(&value->trigger_list_lock);
+err_no_value:
+	mutex_unlock(&counter->value_list_lock);
+	return len;
+}
+
+static int iio_counter_value_function_set(struct iio_dev *indio_dev,
+	const struct iio_chan_spec *chan, unsigned int mode)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	int err;
+
+	if (!counter->ops->value_function_set)
+		return -EINVAL;
+
+	mutex_lock(&counter->value_list_lock);
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		err = -EINVAL;
+		goto err_value;
+	}
+
+	err = counter->ops->value_function_set(counter, value, mode);
+	if (err)
+		goto err_value;
+
+	value->mode = mode;
+
+err_value:
+	mutex_unlock(&counter->value_list_lock);
+
+	return err;
+}
+
+static int iio_counter_value_function_get(struct iio_dev *indio_dev,
+	const struct iio_chan_spec *chan)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_value *value;
+	int retval;
+
+	if (!counter->ops->value_function_get)
+		return -EINVAL;
+
+	mutex_lock(&counter->value_list_lock);
+
+	value = iio_counter_value_find_by_id(counter, chan->channel2);
+	if (!value) {
+		retval = -EINVAL;
+		goto err_value;
+	}
+
+	retval = counter->ops->value_function_get(counter, value);
+	if (retval < 0)
+		goto err_value;
+	else if (retval >= value->num_function_modes) {
+		retval = -EINVAL;
+		goto err_value;
+	}
+
+	value->mode = retval;
+
+err_value:
+	mutex_unlock(&counter->value_list_lock);
+
+	return retval;
+}
+
+static int iio_counter_value_ext_info_alloc(struct iio_chan_spec *const chan,
+	struct iio_counter_value *const value)
+{
+	const struct iio_chan_spec_ext_info ext_info_default[] = {
+		{
+			.name = "name",
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_value_name_read
+		},
+		IIO_ENUM("function", IIO_SEPARATE, &value->function_enum),
+		{
+			.name = "function_available",
+			.shared = IIO_SEPARATE,
+			.read = iio_enum_available_read,
+			.private = (void *)&value->function_enum
+		},
+		{
+			.name = "triggers",
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_value_triggers_read
+		}
+	};
+	const size_t num_default = ARRAY_SIZE(ext_info_default);
+	const struct iio_chan_spec_ext_info ext_info_trigger[] = {
+		{
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_trigger_mode_read,
+			.write = iio_counter_trigger_mode_write
+		},
+		{
+			.shared = IIO_SEPARATE,
+			.read = iio_counter_trigger_mode_available_read
+		}
+	};
+	const size_t num_ext_info_trigger = ARRAY_SIZE(ext_info_trigger);
+	const struct list_head *pos;
+	size_t num_triggers = 0;
+	size_t num_triggers_ext_info;
+	size_t num_ext_info;
+	int err;
+	struct iio_chan_spec_ext_info *ext_info;
+	const struct iio_counter_trigger *trigger_pos;
+	size_t i;
+
+	value->function_enum.items = value->function_modes;
+	value->function_enum.num_items = value->num_function_modes;
+	value->function_enum.set = iio_counter_value_function_set;
+	value->function_enum.get = iio_counter_value_function_get;
+
+	mutex_lock(&value->trigger_list_lock);
+
+	list_for_each(pos, &value->trigger_list)
+		num_triggers++;
+
+	num_triggers_ext_info = num_ext_info_trigger * num_triggers;
+	num_ext_info = num_default + num_triggers_ext_info + 1;
+
+	ext_info = kmalloc_array(num_ext_info, sizeof(*ext_info), GFP_KERNEL);
+	if (!ext_info) {
+		err = -ENOMEM;
+		goto err_ext_info_alloc;
+	}
+	ext_info[num_ext_info - 1].name = NULL;
+
+	memcpy(ext_info, ext_info_default, sizeof(ext_info_default));
+	for (i = 0; i < num_triggers_ext_info; i += num_ext_info_trigger)
+		memcpy(ext_info + num_default + i, ext_info_trigger,
+			sizeof(ext_info_trigger));
+
+	i = num_default;
+	list_for_each_entry(trigger_pos, &value->trigger_list, list) {
+		ext_info[i].name = kasprintf(GFP_KERNEL, "trigger_signal%d-%d",
+			chan->channel, trigger_pos->signal->id);
+		if (!ext_info[i].name) {
+			err = -ENOMEM;
+			goto err_name_alloc;
+		}
+		ext_info[i].private = (void *)&trigger_pos->signal->id;
+		i++;
+
+		ext_info[i].name = kasprintf(GFP_KERNEL,
+			"trigger_signal%d-%d_available",
+			chan->channel, trigger_pos->signal->id);
+		if (!ext_info[i].name) {
+			err = -ENOMEM;
+			goto err_name_alloc;
