[v7,3/7] mfd: Add base driver for Netronix embedded controller

Commit Message

J. Neuschäfer Jan. 9, 2021, 6:02 p.m. UTC

The Netronix embedded controller is a microcontroller found in some
e-book readers designed by the original design manufacturer Netronix,
Inc. It contains RTC, battery monitoring, system power management, and
PWM functionality.

This driver implements register access and version detection.

Third-party hardware documentation is available at:

  https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller

The EC supports interrupts, but the driver doesn't make use of them so
far.

Signed-off-by: Jonathan Neuschäfer <[e-mail]>
Acked-for-MFD-by: Lee Jones <[e-mail]>
---
v7:
- Add #define for version number (suggested by Lee Jones).

v6:
- https://lore.kernel.org/lkml/[e-mail]/
- Add Lee Jones' ACK

v5:
- no changes

v4:
- https://lore.kernel.org/lkml/[e-mail]/
- include asm/unaligned.h after linux/*
- Use put_unaligned_be16 instead of open-coded big-endian packing
- Clarify that 0x90=0xff00 causes an error in downstream kernel too
- Add commas after non-sentinel positions
- ntxec.h: declare structs device and regmap
- Replace WARN_ON usage and add comments to explain errors
- Replace dev_alert with dev_warn when the result isn't handled
- Change subdevice registration error message to dev_err
- Declare ntxec_reg8 as returning __be16
- Restructure version detection code
- Spell out ODM

v3:
- https://lore.kernel.org/lkml/[e-mail]/
- Add (EC) to CONFIG_MFD_NTXEC prompt
- Relicense as GPLv2 or later
- Add email address to copyright line
- remove empty lines in ntxec_poweroff and ntxec_restart functions
- Split long lines
- Remove 'Install ... handler' comments
- Make naming of struct i2c_client parameter consistent
- Remove struct ntxec_info
- Rework 'depends on' lines in Kconfig, hard-depend on I2C, select REGMAP_I2C and
  MFD_CORE
- Register subdevices via mfd_cells
- Move 8-bit register conversion to ntxec.h

v2:
- https://lore.kernel.org/lkml/[e-mail]/
- Add a description of the device to the patch text
- Unify spelling as 'Netronix embedded controller'.
  'Netronix' is the proper name of the manufacturer, but 'embedded controller'
  is just a label that I have assigned to the device.
- Switch to regmap, avoid regmap use in poweroff and reboot handlers.
  Inspired by cf84dc0bb40f4 ("mfd: rn5t618: Make restart handler atomic safe")
- Use a list of known-working firmware versions instead of checking for a
  known-incompatible version
- Prefix registers with NTXEC_REG_
- Define register values as constants
- Various style cleanups as suggested by Lee Jones
- Don't align = signs in struct initializers [Uwe Kleine-König]
- Don't use dev_dbg for an error message
- Explain sleep in poweroff handler
- Remove (struct ntxec).client
- Switch to .probe_new in i2c driver
- Add .remove callback
- Make CONFIG_MFD_NTXEC a tristate option
---
 drivers/mfd/Kconfig       |  11 ++
 drivers/mfd/Makefile      |   1 +
 drivers/mfd/ntxec.c       | 216 ++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/ntxec.h |  37 +++++++
 4 files changed, 265 insertions(+)
 create mode 100644 drivers/mfd/ntxec.c
 create mode 100644 include/linux/mfd/ntxec.h

--
2.29.2

Comments

Andreas Kemnade Jan. 12, 2021, 7:36 p.m. UTC | #1

On Sat,  9 Jan 2021 19:02:16 +0100
Jonathan Neuschäfer <[e-mail]> wrote:

