diff mbox

[RFC,v2,3/6] serdev: add multiplexer support

Message ID 1500305076-15570-4-git-send-email-ulrich.hecht+renesas@gmail.com (mailing list archive)
State RFC
Delegated to: Geert Uytterhoeven
Headers show

Commit Message

Ulrich Hecht July 17, 2017, 3:24 p.m. UTC 
Adds an interface for slave device multiplexing using the mux subsystem.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
---
 drivers/tty/serdev/Kconfig  |  3 +++
 drivers/tty/serdev/Makefile |  1 +
 drivers/tty/serdev/core.c   | 14 +++++++++-
 drivers/tty/serdev/mux.c    | 66 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/serdev.h      | 16 ++++++++---
 5 files changed, 96 insertions(+), 4 deletions(-)
 create mode 100644 drivers/tty/serdev/mux.c

Comments

Rob Herring (Arm) July 18, 2017, 11:06 p.m. UTC | #1 
On Mon, Jul 17, 2017 at 10:24 AM, Ulrich Hecht
<ulrich.hecht+renesas@gmail.com> wrote:
> Adds an interface for slave device multiplexing using the mux subsystem.
>
> Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
> ---
>  drivers/tty/serdev/Kconfig  |  3 +++
>  drivers/tty/serdev/Makefile |  1 +
>  drivers/tty/serdev/core.c   | 14 +++++++++-
>  drivers/tty/serdev/mux.c    | 66 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/serdev.h      | 16 ++++++++---
>  5 files changed, 96 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/tty/serdev/mux.c
>
> diff --git a/drivers/tty/serdev/Kconfig b/drivers/tty/serdev/Kconfig
> index cdc6b82..9096b71 100644
> --- a/drivers/tty/serdev/Kconfig
> +++ b/drivers/tty/serdev/Kconfig
> @@ -13,4 +13,7 @@ config SERIAL_DEV_CTRL_TTYPORT
>         depends on TTY
>         depends on SERIAL_DEV_BUS != m
>
> +config SERIAL_DEV_MUX
> +       bool "Serial device multiplexer support"

I think this breaks for modules.

I'm inclined to just keep mux support in the core.

> +
>  endif
> diff --git a/drivers/tty/serdev/Makefile b/drivers/tty/serdev/Makefile
> index 0cbdb94..d713381 100644
> --- a/drivers/tty/serdev/Makefile
> +++ b/drivers/tty/serdev/Makefile
> @@ -1,5 +1,6 @@
>  serdev-objs := core.o
>
>  obj-$(CONFIG_SERIAL_DEV_BUS) += serdev.o
> +obj-$(CONFIG_SERIAL_DEV_MUX) += mux.o
>
>  obj-$(CONFIG_SERIAL_DEV_CTRL_TTYPORT) += serdev-ttyport.o
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index 1fbaa4c..92c5bfa 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -305,7 +305,8 @@ struct serdev_device *serdev_device_alloc(struct serdev_controller *ctrl)
>                 return NULL;
>
>         serdev->ctrl = ctrl;
> -       ctrl->serdev = serdev;
> +       if (!ctrl->serdev)
> +               ctrl->serdev = serdev;
>         device_initialize(&serdev->dev);
>         serdev->dev.parent = &ctrl->dev;
>         serdev->dev.bus = &serdev_bus_type;
> @@ -368,6 +369,8 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
>         struct serdev_device *serdev = NULL;
>         int err;
>         bool found = false;
> +       int nr = 0;
> +       u32 reg;
>
>         for_each_available_child_of_node(ctrl->dev.of_node, node) {
>                 if (!of_get_property(node, "compatible", NULL))
> @@ -380,6 +383,10 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
>                         continue;
>
>                 serdev->dev.of_node = node;
> +               serdev->nr = nr++;
> +
> +               if (!of_property_read_u32(node, "reg", &reg))
> +                       serdev->mux_addr = reg;

Perhaps nr should just be assigned reg value.

