diff mbox series

[v2,03/10] mfd: Add base driver for Netronix embedded controller

Message ID 20200905133230.1014581-4-j.neuschaefer@gmx.net
State Changes Requested
Headers show
Series Netronix embedded controller driver for Kobo and Tolino ebook readers | expand

Commit Message

Jonathan Neuschäfer Sept. 5, 2020, 1:32 p.m. UTC
The Netronix embedded controller is a microcontroller found in some
e-book readers designed by the ODM 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 <j.neuschaefer@gmx.net>
---

v2:
- 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       |   7 ++
 drivers/mfd/Makefile      |   1 +
 drivers/mfd/ntxec.c       | 217 ++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/ntxec.h |  24 +++++
 4 files changed, 249 insertions(+)
 create mode 100644 drivers/mfd/ntxec.c
 create mode 100644 include/linux/mfd/ntxec.h

--
2.28.0

Comments

Lee Jones Sept. 8, 2020, 1:29 p.m. UTC | #1
On Sat, 05 Sep 2020, Jonathan Neuschäfer wrote:

> The Netronix embedded controller is a microcontroller found in some
> e-book readers designed by the ODM 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 <j.neuschaefer@gmx.net>
> ---
> 
> v2:
> - 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       |   7 ++
>  drivers/mfd/Makefile      |   1 +
>  drivers/mfd/ntxec.c       | 217 ++++++++++++++++++++++++++++++++++++++
>  include/linux/mfd/ntxec.h |  24 +++++
>  4 files changed, 249 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 33df0837ab415..bab999081f32d 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -978,6 +978,13 @@ 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"

Nit: "Embedded Controller (EC)"

> +	depends on I2C && OF

	depends on (I2C && OF) || COMPILE_TEST

> +	help
> +	  Say yes here if you want to support the embedded controller found in
> +	  certain e-book readers designed by the ODM 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 a60e5f835283e..236a8acd917a0 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -217,6 +217,7 @@ obj-$(CONFIG_MFD_INTEL_MSIC)	+= intel_msic.o
>  obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+= intel_pmc_bxt.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..49cc4fa35b9fe
> --- /dev/null
> +++ b/drivers/mfd/ntxec.c
> @@ -0,0 +1,217 @@
> +// SPDX-License-Identifier: GPL-2.0-only

Why 2 only?

> +/*
> + * The Netronix embedded controller is a microcontroller found in some
> + * e-book readers designed by the ODM 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

Email?

> + */
> +
> +#include <asm/unaligned.h>
> +#include <linux/delay.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <linux/mfd/ntxec.h>
> +#include <linux/module.h>
> +#include <linux/of_platform.h>
> +#include <linux/pm.h>
> +#include <linux/reboot.h>
> +#include <linux/regmap.h>
> +#include <linux/types.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;
> +

Remove this line please.

> +	u8 buf[] = {
> +		NTXEC_REG_POWEROFF,
> +		(NTXEC_POWEROFF_VALUE >> 8) & 0xff,
> +		NTXEC_POWEROFF_VALUE & 0xff,
> +	};
> +

And this one.

> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = poweroff_restart_client->addr,
> +			.flags = 0,
> +			.len = sizeof(buf),
> +			.buf = buf
> +		}
> +	};
> +
> +	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +

And this one.

> +	if (res < 0)
> +		dev_alert(&poweroff_restart_client->dev, "Failed to power off (err = %d)\n", res);

This looks way over 80 chars.

Did you run checkpatch.pl?

> +	/*
> +	 * 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;
> +
> +	/*
> +	 * NOTE: The lower half of the reset value is not sent, because sending
> +	 * it causes an error
> +	 */
> +	u8 buf[] = {
> +		NTXEC_REG_RESET,
> +		(NTXEC_RESET_VALUE >> 8) & 0xff,
> +	};
> +
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = poweroff_restart_client->addr,
> +			.flags = 0,
> +			.len = sizeof(buf),
> +			.buf = buf
> +		}
> +	};
> +
> +	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> +
> +	if (res < 0)
> +		dev_alert(&poweroff_restart_client->dev, "Failed to restart (err = %d)\n", res);
> +
> +	return NOTIFY_DONE;
> +}

All as above for this function.

> +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 ntxec_info ntxec_known_versions[] = {
> +	{ 0xd726 }, /* found in Kobo Aura */
> +};
> +
> +static const struct ntxec_info *ntxec_lookup_info(u16 version)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(ntxec_known_versions); i++) {
> +		const struct ntxec_info *info = &ntxec_known_versions[i];
> +
> +		if (info->version == version)
> +			return info;
> +	}
> +
> +	return NULL;
> +}

Wait, what?  This is over-engineered.

Just have a look-up table (switch) of supported devices.

> +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;
> +	}
> +	dev_info(ec->dev,
> +		 "Netronix embedded controller version %04x detected.\n",
> +		 version);
> +
> +	/* Bail out if we encounter an unknown firmware version */
> +	ec->info = ntxec_lookup_info(version);
> +	if (!ec->info)
> +		return -EOPNOTSUPP;

#define EOPNOTSUPP      95      /* Operation not supported on transport endpoint */

I think you want:

#define ENODEV          19      /* No such device */

> +	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;
> +
> +		/* Install poweroff handler */

Don't think this comment is required.

> +		WARN_ON(poweroff_restart_client);
> +		poweroff_restart_client = client;
> +		if (pm_power_off)
> +			dev_err(ec->dev, "pm_power_off already assigned\n");
> +		else
> +			pm_power_off = ntxec_poweroff;
> +
> +		/* Install board reset handler */

Nor this.