> The Netronix embedded controller is a microcontroller found in some
> e-book readers designed by the original design manufacturer Netronix,
> Inc. It contains RTC, battery monitoring, system power management, and
> PWM functionality.
> 
> This driver implements register access and version detection.
> 
> Third-party hardware documentation is available at:
> 
>   https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller
> 
> The EC supports interrupts, but the driver doesn't make use of them so
> far.
> 
> Signed-off-by: Jonathan Neuschäfer <[e-mail]>
> Acked-for-MFD-by: Lee Jones <[e-mail]>
> ---
> v7:
> - Add #define for version number (suggested by Lee Jones).
> 
> v6:
> - https://lore.kernel.org/lkml/[e-mail]/
> - Add Lee Jones' ACK
> 
> v5:
> - no changes
> 
> v4:
> - https://lore.kernel.org/lkml/[e-mail]/
> - include asm/unaligned.h after linux/*
> - Use put_unaligned_be16 instead of open-coded big-endian packing
> - Clarify that 0x90=0xff00 causes an error in downstream kernel too
> - Add commas after non-sentinel positions
> - ntxec.h: declare structs device and regmap
> - Replace WARN_ON usage and add comments to explain errors
> - Replace dev_alert with dev_warn when the result isn't handled
> - Change subdevice registration error message to dev_err
> - Declare ntxec_reg8 as returning __be16
> - Restructure version detection code
> - Spell out ODM
> 
> v3:
> - https://lore.kernel.org/lkml/[e-mail]/
> - Add (EC) to CONFIG_MFD_NTXEC prompt
> - Relicense as GPLv2 or later
> - Add email address to copyright line
> - remove empty lines in ntxec_poweroff and ntxec_restart functions
> - Split long lines
> - Remove 'Install ... handler' comments
> - Make naming of struct i2c_client parameter consistent
> - Remove struct ntxec_info
> - Rework 'depends on' lines in Kconfig, hard-depend on I2C, select REGMAP_I2C and
>   MFD_CORE
> - Register subdevices via mfd_cells
> - Move 8-bit register conversion to ntxec.h
> 
> v2:
> - https://lore.kernel.org/lkml/[e-mail]/
> - Add a description of the device to the patch text
> - Unify spelling as 'Netronix embedded controller'.
>   'Netronix' is the proper name of the manufacturer, but 'embedded controller'
>   is just a label that I have assigned to the device.
> - Switch to regmap, avoid regmap use in poweroff and reboot handlers.
>   Inspired by cf84dc0bb40f4 ("mfd: rn5t618: Make restart handler atomic safe")
> - Use a list of known-working firmware versions instead of checking for a
>   known-incompatible version
> - Prefix registers with NTXEC_REG_
> - Define register values as constants
> - Various style cleanups as suggested by Lee Jones
> - Don't align = signs in struct initializers [Uwe Kleine-König]
> - Don't use dev_dbg for an error message
> - Explain sleep in poweroff handler
> - Remove (struct ntxec).client
> - Switch to .probe_new in i2c driver
> - Add .remove callback
> - Make CONFIG_MFD_NTXEC a tristate option
> ---
>  drivers/mfd/Kconfig       |  11 ++
>  drivers/mfd/Makefile      |   1 +
>  drivers/mfd/ntxec.c       | 216 ++++++++++++++++++++++++++++++++++++++
>  include/linux/mfd/ntxec.h |  37 +++++++
>  4 files changed, 265 insertions(+)
>  create mode 100644 drivers/mfd/ntxec.c
>  create mode 100644 include/linux/mfd/ntxec.h
> 
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index bdfce7b156216..4280bcd47ec7d 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -976,6 +976,17 @@ config MFD_VIPERBOARD
>  	  You need to select the mfd cell drivers separately.