>
>                 err = serdev_device_add(serdev);
>                 if (err) {
> @@ -414,6 +421,11 @@ int serdev_controller_add(struct serdev_controller *ctrl)
>         if (ret)
>                 return ret;
>
> +#ifdef CONFIG_SERIAL_DEV_MUX
> +       if (of_serdev_register_mux(ctrl) == -EPROBE_DEFER)
> +               return -EPROBE_DEFER;
> +#endif
> +
>         ret = of_serdev_register_devices(ctrl);
>         if (ret)
>                 goto out_dev_del;
> diff --git a/drivers/tty/serdev/mux.c b/drivers/tty/serdev/mux.c
> new file mode 100644
> index 0000000..fc9405b
> --- /dev/null
> +++ b/drivers/tty/serdev/mux.c
> @@ -0,0 +1,66 @@
> +/*
> + * Copyright (C) 2017 Ulrich Hecht
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 and
> + * only 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/mux/consumer.h>
> +#include <linux/mux/driver.h>
> +#include <linux/of_gpio.h>
> +#include <linux/serdev.h>
> +#include <linux/slab.h>
> +
> +int serdev_device_mux_select(struct serdev_device *serdev)
> +{
> +       struct mux_control *mux = serdev->ctrl->mux;
> +       int ret;
> +
> +       if (!mux)
> +               return -EINVAL;
> +
> +       ret = mux_control_select(mux, serdev->mux_addr);
> +       serdev->ctrl->mux_do_not_deselect = ret < 0;
> +
> +       serdev->ctrl->serdev = serdev;
> +
> +       return ret;
> +}
> +
> +int serdev_device_mux_deselect(struct serdev_device *serdev)
> +{
> +       struct mux_control *mux = serdev->ctrl->mux;
> +
> +       if (!mux)
> +               return -EINVAL;
> +
> +       if (!serdev->ctrl->mux_do_not_deselect)
> +               return mux_control_deselect(mux);
> +       else
> +               return 0;
> +}
> +
> +int of_serdev_register_mux(struct serdev_controller *ctrl)
> +{
> +       struct mux_control *mux;
> +       struct device *dev = &ctrl->dev;
> +
> +       mux = devm_mux_control_get(dev, NULL);
> +
> +       if (IS_ERR(mux)) {
> +               if (PTR_ERR(mux) != -EPROBE_DEFER)
> +                       dev_err(dev, "failed to get control mux\n");
> +               return PTR_ERR(mux);
> +       }
> +
> +       ctrl->mux = mux;
> +
> +       return 0;
> +}
> +
> diff --git a/include/linux/serdev.h b/include/linux/serdev.h
> index 8b67fcd..26d5994 100644
> --- a/include/linux/serdev.h
> +++ b/include/linux/serdev.h
> @@ -17,6 +17,7 @@
>  #include <linux/device.h>
>  #include <linux/termios.h>
>  #include <linux/delay.h>
> +#include <linux/rtmutex.h>
>
>  struct serdev_controller;
>  struct serdev_device;
> @@ -51,6 +52,7 @@ struct serdev_device {
>         const struct serdev_device_ops *ops;
>         struct completion write_comp;
>         struct mutex write_lock;
> +       int mux_addr;
>  };
>
>  static inline struct serdev_device *to_serdev_device(struct device *d)
> @@ -76,6 +78,8 @@ static inline struct serdev_device_driver *to_serdev_device_driver(struct device
>         return container_of(d, struct serdev_device_driver, driver);
>  }
>
> +int of_serdev_register_mux(struct serdev_controller *ctrl);
> +
>  /*
>   * serdev controller structures
>   */
> @@ -97,14 +101,18 @@ struct serdev_controller_ops {
>   * struct serdev_controller - interface to the serdev controller
>   * @dev:       Driver model representation of the device.
>   * @nr:                number identifier for this controller/bus.
> - * @serdev:    Pointer to slave device for this controller.
> + * @serdev:    Pointer to active slave device for this controller.
>   * @ops:       Controller operations.
> + * @mux:       Slave multiplexer control.
> + * @mux_do_not_deselect: Set if slave selection failed.
>   */
>  struct serdev_controller {
>         struct device           dev;
>         unsigned int            nr;
>         struct serdev_device    *serdev;
>         const struct serdev_controller_ops *ops;
> +       struct mux_control      *mux;
> +       int                     mux_do_not_deselect;
>  };
>
>  static inline struct serdev_controller *to_serdev_controller(struct device *d)
> @@ -172,7 +180,7 @@ static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl
>  {
>         struct serdev_device *serdev = ctrl->serdev;
>
> -       if (!serdev || !serdev->ops->write_wakeup)
> +       if (!serdev || !serdev->ops || !serdev->ops->write_wakeup)