+		}
+		ext_info[i].private = (void *)&trigger_pos->signal->id;
+		i++;
+	}
+
+	chan->ext_info = ext_info;
+
+	mutex_unlock(&value->trigger_list_lock);
+
+	return 0;
+
+err_name_alloc:
+	while (i-- > num_default)
+		kfree(ext_info[i].name);
+	kfree(ext_info);
+err_ext_info_alloc:
+	mutex_unlock(&value->trigger_list_lock);
+	return err;
+}
+
+static void iio_counter_value_ext_info_free(
+	const struct iio_chan_spec *const channel)
+{
+	size_t i;
+	const char *const prefix = "trigger_signal";
+	const size_t prefix_len = strlen(prefix);
+
+	for (i = 0; channel->ext_info[i].name; i++)
+		if (!strncmp(channel->ext_info[i].name, prefix, prefix_len))
+			kfree(channel->ext_info[i].name);
+	kfree(channel->ext_info);
+}
+
+static const struct iio_chan_spec_ext_info iio_counter_signal_ext_info[] = {
+	{
+		.name = "name",
+		.shared = IIO_SEPARATE,
+		.read = iio_counter_signal_name_read
+	},
+	{}
+};
+
+static int iio_counter_channels_alloc(struct iio_counter *const counter)
+{
+	const struct list_head *pos;
+	size_t num_channels = 0;
+	int err;
+	struct iio_chan_spec *channels;
+	struct iio_counter_value *value_pos;
+	size_t i = counter->num_channels;
+	const struct iio_counter_signal *signal_pos;
+
+	mutex_lock(&counter->signal_list_lock);
+
+	list_for_each(pos, &counter->signal_list)
+		num_channels++;
+
+	if (!num_channels) {
+		err = -EINVAL;
+		goto err_no_signals;
+	}
+
+	mutex_lock(&counter->value_list_lock);
+
+	list_for_each(pos, &counter->value_list)
+		num_channels++;
+
+	num_channels += counter->num_channels;
+
+	channels = kcalloc(num_channels, sizeof(*channels), GFP_KERNEL);
+	if (!channels) {
+		err = -ENOMEM;
+		goto err_channels_alloc;
+	}
+
+	memcpy(channels, counter->channels,
+		counter->num_channels * sizeof(*counter->channels));
+
+	list_for_each_entry(value_pos, &counter->value_list, list) {
+		channels[i].type = IIO_COUNT;
+		channels[i].channel = counter->id;
+		channels[i].channel2 = value_pos->id;
+		channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+		channels[i].indexed = 1;
+		channels[i].counter = 1;
+
+		err = iio_counter_value_ext_info_alloc(channels + i, value_pos);
+		if (err)
+			goto err_value_ext_info_alloc;
+
+		i++;
+	}
+
+	mutex_unlock(&counter->value_list_lock);
+
+	list_for_each_entry(signal_pos, &counter->signal_list, list) {
+		channels[i].type = IIO_SIGNAL;
+		channels[i].channel = counter->id;
+		channels[i].channel2 = signal_pos->id;
+		channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+		channels[i].indexed = 1;
+		channels[i].counter = 1;
+		channels[i].ext_info = iio_counter_signal_ext_info;
+
+		i++;
+	}
+
+	mutex_unlock(&counter->signal_list_lock);
+
+	counter->indio_dev->num_channels = num_channels;
+	counter->indio_dev->channels = channels;
+
+	return 0;
+
+err_value_ext_info_alloc:
+	while (i-- > counter->num_channels)
+		iio_counter_value_ext_info_free(channels + i);
+	kfree(channels);
+err_channels_alloc:
+	mutex_unlock(&counter->value_list_lock);
+err_no_signals:
+	mutex_unlock(&counter->signal_list_lock);
+	return err;
+}
+
+static void iio_counter_channels_free(const struct iio_counter *const counter)
+{
+	size_t i = counter->num_channels + counter->indio_dev->num_channels;
+	const struct iio_chan_spec *const chans = counter->indio_dev->channels;
+
+	while (i-- > counter->num_channels)
+		if (chans[i].type == IIO_COUNT)
+			iio_counter_value_ext_info_free(chans + i);
+
+	kfree(chans);
+}
+
+static int iio_counter_read_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int *val, int *val2, long mask)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_signal *signal;
+	int retval;
+	struct iio_counter_value *value;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	switch (chan->type) {
+	case IIO_SIGNAL:
+		if (!counter->ops->signal_read)
+			return -EINVAL;
+
+		mutex_lock(&counter->signal_list_lock);
+		signal = iio_counter_signal_find_by_id(counter, chan->channel2);
+		if (!signal) {
+			mutex_unlock(&counter->signal_list_lock);
+			return -EINVAL;
+		}
+
+		retval = counter->ops->signal_read(counter, signal, val, val2);