>  	  The drivers do not support all features the board exposes.
> 
> +config MFD_NTXEC
> +	tristate "Netronix embedded controller (EC)"
> +	depends on OF || COMPILE_TEST
> +	depends on I2C
> +	select REGMAP_I2C
> +	select MFD_CORE
> +	help
> +	  Say yes here if you want to support the embedded controller found in
> +	  certain e-book readers designed by the original design manufacturer
> +	  Netronix.
> +
>  config MFD_RETU
>  	tristate "Nokia Retu and Tahvo multi-function device"
>  	select MFD_CORE
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index 14fdb188af022..948a3bf8e3e57 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -219,6 +219,7 @@ obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+= intel_pmc_bxt.o
>  obj-$(CONFIG_MFD_INTEL_PMT)	+= intel_pmt.o
>  obj-$(CONFIG_MFD_PALMAS)	+= palmas.o
>  obj-$(CONFIG_MFD_VIPERBOARD)    += viperboard.o
> +obj-$(CONFIG_MFD_NTXEC)		+= ntxec.o
>  obj-$(CONFIG_MFD_RC5T583)	+= rc5t583.o rc5t583-irq.o
>  obj-$(CONFIG_MFD_RK808)		+= rk808.o
>  obj-$(CONFIG_MFD_RN5T618)	+= rn5t618.o
> diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
> new file mode 100644
> index 0000000000000..22ed2ef0669cb
> --- /dev/null
> +++ b/drivers/mfd/ntxec.c
> @@ -0,0 +1,216 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * The Netronix embedded controller is a microcontroller found in some
> + * e-book readers designed by the original design manufacturer Netronix, Inc.
> + * It contains RTC, battery monitoring, system power management, and PWM
> + * functionality.
> + *
> + * This driver implements register access, version detection, and system
> + * power-off/reset.
> + *
> + * Copyright 2020 Jonathan Neuschäfer <[e-mail]>
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <linux/mfd/core.h>
> +#include <linux/mfd/ntxec.h>
> +#include <linux/module.h>
> +#include <linux/pm.h>
> +#include <linux/reboot.h>
> +#include <linux/regmap.h>
> +#include <linux/types.h>
> +#include <asm/unaligned.h>
> +
> +#define NTXEC_REG_VERSION	0x00
> +#define NTXEC_REG_POWEROFF	0x50
> +#define NTXEC_REG_POWERKEEP	0x70
> +#define NTXEC_REG_RESET		0x90
> +
> +#define NTXEC_POWEROFF_VALUE	0x0100
> +#define NTXEC_POWERKEEP_VALUE	0x0800
> +#define NTXEC_RESET_VALUE	0xff00
> +
> +static struct i2c_client *poweroff_restart_client;
> +
> +static void ntxec_poweroff(void)
> +{
> +	int res;
> +	u8 buf[3] = { NTXEC_REG_POWEROFF };
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = poweroff_restart_client->addr,
> +			.flags = 0,
> +			.len = sizeof(buf),
> +			.buf = buf,
> +		},
> +	};
> +
> +	put_unaligned_be16(NTXEC_POWEROFF_VALUE, buf + 1);
> +
> +	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +	if (res < 0)
> +		dev_warn(&poweroff_restart_client->dev,
> +			 "Failed to power off (err = %d)\n", res);
> +
> +	/*
> +	 * The time from the register write until the host CPU is powered off
> +	 * has been observed to be about 2.5 to 3 seconds. Sleep long enough to
> +	 * safely avoid returning from the poweroff handler.
> +	 */
> +	msleep(5000);
> +}
> +
> +static int ntxec_restart(struct notifier_block *nb,
> +			 unsigned long action, void *data)
> +{
> +	int res;
> +	u8 buf[3] = { NTXEC_REG_RESET };
> +	/*
> +	 * NOTE: The lower half of the reset value is not sent, because sending
> +	 * it causes an I2C error. (The reset handler in the downstream driver
> +	 * does send the full two-byte value, but doesn't check the result).
> +	 */
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = poweroff_restart_client->addr,