When is ops ever NULL? Should be a separate change AFIACT.

>                 return;
>
>         serdev->ops->write_wakeup(serdev);
> @@ -184,7 +192,7 @@ static inline int serdev_controller_receive_buf(struct serdev_controller *ctrl,
>  {
>         struct serdev_device *serdev = ctrl->serdev;
>
> -       if (!serdev || !serdev->ops->receive_buf)
> +       if (!serdev || !serdev->ops || !serdev->ops->receive_buf)
>                 return -EINVAL;
>
>         return serdev->ops->receive_buf(serdev, data, count);
> @@ -204,6 +212,8 @@ void serdev_device_write_wakeup(struct serdev_device *);
>  int serdev_device_write(struct serdev_device *, const unsigned char *, size_t, unsigned long);
>  void serdev_device_write_flush(struct serdev_device *);
>  int serdev_device_write_room(struct serdev_device *);
> +int serdev_device_mux_select(struct serdev_device *);
> +int serdev_device_mux_deselect(struct serdev_device *);
>
>  /*
>   * serdev device driver functions
> --
> 2.7.4
>
Peter Rosin July 19, 2017, 7:22 a.m. UTC | #2 
On 2017-07-17 17:24, Ulrich Hecht wrote:
> Adds an interface for slave device multiplexing using the mux subsystem.
> 
> Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
> ---
>  drivers/tty/serdev/Kconfig  |  3 +++
>  drivers/tty/serdev/Makefile |  1 +
>  drivers/tty/serdev/core.c   | 14 +++++++++-
>  drivers/tty/serdev/mux.c    | 66 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/serdev.h      | 16 ++++++++---
>  5 files changed, 96 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/tty/serdev/mux.c
> 
> diff --git a/drivers/tty/serdev/Kconfig b/drivers/tty/serdev/Kconfig
> index cdc6b82..9096b71 100644
> --- a/drivers/tty/serdev/Kconfig
> +++ b/drivers/tty/serdev/Kconfig
> @@ -13,4 +13,7 @@ config SERIAL_DEV_CTRL_TTYPORT
>  	depends on TTY
>  	depends on SERIAL_DEV_BUS != m
>  
> +config SERIAL_DEV_MUX
> +	bool "Serial device multiplexer support"

Here, you should

	select MULTIPLEXER

And, instead of adding a config option, you might want to consider
making the mux optional instead. See