+		mutex_unlock(&counter->signal_list_lock);
+
+		return retval;
+	case IIO_COUNT:
+		if (!counter->ops->value_read)
+			return -EINVAL;
+
+		mutex_lock(&counter->value_list_lock);
+		value = iio_counter_value_find_by_id(counter, chan->channel2);
+		if (!value) {
+			mutex_unlock(&counter->value_list_lock);
+			return -EINVAL;
+		}
+
+		retval = counter->ops->value_read(counter, value, val, val2);
+		mutex_unlock(&counter->value_list_lock);
+
+		return retval;
+	default:
+		if (counter->info && counter->info->read_raw)
+			return counter->info->read_raw(indio_dev, chan, val,
+				val2, mask);
+	}
+
+	return -EINVAL;
+}
+
+static int iio_counter_write_raw(struct iio_dev *indio_dev,
+	struct iio_chan_spec const *chan, int val, int val2, long mask)
+{
+	struct iio_counter *const counter = iio_priv(indio_dev);
+	struct iio_counter_signal *signal;
+	int retval;
+	struct iio_counter_value *value;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	switch (chan->type) {
+	case IIO_SIGNAL:
+		if (!counter->ops->signal_write)
+			return -EINVAL;
+
+		mutex_lock(&counter->signal_list_lock);
+		signal = iio_counter_signal_find_by_id(counter, chan->channel2);
+		if (!signal) {
+			mutex_unlock(&counter->signal_list_lock);
+			return -EINVAL;
+		}
+
+		retval = counter->ops->signal_write(counter, signal, val, val2);
+		mutex_unlock(&counter->signal_list_lock);
+
+		return retval;
+	case IIO_COUNT:
+		if (!counter->ops->value_write)
+			return -EINVAL;
+
+		mutex_lock(&counter->value_list_lock);
+		value = iio_counter_value_find_by_id(counter, chan->channel2);
+		if (!value) {
+			mutex_unlock(&counter->value_list_lock);
+			return -EINVAL;
+		}
+
+		retval = counter->ops->value_write(counter, value, val, val2);
+		mutex_unlock(&counter->value_list_lock);
+
+		return retval;
+	default:
+		if (counter->info && counter->info->write_raw)
+			return counter->info->write_raw(indio_dev, chan, val,
+				val2, mask);
+	}
+
+	return -EINVAL;
+}
+
+static int iio_counter_signal_register(struct iio_counter *const counter,
+	struct iio_counter_signal *const signal)
+{
+	int err;
+
+	if (!counter || !signal)
+		return -EINVAL;
+
+	mutex_lock(&counter->signal_list_lock);
+	if (iio_counter_signal_find_by_id(counter, signal->id)) {
+		pr_err("Duplicate counter signal ID '%d'\n", signal->id);
+		err = -EEXIST;
+		goto err_duplicate_id;
+	}
+	list_add_tail(&signal->list, &counter->signal_list);
+	mutex_unlock(&counter->signal_list_lock);
+
+	return 0;
+
+err_duplicate_id:
+	mutex_unlock(&counter->signal_list_lock);
+	return err;
+}
+
+static void iio_counter_signal_unregister(struct iio_counter *const counter,
+	struct iio_counter_signal *const signal)
+{
+	if (!counter || !signal)
+		return;
+
+	mutex_lock(&counter->signal_list_lock);
+	list_del(&signal->list);
+	mutex_unlock(&counter->signal_list_lock);
+}
+
+static int iio_counter_signals_register(struct iio_counter *const counter,
+	struct iio_counter_signal *const signals, const size_t num_signals)
+{
+	size_t i;
+	int err;
+
+	if (!counter || !signals)
+		return -EINVAL;
+
+	for (i = 0; i < num_signals; i++) {
+		err = iio_counter_signal_register(counter, signals + i);
+		if (err)
+			goto err_signal_register;
+	}
+
+	return 0;
+
+err_signal_register:
+	while (i--)
+		iio_counter_signal_unregister(counter, signals + i);
+	return err;
+}
+
+static void iio_counter_signals_unregister(struct iio_counter *const counter,
+	struct iio_counter_signal *signals, size_t num_signals)
+{
+	if (!counter || !signals)
+		return;
+
+	while (num_signals--) {
+		iio_counter_signal_unregister(counter, signals);
+		signals++;
+	}
+}
+
+/**
+ * iio_counter_trigger_register - register Trigger to Value
+ * @value: pointer to IIO Counter Value for association
+ * @trigger: pointer to IIO Counter Trigger to register
+ *
+ * The Trigger is added to the Value's trigger_list. A check is first performed
+ * to verify that the respective Signal is not already linked to the Value; if
+ * the respective Signal is already linked to the Value, the Trigger is not
+ * added to the Value's trigger_list.