> +			.flags = 0,
> +			.len = sizeof(buf) - 1,
> +			.buf = buf,
> +		},
> +	};
> +
> +	put_unaligned_be16(NTXEC_RESET_VALUE, buf + 1);
> +
> +	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +	if (res < 0)
> +		dev_warn(&poweroff_restart_client->dev,
> +			 "Failed to restart (err = %d)\n", res);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block ntxec_restart_handler = {
> +	.notifier_call = ntxec_restart,
> +	.priority = 128,
> +};
> +
> +static const struct regmap_config regmap_config = {
> +	.name = "ntxec",
> +	.reg_bits = 8,
> +	.val_bits = 16,
> +	.cache_type = REGCACHE_NONE,
> +	.val_format_endian = REGMAP_ENDIAN_BIG,
> +};
> +
> +static const struct mfd_cell ntxec_subdevices[] = {
> +	{ .name = "ntxec-rtc" },
> +	{ .name = "ntxec-pwm" },
> +};
> +
> +static int ntxec_probe(struct i2c_client *client)
> +{
> +	struct ntxec *ec;
> +	unsigned int version;
> +	int res;
> +
> +	ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
> +	if (!ec)
> +		return -ENOMEM;
> +
> +	ec->dev = &client->dev;
> +
> +	ec->regmap = devm_regmap_init_i2c(client, &regmap_config);
> +	if (IS_ERR(ec->regmap)) {
> +		dev_err(ec->dev, "Failed to set up regmap for device\n");
> +		return res;
> +	}
> +
> +	/* Determine the firmware version */
> +	res = regmap_read(ec->regmap, NTXEC_REG_VERSION, &version);
> +	if (res < 0) {
> +		dev_err(ec->dev, "Failed to read firmware version number\n");
> +		return res;
> +	}
> +
> +	/* Bail out if we encounter an unknown firmware version */
> +	switch (version) {
> +	case NTXEC_VERSION_KOBO_AURA:
> +		break;
> +	default:
> +		dev_err(ec->dev,
> +			"Netronix embedded controller version %04x is not supported.\n",
> +			version);
> +		return -ENODEV;
> +	}
> +
> +	dev_info(ec->dev,
> +		 "Netronix embedded controller version %04x detected.\n", version);
> +
> +	if (of_device_is_system_power_controller(ec->dev->of_node)) {
> +		/*
> +		 * Set the 'powerkeep' bit. This is necessary on some boards
> +		 * in order to keep the system running.
> +		 */
> +		res = regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
> +				   NTXEC_POWERKEEP_VALUE);
> +		if (res < 0)
> +			return res;
> +
> +		if (poweroff_restart_client)
> +			/*
> +			 * Another instance of the driver already took
> +			 * poweroff/restart duties.
> +			 */
> +			dev_err(ec->dev, "poweroff_restart_client already assigned\n");
> +		else
> +			poweroff_restart_client = client;
> +
> +		if (pm_power_off)
> +			/* Another driver already registered a poweroff handler. */
> +			dev_err(ec->dev, "pm_power_off already assigned\n");
> +		else
> +			pm_power_off = ntxec_poweroff;
> +
> +		res = register_restart_handler(&ntxec_restart_handler);
> +		if (res)
> +			dev_err(ec->dev,
> +				"Failed to register restart handler: %d\n", res);
> +	}
> +
> +	i2c_set_clientdata(client, ec);
> +
> +	res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE, ntxec_subdevices,
> +				   ARRAY_SIZE(ntxec_subdevices), NULL, 0, NULL);
> +	if (res)
> +		dev_err(ec->dev, "Failed to add subdevices: %d\n", res);
> +
> +	return res;
> +}
> +
> +static int ntxec_remove(struct i2c_client *client)
> +{
> +	if (client == poweroff_restart_client) {
> +		poweroff_restart_client = NULL;
> +		pm_power_off = NULL;
> +		unregister_restart_handler(&ntxec_restart_handler);
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id of_ntxec_match_table[] = {
> +	{ .compatible = "netronix,ntxec", },
> +	{}
> +};
> +
MODULE_DEVICE_TABLE?