https://lkml.org/lkml/2017/7/14/655

> +
>  endif
> diff --git a/drivers/tty/serdev/Makefile b/drivers/tty/serdev/Makefile
> index 0cbdb94..d713381 100644
> --- a/drivers/tty/serdev/Makefile
> +++ b/drivers/tty/serdev/Makefile
> @@ -1,5 +1,6 @@
>  serdev-objs := core.o
>  
>  obj-$(CONFIG_SERIAL_DEV_BUS) += serdev.o
> +obj-$(CONFIG_SERIAL_DEV_MUX) += mux.o
>  
>  obj-$(CONFIG_SERIAL_DEV_CTRL_TTYPORT) += serdev-ttyport.o
> diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> index 1fbaa4c..92c5bfa 100644
> --- a/drivers/tty/serdev/core.c
> +++ b/drivers/tty/serdev/core.c
> @@ -305,7 +305,8 @@ struct serdev_device *serdev_device_alloc(struct serdev_controller *ctrl)
>  		return NULL;
>  
>  	serdev->ctrl = ctrl;
> -	ctrl->serdev = serdev;
> +	if (!ctrl->serdev)
> +		ctrl->serdev = serdev;
>  	device_initialize(&serdev->dev);
>  	serdev->dev.parent = &ctrl->dev;
>  	serdev->dev.bus = &serdev_bus_type;
> @@ -368,6 +369,8 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
>  	struct serdev_device *serdev = NULL;
>  	int err;
>  	bool found = false;
> +	int nr = 0;
> +	u32 reg;
>  
>  	for_each_available_child_of_node(ctrl->dev.of_node, node) {
>  		if (!of_get_property(node, "compatible", NULL))
> @@ -380,6 +383,10 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
>  			continue;
>  
>  		serdev->dev.of_node = node;
> +		serdev->nr = nr++;
> +
> +		if (!of_property_read_u32(node, "reg", &reg))
> +			serdev->mux_addr = reg;
>  
>  		err = serdev_device_add(serdev);
>  		if (err) {
> @@ -414,6 +421,11 @@ int serdev_controller_add(struct serdev_controller *ctrl)
>  	if (ret)
>  		return ret;
>  
> +#ifdef CONFIG_SERIAL_DEV_MUX
> +	if (of_serdev_register_mux(ctrl) == -EPROBE_DEFER)
> +		return -EPROBE_DEFER;
> +#endif
> +
>  	ret = of_serdev_register_devices(ctrl);
>  	if (ret)
>  		goto out_dev_del;
> diff --git a/drivers/tty/serdev/mux.c b/drivers/tty/serdev/mux.c
> new file mode 100644
> index 0000000..fc9405b
> --- /dev/null
> +++ b/drivers/tty/serdev/mux.c
> @@ -0,0 +1,66 @@
> +/*
> + * Copyright (C) 2017 Ulrich Hecht
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 and
> + * only 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/mux/consumer.h>
> +#include <linux/mux/driver.h>
> +#include <linux/of_gpio.h>
> +#include <linux/serdev.h>
> +#include <linux/slab.h>
> +
> +int serdev_device_mux_select(struct serdev_device *serdev)
> +{
> +	struct mux_control *mux = serdev->ctrl->mux;
> +	int ret;
> +
> +	if (!mux)
> +		return -EINVAL;
> +
> +	ret = mux_control_select(mux, serdev->mux_addr);
> +	serdev->ctrl->mux_do_not_deselect = ret < 0;
> +
> +	serdev->ctrl->serdev = serdev;
> +
> +	return ret;
> +}
> +
> +int serdev_device_mux_deselect(struct serdev_device *serdev)
> +{
> +	struct mux_control *mux = serdev->ctrl->mux;
> +
> +	if (!mux)
> +		return -EINVAL;
> +
> +	if (!serdev->ctrl->mux_do_not_deselect)
> +		return mux_control_deselect(mux);
> +	else
> +		return 0;
> +}
> +
> +int of_serdev_register_mux(struct serdev_controller *ctrl)
> +{
> +	struct mux_control *mux;
> +	struct device *dev = &ctrl->dev;
> +
> +	mux = devm_mux_control_get(dev, NULL);
> +
> +	if (IS_ERR(mux)) {
> +		if (PTR_ERR(mux) != -EPROBE_DEFER)
> +			dev_err(dev, "failed to get control mux\n");
> +		return PTR_ERR(mux);
> +	}
> +
> +	ctrl->mux = mux;
> +
> +	return 0;
> +}
> +