+ *
+ * NOTE: This function will acquire and release the Value's trigger_list_lock
+ * during execution.
+ */
+int iio_counter_trigger_register(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const trigger)
+{
+	if (!value || !trigger || !trigger->signal)
+		return -EINVAL;
+
+	mutex_lock(&value->trigger_list_lock);
+	if (iio_counter_trigger_find_by_id(value, trigger->signal->id)) {
+		pr_err("Signal%d is already linked to counter value%d\n",
+			trigger->signal->id, value->id);
+		return -EEXIST;
+	}
+	list_add_tail(&trigger->list, &value->trigger_list);
+	mutex_unlock(&value->trigger_list_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL(iio_counter_trigger_register);
+
+/**
+ * iio_counter_trigger_unregister - unregister Trigger from Value
+ * @value: pointer to IIO Counter Value of association
+ * @trigger: pointer to IIO Counter Trigger to unregister
+ *
+ * The Trigger is removed from the Value's trigger_list.
+ *
+ * NOTE: This function will acquire and release the Value's trigger_list_lock
+ * during execution.
+ */
+void iio_counter_trigger_unregister(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const trigger)
+{
+	if (!value || !trigger || !trigger->signal)
+		return;
+
+	mutex_lock(&value->trigger_list_lock);
+	list_del(&trigger->list);
+	mutex_unlock(&value->trigger_list_lock);
+}
+EXPORT_SYMBOL(iio_counter_trigger_unregister);
+
+/**
+ * iio_counter_triggers_register - register an array of Triggers to Value
+ * @value: pointer to IIO Counter Value for association
+ * @triggers: array of pointers to IIO Counter Triggers to register
+ *
+ * The iio_counter_trigger_register function is called for each Trigger in the
+ * array. The @triggers array is traversed for the first @num_triggers Triggers.
+ *
+ * NOTE: @num_triggers must not be greater than the size of the @triggers array.
+ */
+int iio_counter_triggers_register(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const triggers, const size_t num_triggers)
+{
+	size_t i;
+	int err;
+
+	if (!value || !triggers)
+		return -EINVAL;
+
+	for (i = 0; i < num_triggers; i++) {
+		err = iio_counter_trigger_register(value, triggers + i);
+		if (err)
+			goto err_trigger_register;
+	}
+
+	return 0;
+
+err_trigger_register:
+	while (i--)
+		iio_counter_trigger_unregister(value, triggers + i);
+	return err;
+}
+EXPORT_SYMBOL(iio_counter_triggers_register);
+
+/**
+ * iio_counter_triggers_unregister - unregister Triggers from Value
+ * @value: pointer to IIO Counter Value of association
+ * @triggers: array of pointers to IIO Counter Triggers to unregister
+ *
+ * The iio_counter_trigger_unregister function is called for each Trigger in the
+ * array. The @triggers array is traversed for the first @num_triggers Triggers.
+ *
+ * NOTE: @num_triggers must not be greater than the size of the @triggers array.