> +static struct i2c_driver ntxec_driver = {
> +	.driver = {
> +		.name = "ntxec",
> +		.of_match_table = of_ntxec_match_table,
> +	},
> +	.probe_new = ntxec_probe,
> +	.remove = ntxec_remove,
> +};
> +module_i2c_driver(ntxec_driver);

MODULE_LICENSE()?

modpost moans about that here.

Regards,
Andreas

Lee Jones Jan. 13, 2021, 8:03 a.m. UTC | #2

On Tue, 12 Jan 2021, Andreas Kemnade wrote:

> On Sat,  9 Jan 2021 19:02:16 +0100
> Jonathan Neuschäfer <[e-mail]> wrote:
> 
> > The Netronix embedded controller is a microcontroller found in some
> > e-book readers designed by the original design manufacturer Netronix,
> > Inc. It contains RTC, battery monitoring, system power management, and
> > PWM functionality.
> > 
> > This driver implements register access and version detection.
> > 
> > Third-party hardware documentation is available at:
> > 
> >   https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller
> > 
> > The EC supports interrupts, but the driver doesn't make use of them so
> > far.
> > 
> > Signed-off-by: Jonathan Neuschäfer <[e-mail]>
> > Acked-for-MFD-by: Lee Jones <[e-mail]>

[...]

> > +static const struct of_device_id of_ntxec_match_table[] = {
> > +	{ .compatible = "netronix,ntxec", },
> > +	{}
> > +};
> > +
> MODULE_DEVICE_TABLE?
> 
> > +static struct i2c_driver ntxec_driver = {
> > +	.driver = {
> > +		.name = "ntxec",
> > +		.of_match_table = of_ntxec_match_table,
> > +	},
> > +	.probe_new = ntxec_probe,
> > +	.remove = ntxec_remove,
> > +};
> > +module_i2c_driver(ntxec_driver);
> 
> MODULE_LICENSE()?
> 
> modpost moans about that here.

Andreas, would you be kind enough to snip/trim your replies in future
please.  It would save a *lot* of people a little bit of time (which
adds up fast).  TIA.

J. Neuschäfer Jan. 14, 2021, 6:56 p.m. UTC | #3

On Tue, Jan 12, 2021 at 08:36:49PM +0100, Andreas Kemnade wrote:
> On Sat,  9 Jan 2021 19:02:16 +0100
> Jonathan Neuschäfer <[e-mail]> wrote:
[...]
> > +static const struct of_device_id of_ntxec_match_table[] = {
> > +	{ .compatible = "netronix,ntxec", },
> > +	{}
> > +};
> > +
> MODULE_DEVICE_TABLE?

Yes, good idea.

> > +static struct i2c_driver ntxec_driver = {
> > +	.driver = {
> > +		.name = "ntxec",
> > +		.of_match_table = of_ntxec_match_table,
> > +	},
> > +	.probe_new = ntxec_probe,
> > +	.remove = ntxec_remove,
> > +};
> > +module_i2c_driver(ntxec_driver);
> 
> MODULE_LICENSE()?
> 
> modpost moans about that here.

I forgot those. Thanks for noticing.
I'll add the MODULE_ lines in v8.



Thanks,
Jonathan

Patch

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index bdfce7b156216..4280bcd47ec7d 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -976,6 +976,17 @@  config MFD_VIPERBOARD
 	  You need to select the mfd cell drivers separately.
 	  The drivers do not support all features the board exposes.