> diff --git a/include/linux/serdev.h b/include/linux/serdev.h
> index 8b67fcd..26d5994 100644
> --- a/include/linux/serdev.h
> +++ b/include/linux/serdev.h
> @@ -17,6 +17,7 @@
>  #include <linux/device.h>
>  #include <linux/termios.h>
>  #include <linux/delay.h>
> +#include <linux/rtmutex.h>
>  
>  struct serdev_controller;
>  struct serdev_device;
> @@ -51,6 +52,7 @@ struct serdev_device {
>  	const struct serdev_device_ops *ops;
>  	struct completion write_comp;
>  	struct mutex write_lock;
> +	int mux_addr;
>  };
>  
>  static inline struct serdev_device *to_serdev_device(struct device *d)
> @@ -76,6 +78,8 @@ static inline struct serdev_device_driver *to_serdev_device_driver(struct device
>  	return container_of(d, struct serdev_device_driver, driver);
>  }
>  
> +int of_serdev_register_mux(struct serdev_controller *ctrl);
> +
>  /*
>   * serdev controller structures
>   */
> @@ -97,14 +101,18 @@ struct serdev_controller_ops {
>   * struct serdev_controller - interface to the serdev controller
>   * @dev:	Driver model representation of the device.
>   * @nr:		number identifier for this controller/bus.
> - * @serdev:	Pointer to slave device for this controller.
> + * @serdev:	Pointer to active slave device for this controller.
>   * @ops:	Controller operations.
> + * @mux:	Slave multiplexer control.
> + * @mux_do_not_deselect: Set if slave selection failed.
>   */
>  struct serdev_controller {
>  	struct device		dev;
>  	unsigned int		nr;
>  	struct serdev_device	*serdev;
>  	const struct serdev_controller_ops *ops;
> +	struct mux_control	*mux;
> +	int			mux_do_not_deselect;
>  };
>  
>  static inline struct serdev_controller *to_serdev_controller(struct device *d)
> @@ -172,7 +180,7 @@ static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl
>  {
>  	struct serdev_device *serdev = ctrl->serdev;
>  
> -	if (!serdev || !serdev->ops->write_wakeup)
> +	if (!serdev || !serdev->ops || !serdev->ops->write_wakeup)
>  		return;
>  
>  	serdev->ops->write_wakeup(serdev);
> @@ -184,7 +192,7 @@ static inline int serdev_controller_receive_buf(struct serdev_controller *ctrl,
>  {
>  	struct serdev_device *serdev = ctrl->serdev;
>  
> -	if (!serdev || !serdev->ops->receive_buf)
> +	if (!serdev || !serdev->ops || !serdev->ops->receive_buf)
>  		return -EINVAL;
>  
>  	return serdev->ops->receive_buf(serdev, data, count);
> @@ -204,6 +212,8 @@ void serdev_device_write_wakeup(struct serdev_device *);
>  int serdev_device_write(struct serdev_device *, const unsigned char *, size_t, unsigned long);
>  void serdev_device_write_flush(struct serdev_device *);
>  int serdev_device_write_room(struct serdev_device *);
> +int serdev_device_mux_select(struct serdev_device *);
> +int serdev_device_mux_deselect(struct serdev_device *);
>  
>  /*
>   * serdev device driver functions
>
Ulrich Hecht Aug. 16, 2017, 1:23 p.m. UTC | #3 
On Wed, Jul 19, 2017 at 1:06 AM, Rob Herring <robh@kernel.org> wrote:
>>  static inline struct serdev_controller *to_serdev_controller(struct device *d)
>> @@ -172,7 +180,7 @@ static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl
>>  {
>>         struct serdev_device *serdev = ctrl->serdev;
>>
>> -       if (!serdev || !serdev->ops->write_wakeup)
>> +       if (!serdev || !serdev->ops || !serdev->ops->write_wakeup)
>
> When is ops ever NULL? Should be a separate change AFIACT.