+ */
+void iio_counter_triggers_unregister(struct iio_counter_value *const value,
+	struct iio_counter_trigger *triggers, size_t num_triggers)
+{
+	if (!value || !triggers)
+		return;
+
+	while (num_triggers--) {
+		iio_counter_trigger_unregister(value, triggers);
+		triggers++;
+	}
+}
+EXPORT_SYMBOL(iio_counter_triggers_unregister);
+
+/**
+ * iio_counter_value_register - register Value to Counter
+ * @counter: pointer to IIO Counter for association
+ * @value: pointer to IIO Counter Value to register
+ *
+ * The registration process occurs in two major steps. First, the Value is
+ * initialized: trigger_list_lock is initialized, trigger_list is initialized,
+ * and init_triggers if not NULL is passed to iio_counter_triggers_register.
+ * Second, the Value is added to the Counter's value_list. A check is first
+ * performed to verify that the Value is not already associated to the Counter
+ * (via the Value's unique ID); if the Value is already associated to the
+ * Counter, the Value is not added to the Counter's value_list and all of the
+ * Value's Triggers are unregistered.
+ *
+ * NOTE: This function will acquire and release the Counter's value_list_lock
+ * during execution.
+ */
+int iio_counter_value_register(struct iio_counter *const counter,
+	struct iio_counter_value *const value)
+{
+	int err;
+
+	if (!counter || !value)
+		return -EINVAL;
+
+	mutex_init(&value->trigger_list_lock);
+	INIT_LIST_HEAD(&value->trigger_list);
+
+	if (value->init_triggers) {
+		err = iio_counter_triggers_register(value,
+			value->init_triggers, value->num_init_triggers);
+		if (err)
+			return err;
+	}
+
+	mutex_lock(&counter->value_list_lock);
+	if (iio_counter_value_find_by_id(counter, value->id)) {
+		pr_err("Duplicate counter value ID '%d'\n", value->id);
+		err = -EEXIST;
+		goto err_duplicate_id;
+	}
+	list_add_tail(&value->list, &counter->value_list);
+	mutex_unlock(&counter->value_list_lock);
+
+	return 0;
+
+err_duplicate_id:
+	mutex_unlock(&counter->value_list_lock);
+	iio_counter_trigger_unregister_all(value);
+	return err;
+}
+EXPORT_SYMBOL(iio_counter_value_register);
+
+/**
+ * iio_counter_value_unregister - unregister Value from Counter
+ * @counter: pointer to IIO Counter of association
+ * @value: pointer to IIO Counter Value to unregister
+ *
+ * The Value is removed from the Counter's value_list and all of the Value's
+ * Triggers are unregistered.
+ *
+ * NOTE: This function will acquire and release the Counter's value_list_lock
+ * during execution.
+ */
+void iio_counter_value_unregister(struct iio_counter *const counter,
+	struct iio_counter_value *const value)
+{
+	if (!counter || !value)
+		return;
+
+	mutex_lock(&counter->value_list_lock);
+	list_del(&value->list);
+	mutex_unlock(&counter->value_list_lock);
+
+	iio_counter_trigger_unregister_all(value);
+}
+EXPORT_SYMBOL(iio_counter_value_unregister);
+
+/**
+ * iio_counter_values_register - register an array of Values to Counter
+ * @counter: pointer to IIO Counter for association
+ * @values: array of pointers to IIO Counter Values to register
+ *
+ * The iio_counter_value_register function is called for each Value in the
+ * array. The @values array is traversed for the first @num_values Values.
+ *
+ * NOTE: @num_values must not be greater than the size of the @values array.
+ */
+int iio_counter_values_register(struct iio_counter *const counter,
+	struct iio_counter_value *const values, const size_t num_values)
+{
+	size_t i;
+	int err;
+
+	if (!counter || !values)
+		return -EINVAL;
+
+	for (i = 0; i < num_values; i++) {
+		err = iio_counter_value_register(counter, values + i);
+		if (err)
+			goto err_values_register;
+	}
+
+	return 0;
+
+err_values_register:
+	while (i--)
+		iio_counter_value_unregister(counter, values + i);
+	return err;
+}
+EXPORT_SYMBOL(iio_counter_values_register);
+
+/**
+ * iio_counter_values_unregister - unregister Values from Counter
+ * @counter: pointer to IIO Counter of association
+ * @values: array of pointers to IIO Counter Values to unregister
+ *
+ * The iio_counter_value_unregister function is called for each Value in the
+ * array. The @values array is traversed for the first @num_values Values.
+ *
+ * NOTE: @num_values must not be greater than the size of the @values array.