+config MFD_NTXEC
+	tristate "Netronix embedded controller (EC)"
+	depends on OF || COMPILE_TEST
+	depends on I2C
+	select REGMAP_I2C
+	select MFD_CORE
+	help
+	  Say yes here if you want to support the embedded controller found in
+	  certain e-book readers designed by the original design manufacturer
+	  Netronix.
+
 config MFD_RETU
 	tristate "Nokia Retu and Tahvo multi-function device"
 	select MFD_CORE
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index 14fdb188af022..948a3bf8e3e57 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -219,6 +219,7 @@  obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+= intel_pmc_bxt.o
 obj-$(CONFIG_MFD_INTEL_PMT)	+= intel_pmt.o
 obj-$(CONFIG_MFD_PALMAS)	+= palmas.o
 obj-$(CONFIG_MFD_VIPERBOARD)    += viperboard.o
+obj-$(CONFIG_MFD_NTXEC)		+= ntxec.o
 obj-$(CONFIG_MFD_RC5T583)	+= rc5t583.o rc5t583-irq.o
 obj-$(CONFIG_MFD_RK808)		+= rk808.o
 obj-$(CONFIG_MFD_RN5T618)	+= rn5t618.o
diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
new file mode 100644
index 0000000000000..22ed2ef0669cb
--- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,216 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the original design manufacturer Netronix, Inc.
+ * It contains RTC, battery monitoring, system power management, and PWM
+ * functionality.
+ *
+ * This driver implements register access, version detection, and system
+ * power-off/reset.
+ *
+ * Copyright 2020 Jonathan Neuschäfer <[e-mail]>
+ */
+
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+#include <asm/unaligned.h>
+
+#define NTXEC_REG_VERSION	0x00
+#define NTXEC_REG_POWEROFF	0x50
+#define NTXEC_REG_POWERKEEP	0x70
+#define NTXEC_REG_RESET		0x90
+
+#define NTXEC_POWEROFF_VALUE	0x0100
+#define NTXEC_POWERKEEP_VALUE	0x0800
+#define NTXEC_RESET_VALUE	0xff00
+
+static struct i2c_client *poweroff_restart_client;
+
+static void ntxec_poweroff(void)
+{
+	int res;
+	u8 buf[3] = { NTXEC_REG_POWEROFF };
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf,
+		},
+	};
+
+	put_unaligned_be16(NTXEC_POWEROFF_VALUE, buf + 1);
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (res < 0)
+		dev_warn(&poweroff_restart_client->dev,
+			 "Failed to power off (err = %d)\n", res);
+
+	/*
+	 * The time from the register write until the host CPU is powered off
+	 * has been observed to be about 2.5 to 3 seconds. Sleep long enough to
+	 * safely avoid returning from the poweroff handler.
+	 */
+	msleep(5000);
+}
+
+static int ntxec_restart(struct notifier_block *nb,
+			 unsigned long action, void *data)
+{
+	int res;
+	u8 buf[3] = { NTXEC_REG_RESET };
+	/*
+	 * NOTE: The lower half of the reset value is not sent, because sending
+	 * it causes an I2C error. (The reset handler in the downstream driver
+	 * does send the full two-byte value, but doesn't check the result).
+	 */
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf) - 1,
+			.buf = buf,
+		},
+	};
+
+	put_unaligned_be16(NTXEC_RESET_VALUE, buf + 1);
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+	if (res < 0)
+		dev_warn(&poweroff_restart_client->dev,
+			 "Failed to restart (err = %d)\n", res);
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ntxec_restart_handler = {
+	.notifier_call = ntxec_restart,
+	.priority = 128,
+};
+
+static const struct regmap_config regmap_config = {
+	.name = "ntxec",
+	.reg_bits = 8,
+	.val_bits = 16,
+	.cache_type = REGCACHE_NONE,
+	.val_format_endian = REGMAP_ENDIAN_BIG,
+};
+
+static const struct mfd_cell ntxec_subdevices[] = {
+	{ .name = "ntxec-rtc" },
+	{ .name = "ntxec-pwm" },
+};
+
+static int ntxec_probe(struct i2c_client *client)
+{
+	struct ntxec *ec;