I dumped it; IIRC that happened once during development due to a bug elsewhere.

CU
Uli
diff mbox

Patch

diff --git a/drivers/tty/serdev/Kconfig b/drivers/tty/serdev/Kconfig
index cdc6b82..9096b71 100644
--- a/drivers/tty/serdev/Kconfig
+++ b/drivers/tty/serdev/Kconfig
@@ -13,4 +13,7 @@  config SERIAL_DEV_CTRL_TTYPORT
 	depends on TTY
 	depends on SERIAL_DEV_BUS != m
 
+config SERIAL_DEV_MUX
+	bool "Serial device multiplexer support"
+
 endif
diff --git a/drivers/tty/serdev/Makefile b/drivers/tty/serdev/Makefile
index 0cbdb94..d713381 100644
--- a/drivers/tty/serdev/Makefile
+++ b/drivers/tty/serdev/Makefile
@@ -1,5 +1,6 @@ 
 serdev-objs := core.o
 
 obj-$(CONFIG_SERIAL_DEV_BUS) += serdev.o
+obj-$(CONFIG_SERIAL_DEV_MUX) += mux.o
 
 obj-$(CONFIG_SERIAL_DEV_CTRL_TTYPORT) += serdev-ttyport.o
diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index 1fbaa4c..92c5bfa 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -305,7 +305,8 @@  struct serdev_device *serdev_device_alloc(struct serdev_controller *ctrl)
 		return NULL;
 
 	serdev->ctrl = ctrl;
-	ctrl->serdev = serdev;
+	if (!ctrl->serdev)
+		ctrl->serdev = serdev;
 	device_initialize(&serdev->dev);
 	serdev->dev.parent = &ctrl->dev;
 	serdev->dev.bus = &serdev_bus_type;
@@ -368,6 +369,8 @@  static int of_serdev_register_devices(struct serdev_controller *ctrl)
 	struct serdev_device *serdev = NULL;
 	int err;
 	bool found = false;
+	int nr = 0;
+	u32 reg;
 
 	for_each_available_child_of_node(ctrl->dev.of_node, node) {
 		if (!of_get_property(node, "compatible", NULL))
@@ -380,6 +383,10 @@  static int of_serdev_register_devices(struct serdev_controller *ctrl)
 			continue;
 
 		serdev->dev.of_node = node;
+		serdev->nr = nr++;
+
+		if (!of_property_read_u32(node, "reg", &reg))
+			serdev->mux_addr = reg;
 
 		err = serdev_device_add(serdev);
 		if (err) {
@@ -414,6 +421,11 @@  int serdev_controller_add(struct serdev_controller *ctrl)
 	if (ret)
 		return ret;
 