+ */
+void iio_counter_values_unregister(struct iio_counter *const counter,
+	struct iio_counter_value *values, size_t num_values)
+{
+	if (!counter || !values)
+		return;
+
+	while (num_values--) {
+		iio_counter_value_unregister(counter, values);
+		values++;
+	}
+}
+EXPORT_SYMBOL(iio_counter_values_unregister);
+
+/**
+ * iio_counter_register - register Counter to the system
+ * @counter: pointer to IIO Counter to register
+ *
+ * This function piggybacks off of iio_device_register. First, the relevant
+ * Counter members are initialized; if init_signals is not NULL it is passed to
+ * iio_counter_signals_register, and similarly if init_values is not NULL it is
+ * passed to iio_counter_values_register. Next, a struct iio_dev is allocated by
+ * a call to iio_device_alloc and initialized for the Counter, IIO channels are
+ * allocated, the Counter is copied as the private data, and finally
+ * iio_device_register is called.
+ */
+int iio_counter_register(struct iio_counter *const counter)
+{
+	const struct iio_info info_default = {
+		.read_raw = iio_counter_read_raw,
+		.write_raw = iio_counter_write_raw
+	};
+	int err;
+	struct iio_info *info;
+	struct iio_counter *priv;
+
+	if (!counter)
+		return -EINVAL;
+
+	mutex_init(&counter->signal_list_lock);
+	INIT_LIST_HEAD(&counter->signal_list);
+
+	if (counter->init_signals) {
+		err = iio_counter_signals_register(counter,
+			counter->init_signals, counter->num_init_signals);
+		if (err)
+			return err;
+	}
+
+	mutex_init(&counter->value_list_lock);
+	INIT_LIST_HEAD(&counter->value_list);
+
+	if (counter->init_values) {
+		err = iio_counter_values_register(counter,
+			counter->init_values, counter->num_init_values);
+		if (err)
+			goto err_values_register;
+	}
+
+	counter->indio_dev = iio_device_alloc(sizeof(*counter));
+	if (!counter->indio_dev) {
+		err = -ENOMEM;
+		goto err_iio_device_alloc;
+	}
+
+	info = kmalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		err = -ENOMEM;
+		goto err_info_alloc;
+	}
+	if (counter->info) {
+		memcpy(info, counter->info, sizeof(*counter->info));
+		info->read_raw = iio_counter_read_raw;
+		info->write_raw = iio_counter_write_raw;
+	} else {
+		memcpy(info, &info_default, sizeof(info_default));
+	}
+
+	counter->indio_dev->info = info;
+	counter->indio_dev->modes = INDIO_DIRECT_MODE;
+	counter->indio_dev->name = counter->name;
+	counter->indio_dev->dev.parent = counter->dev;
+
+	err = iio_counter_channels_alloc(counter);
+	if (err)
+		goto err_channels_alloc;
+
+	priv = iio_priv(counter->indio_dev);
+	memcpy(priv, counter, sizeof(*priv));
+
+	err = iio_device_register(priv->indio_dev);
+	if (err)
+		goto err_iio_device_register;
+
+	return 0;
+
+err_iio_device_register:
+	iio_counter_channels_free(counter);
+err_channels_alloc:
+	kfree(info);
+err_info_alloc:
+	iio_device_free(counter->indio_dev);
+err_iio_device_alloc:
+	iio_counter_values_unregister(counter, counter->init_values,
+		counter->num_init_values);
+err_values_register:
+	iio_counter_signals_unregister(counter, counter->init_signals,
+		counter->num_init_signals);
+	return err;
+}
+EXPORT_SYMBOL(iio_counter_register);
+
+/**
+ * iio_counter_unregister - unregister Counter from the system
+ * @counter: pointer to IIO Counter to unregister
+ *
+ * The Counter is unregistered from the system. The indio_dev is unregistered,
+ * allocated memory is freed, and all associated Values and Signals are
+ * unregistered.