+	unsigned int version;
+	int res;
+
+	ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
+	if (!ec)
+		return -ENOMEM;
+
+	ec->dev = &client->dev;
+
+	ec->regmap = devm_regmap_init_i2c(client, &regmap_config);
+	if (IS_ERR(ec->regmap)) {
+		dev_err(ec->dev, "Failed to set up regmap for device\n");
+		return res;
+	}
+
+	/* Determine the firmware version */
+	res = regmap_read(ec->regmap, NTXEC_REG_VERSION, &version);
+	if (res < 0) {
+		dev_err(ec->dev, "Failed to read firmware version number\n");
+		return res;
+	}
+
+	/* Bail out if we encounter an unknown firmware version */
+	switch (version) {
+	case NTXEC_VERSION_KOBO_AURA:
+		break;
+	default:
+		dev_err(ec->dev,
+			"Netronix embedded controller version %04x is not supported.\n",
+			version);
+		return -ENODEV;
+	}
+
+	dev_info(ec->dev,
+		 "Netronix embedded controller version %04x detected.\n", version);
+
+	if (of_device_is_system_power_controller(ec->dev->of_node)) {
+		/*
+		 * Set the 'powerkeep' bit. This is necessary on some boards
+		 * in order to keep the system running.
+		 */
+		res = regmap_write(ec->regmap, NTXEC_REG_POWERKEEP,
+				   NTXEC_POWERKEEP_VALUE);
+		if (res < 0)
+			return res;
+
+		if (poweroff_restart_client)
+			/*
+			 * Another instance of the driver already took
+			 * poweroff/restart duties.
+			 */
+			dev_err(ec->dev, "poweroff_restart_client already assigned\n");
+		else
+			poweroff_restart_client = client;
+
+		if (pm_power_off)
+			/* Another driver already registered a poweroff handler. */
+			dev_err(ec->dev, "pm_power_off already assigned\n");
+		else
+			pm_power_off = ntxec_poweroff;
+
+		res = register_restart_handler(&ntxec_restart_handler);
+		if (res)
+			dev_err(ec->dev,
+				"Failed to register restart handler: %d\n", res);
+	}
+
+	i2c_set_clientdata(client, ec);
+
+	res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE, ntxec_subdevices,
+				   ARRAY_SIZE(ntxec_subdevices), NULL, 0, NULL);
+	if (res)
+		dev_err(ec->dev, "Failed to add subdevices: %d\n", res);
+
+	return res;
+}
+
+static int ntxec_remove(struct i2c_client *client)
+{
+	if (client == poweroff_restart_client) {
+		poweroff_restart_client = NULL;
+		pm_power_off = NULL;
+		unregister_restart_handler(&ntxec_restart_handler);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id of_ntxec_match_table[] = {
+	{ .compatible = "netronix,ntxec", },
+	{}
+};
+
+static struct i2c_driver ntxec_driver = {
+	.driver = {
+		.name = "ntxec",
+		.of_match_table = of_ntxec_match_table,
+	},
+	.probe_new = ntxec_probe,
+	.remove = ntxec_remove,
+};
+module_i2c_driver(ntxec_driver);
diff --git a/include/linux/mfd/ntxec.h b/include/linux/mfd/ntxec.h
new file mode 100644
index 0000000000000..361204d125f1a
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,37 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Jonathan Neuschäfer
+ *
+ * Register access and version information for the Netronix embedded
+ * controller.
+ */
+
+#ifndef NTXEC_H
+#define NTXEC_H
+
+#include <linux/types.h>
+
+struct device;
+struct regmap;
+
+struct ntxec {
+	struct device *dev;
+	struct regmap *regmap;
+};
+
+/*
+ * Some registers, such as the battery status register (0x41), are in
+ * big-endian, but others only have eight significant bits, which are in the
+ * first byte transmitted over I2C (the MSB of the big-endian value).
+ * This convenience function converts an 8-bit value to 16-bit for use in the
+ * second kind of register.
+ */
+static inline __be16 ntxec_reg8(u8 value)
+{
+	return value << 8;
+}
+
+/* Known firmware versions */
+#define NTXEC_VERSION_KOBO_AURA	0xd726	/* found in Kobo Aura */
+
+#endif