+#ifdef CONFIG_SERIAL_DEV_MUX
+	if (of_serdev_register_mux(ctrl) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
+#endif
+
 	ret = of_serdev_register_devices(ctrl);
 	if (ret)
 		goto out_dev_del;
diff --git a/drivers/tty/serdev/mux.c b/drivers/tty/serdev/mux.c
new file mode 100644
index 0000000..fc9405b
--- /dev/null
+++ b/drivers/tty/serdev/mux.c
@@ -0,0 +1,66 @@ 
+/*
+ * Copyright (C) 2017 Ulrich Hecht
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only 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/mux/consumer.h>
+#include <linux/mux/driver.h>
+#include <linux/of_gpio.h>
+#include <linux/serdev.h>
+#include <linux/slab.h>
+
+int serdev_device_mux_select(struct serdev_device *serdev)
+{
+	struct mux_control *mux = serdev->ctrl->mux;
+	int ret;
+
+	if (!mux)
+		return -EINVAL;
+
+	ret = mux_control_select(mux, serdev->mux_addr);
+	serdev->ctrl->mux_do_not_deselect = ret < 0;
+
+	serdev->ctrl->serdev = serdev;
+
+	return ret;
+}
+
+int serdev_device_mux_deselect(struct serdev_device *serdev)
+{
+	struct mux_control *mux = serdev->ctrl->mux;
+
+	if (!mux)
+		return -EINVAL;
+
+	if (!serdev->ctrl->mux_do_not_deselect)
+		return mux_control_deselect(mux);
+	else
+		return 0;
+}
+
+int of_serdev_register_mux(struct serdev_controller *ctrl)
+{
+	struct mux_control *mux;
+	struct device *dev = &ctrl->dev;
+
+	mux = devm_mux_control_get(dev, NULL);
+
+	if (IS_ERR(mux)) {
+		if (PTR_ERR(mux) != -EPROBE_DEFER)
+			dev_err(dev, "failed to get control mux\n");
+		return PTR_ERR(mux);
+	}
+
+	ctrl->mux = mux;
+
+	return 0;
+}
+
diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index 8b67fcd..26d5994 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -17,6 +17,7 @@ 
 #include <linux/device.h>
 #include <linux/termios.h>
 #include <linux/delay.h>
+#include <linux/rtmutex.h>
 
 struct serdev_controller;
 struct serdev_device;
@@ -51,6 +52,7 @@  struct serdev_device {
 	const struct serdev_device_ops *ops;
 	struct completion write_comp;
 	struct mutex write_lock;
+	int mux_addr;
 };
 
 static inline struct serdev_device *to_serdev_device(struct device *d)
@@ -76,6 +78,8 @@  static inline struct serdev_device_driver *to_serdev_device_driver(struct device
 	return container_of(d, struct serdev_device_driver, driver);
 }
 
+int of_serdev_register_mux(struct serdev_controller *ctrl);
+
 /*
  * serdev controller structures
  */
@@ -97,14 +101,18 @@  struct serdev_controller_ops {
  * struct serdev_controller - interface to the serdev controller
  * @dev:	Driver model representation of the device.
  * @nr:		number identifier for this controller/bus.
- * @serdev:	Pointer to slave device for this controller.
+ * @serdev:	Pointer to active slave device for this controller.
  * @ops:	Controller operations.
+ * @mux:	Slave multiplexer control.
+ * @mux_do_not_deselect: Set if slave selection failed.
  */
 struct serdev_controller {
 	struct device		dev;
 	unsigned int		nr;
 	struct serdev_device	*serdev;
 	const struct serdev_controller_ops *ops;
+	struct mux_control	*mux;
+	int			mux_do_not_deselect;
 };
 
 static inline struct serdev_controller *to_serdev_controller(struct device *d)
@@ -172,7 +180,7 @@  static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl
 {
 	struct serdev_device *serdev = ctrl->serdev;
 
-	if (!serdev || !serdev->ops->write_wakeup)
+	if (!serdev || !serdev->ops || !serdev->ops->write_wakeup)
 		return;
 
 	serdev->ops->write_wakeup(serdev);
@@ -184,7 +192,7 @@  static inline int serdev_controller_receive_buf(struct serdev_controller *ctrl,
 {
 	struct serdev_device *serdev = ctrl->serdev;
 
-	if (!serdev || !serdev->ops->receive_buf)
+	if (!serdev || !serdev->ops || !serdev->ops->receive_buf)
 		return -EINVAL;
 
 	return serdev->ops->receive_buf(serdev, data, count);
@@ -204,6 +212,8 @@  void serdev_device_write_wakeup(struct serdev_device *);
 int serdev_device_write(struct serdev_device *, const unsigned char *, size_t, unsigned long);
 void serdev_device_write_flush(struct serdev_device *);
 int serdev_device_write_room(struct serdev_device *);
+int serdev_device_mux_select(struct serdev_device *);
+int serdev_device_mux_deselect(struct serdev_device *);
 
 /*
  * serdev device driver functions