+ */
+void iio_counter_unregister(struct iio_counter *const counter)
+{
+	const struct iio_info *const info = counter->indio_dev->info;
+
+	if (!counter)
+		return;
+
+	iio_device_unregister(counter->indio_dev);
+
+	iio_counter_channels_free(counter);
+
+	kfree(info);
+	iio_device_free(counter->indio_dev);
+
+	iio_counter_value_unregister_all(counter);
+	iio_counter_signal_unregister_all(counter);
+}
+EXPORT_SYMBOL(iio_counter_unregister);
diff --git a/include/linux/iio/counter.h b/include/linux/iio/counter.h
new file mode 100644
index 000000000000..1c1ca13a6053
--- /dev/null
+++ b/include/linux/iio/counter.h
@@ -0,0 +1,221 @@ 
+/*
+ * Industrial I/O counter interface
+ * Copyright (C) 2017 William Breathitt Gray
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#ifndef _IIO_COUNTER_H_
+#define _IIO_COUNTER_H_
+
+#ifdef CONFIG_IIO_COUNTER
+
+#include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#include <linux/iio/iio.h>
+
+/**
+ * struct iio_counter_signal - IIO Counter Signal node
+ * @id:		[DRIVER] unique ID used to identify signal
+ * @name:	[DRIVER] device-specific signal name
+ * @list:	[INTERN] list of all signals currently registered to counter
+ */
+struct iio_counter_signal {
+	int		id;
+	const char	*name;
+
+	struct list_head	list;
+};
+
+/**
+ * struct iio_counter_trigger - IIO Counter Trigger node
+ * @mode:		[DRIVER] current trigger mode state
+ * @trigger_modes:	[DRIVER] available trigger modes
+ * @num_trigger_modes:	[DRIVER] number of modes specified in @trigger_modes
+ * @signal:		[DRIVER] pointer to associated signal
+ * @list:		[INTERN] list of all triggers currently registered to
+ *			value
+ */
+struct iio_counter_trigger {
+	unsigned int			mode;
+	const char *const		*trigger_modes;
+	unsigned int			num_trigger_modes;
+	struct iio_counter_signal	*signal;
+
+	struct list_head		list;
+};
+
+/**
+ * struct iio_counter_value - IIO Counter Value node
+ * @id:			[DRIVER] unique ID used to identify value
+ * @name:		[DRIVER] device-specific value name
+ * @mode:		[DRIVER] current function mode state
+ * @function_modes:	[DRIVER] available function modes
+ * @num_function_modes:	[DRIVER] number of modes specified in @function_modes
+ * @init_triggers:	[DRIVER] array of triggers for initialization
+ * @num_init_triggers:	[DRIVER] number of triggers specified in @init_triggers
+ * @function_enum:	[INTERN] used internally to generate function attributes
+ * @trigger_list_lock:	[INTERN] lock for accessing @trigger_list
+ * @trigger_list:	[INTERN] list of all triggers currently registered to
+ *			value
+ * @list:		[INTERN] list of all values currently registered to
+ *			counter
+ */
+struct iio_counter_value {
+	int			id;
+	const char		*name;
+	unsigned int		mode;
+	const char *const	*function_modes;
+	unsigned int		num_function_modes;
+
+	struct iio_counter_trigger	*init_triggers;
+	size_t				num_init_triggers;
+
+	struct iio_enum		function_enum;
+	struct mutex		trigger_list_lock;
+	struct list_head	trigger_list;
+
+	struct list_head	list;
+};
+
+struct iio_counter;
+
+/**
+ * struct iio_counter_ops - IIO Counter related callbacks
+ * @signal_read:	function to request a signal value from the device.
+ *			Return value will specify the type of value returned by
+ *			the device. val and val2 will contain the elements
+ *			making up the returned value. Note that the counter
+ *			signal_list_lock is acquired before this function is
+ *			called, and released after this function returns.
+ * @signal_write:	function to write a signal value to the device.
+ *			Parameters and locking behavior are the same as
+ *			signal_read.
+ * @trigger_mode_set:	function to set the trigger mode. mode is the index of
+ *			the requested mode from the value trigger_modes array.
+ *			Note that the counter value_list_lock and value
+ *			trigger_list_lock are acquired before this function is
+ *			called, and released after this function returns.
+ * @trigger_mode_get:	function to get the current trigger mode. Return value
+ *			will specify the index of the current mode from the
+ *			value trigger_modes array. Locking behavior is the same
+ *			as trigger_mode_set.
+ * @value_read:		function to request a value value from the device.
+ *			Return value will specify the type of value returned by
+ *			the device. val and val2 will contain the elements
+ *			making up the returned value. Note that the counter
+ *			value_list_lock is acquired before this function is
+ *			called, and released after this function returns.
+ * @value_write:	function to write a value value to the device.
+ *			Parameters and locking behavior are the same as
+ *			value_read.
+ * @value_function_set: function to set the value function mode. mode is the
+ *			index of the requested mode from the value
+ *			function_modes array. Note that the counter
+ *			value_list_lock is acquired before this function is
+ *			called, and released after this function returns.
+ * @value_function_get: function to get the current value function mode. Return
+ *			value will specify the index of the current mode from
+ *			the value function_modes array. Locking behavior is the
+ *			same as value_function_get.
+ */
+struct iio_counter_ops {
+	int (*signal_read)(struct iio_counter *counter,
+		struct iio_counter_signal *signal, int *val, int *val2);
+	int (*signal_write)(struct iio_counter *counter,
+		struct iio_counter_signal *signal, int val, int val2);
+	int (*trigger_mode_set)(struct iio_counter *counter,
+		struct iio_counter_value *value,
+		struct iio_counter_trigger *trigger, unsigned int mode);
+	int (*trigger_mode_get)(struct iio_counter *counter,
+		struct iio_counter_value *value,
+		struct iio_counter_trigger *trigger);
+	int (*value_read)(struct iio_counter *counter,
+		struct iio_counter_value *value, int *val, int *val2);
+	int (*value_write)(struct iio_counter *counter,
+		struct iio_counter_value *value, int val, int val2);
+	int (*value_function_set)(struct iio_counter *counter,
+		struct iio_counter_value *value, unsigned int mode);
+	int (*value_function_get)(struct iio_counter *counter,
+		struct iio_counter_value *value);
+};
+
+/**
+ * struct iio_counter - IIO Counter data structure
+ * @id:			[DRIVER] unique ID used to identify counter
+ * @name:		[DRIVER] name of the device
+ * @dev:		[DRIVER] device structure, should be assigned a parent
+ *			and owner
+ * @ops:		[DRIVER] callbacks from driver for counter components
+ * @init_signals:	[DRIVER] array of signals for initialization
+ * @num_init_signals:	[DRIVER] number of signals specified in @init_signals
+ * @init_values:	[DRIVER] array of values for initialization
+ * @num_init_values:	[DRIVER] number of values specified in @init_values
+ * @signal_list_lock:	[INTERN] lock for accessing @signal_list
+ * @signal_list:	[INTERN] list of all signals currently registered to
+ *			counter
+ * @value_list_lock:	[INTERN] lock for accessing @value_list
+ * @value_list:		[INTERN] list of all values currently registered to
+ *			counter
+ * @channels:		[DRIVER] channel specification structure table
+ * @num_channels:	[DRIVER] number of channels specified in @channels
+ * @info:		[DRIVER] callbacks and constant info from driver
+ * @indio_dev:		[INTERN] industrial I/O device structure
+ * @driver_data:	[DRIVER] driver data
+ */
+struct iio_counter {
+	int				id;
+	const char			*name;
+	struct device			*dev;
+	const struct iio_counter_ops	*ops;
+
+	struct iio_counter_signal	*init_signals;
+	size_t				num_init_signals;
+	struct iio_counter_value	*init_values;
+	size_t				num_init_values;
+
+	struct mutex		signal_list_lock;
+	struct list_head	signal_list;
+	struct mutex		value_list_lock;
+	struct list_head	value_list;
+
+	const struct iio_chan_spec	*channels;
+	size_t				num_channels;
+	const struct iio_info		*info;
+
+	struct iio_dev	*indio_dev;
+	void		*driver_data;
+};
+
+int iio_counter_trigger_register(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const trigger);
+void iio_counter_trigger_unregister(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const trigger);
+int iio_counter_triggers_register(struct iio_counter_value *const value,
+	struct iio_counter_trigger *const triggers, const size_t num_triggers);
+void iio_counter_triggers_unregister(struct iio_counter_value *const value,
+	struct iio_counter_trigger *triggers, size_t num_triggers);
+
+int iio_counter_value_register(struct iio_counter *const counter,
+	struct iio_counter_value *const value);
+void iio_counter_value_unregister(struct iio_counter *const counter,
+	struct iio_counter_value *const value);
+int iio_counter_values_register(struct iio_counter *const counter,
+	struct iio_counter_value *const values, const size_t num_values);
+void iio_counter_values_unregister(struct iio_counter *const counter,
+	struct iio_counter_value *values, size_t num_values);
+
+int iio_counter_register(struct iio_counter *const counter);
+void iio_counter_unregister(struct iio_counter *const counter);
+
+#endif /* CONFIG_IIO_COUNTER */
+
+#endif /* _IIO_COUNTER_H_ */