> +		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);
> +
> +	return devm_of_platform_populate(ec->dev);
> +}
> +
> +static int ntxec_remove(struct i2c_client *i2c)

Why do you call it 'client' in .probe, but 'i2c' in .remove?

> +{
> +	if (i2c == 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..65e389af79da6
> --- /dev/null
> +++ b/include/linux/mfd/ntxec.h
> @@ -0,0 +1,24 @@
> +/* 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 ntxec_info {
> +	u16 version;
> +};
> +
> +struct ntxec {
> +	struct device *dev;
> +	struct regmap *regmap;

> +	const struct ntxec_info *info;

What is this used for?

> +};
> +
> +#endif
Jonathan Neuschäfer Sept. 10, 2020, 12:04 p.m. UTC | #2
On Tue, Sep 08, 2020 at 02:29:34PM +0100, Lee Jones wrote:
> On Sat, 05 Sep 2020, Jonathan Neuschäfer wrote:
[...]
> > +config MFD_NTXEC
> > +	tristate "Netronix embedded controller"
> 
> Nit: "Embedded Controller (EC)"

I intentionally left it lowercase, because the term 'embedded
controller' is not used in code coming from Netronix. It's just a label
that I found fitting to assign to the device. (In the vendor kernels
it's either called 'msp430', named after the TI MSP430 microcontroller
family, or 'uc', presumably for 'microcontroller')

Adding '(EC)' seems somewhat useful.

> 
> > +	depends on I2C && OF
> 
> 	depends on (I2C && OF) || COMPILE_TEST

Okay

> > +++ b/drivers/mfd/ntxec.c
> > @@ -0,0 +1,217 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> 
> Why 2 only?

No particular reason. If you prefer 2-or-later, I'll change it.

> > +/*
> > + * The Netronix embedded controller is a microcontroller found in some
> > + * e-book readers designed by the ODM 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
> 
> Email?

Alright, I'll add it

> > +static void ntxec_poweroff(void)
> > +{
> > +	int res;
> > +
> 
> Remove this line please.
> 
> > +	u8 buf[] = {
> > +		NTXEC_REG_POWEROFF,
> > +		(NTXEC_POWEROFF_VALUE >> 8) & 0xff,
> > +		NTXEC_POWEROFF_VALUE & 0xff,
> > +	};
> > +
> 
> And this one.
> 
> > +	struct i2c_msg msgs[] = {
> > +		{
> > +			.addr = poweroff_restart_client->addr,
> > +			.flags = 0,
> > +			.len = sizeof(buf),
> > +			.buf = buf
> > +		}
> > +	};
> > +
> > +	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
> > +
> 
> And this one.

Okay

> 
> > +	if (res < 0)
> > +		dev_alert(&poweroff_restart_client->dev, "Failed to power off (err = %d)\n", res);
> 
> This looks way over 80 chars.

Okay, I'll break it up.

> Did you run checkpatch.pl?

Yes, but it didn't complain about this line. - propabably because the
line length threshold in checkpatch has recently been increased to 100.

> > +	/*
> > +	 * 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)
[...]
> 
> All as above for this function.

Alright

> 
> > +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 ntxec_info ntxec_known_versions[] = {
> > +	{ 0xd726 }, /* found in Kobo Aura */
> > +};
> > +
> > +static const struct ntxec_info *ntxec_lookup_info(u16 version)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(ntxec_known_versions); i++) {
> > +		const struct ntxec_info *info = &ntxec_known_versions[i];
> > +
> > +		if (info->version == version)
> > +			return info;
> > +	}
> > +
> > +	return NULL;
> > +}
> 
> Wait, what?  This is over-engineered.

I thought it would be useful when we want to attach additional
information to specific versions.... okay, it is over-engineered.

> Just have a look-up table (switch) of supported devices.

Will do.

> 
> > +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;
> > +	}
> > +	dev_info(ec->dev,
> > +		 "Netronix embedded controller version %04x detected.\n",
> > +		 version);
> > +
> > +	/* Bail out if we encounter an unknown firmware version */
> > +	ec->info = ntxec_lookup_info(version);
> > +	if (!ec->info)
> > +		return -EOPNOTSUPP;
> 
> #define EOPNOTSUPP      95      /* Operation not supported on transport endpoint */
> 
> I think you want:
> 
> #define ENODEV          19      /* No such device */

Indeed, EOPNOTSUPP seems quite wrong here. I think I used ENOTSUPP at
some earlier point but moved away from it because it's one of the
internal error codes (≥512).

ENODEV makes sense when I read it as "Not a device that this driver can
deal with".

> 
> > +	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;
> > +
> > +		/* Install poweroff handler */
> 
> Don't think this comment is required.
> 
> > +		WARN_ON(poweroff_restart_client);
> > +		poweroff_restart_client = client;
> > +		if (pm_power_off)
> > +			dev_err(ec->dev, "pm_power_off already assigned\n");
> > +		else
> > +			pm_power_off = ntxec_poweroff;
> > +
> > +		/* Install board reset handler */
> 
> Nor this.

Alright, I'll remove them.

> > +		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);
> > +
> > +	return devm_of_platform_populate(ec->dev);
> > +}
> > +
> > +static int ntxec_remove(struct i2c_client *i2c)
> 
> Why do you call it 'client' in .probe, but 'i2c' in .remove?

No particular reason. I'll make them consistent.

> > +struct ntxec_info {
> > +	u16 version;
> > +};
> > +
> > +struct ntxec {
> > +	struct device *dev;
> > +	struct regmap *regmap;
> 
> > +	const struct ntxec_info *info;
> 
> What is this used for?

At this point, nothing. I'll remove it.


Thanks,
Jonathan Neuschäfer
diff mbox series

Patch

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 33df0837ab415..bab999081f32d 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -978,6 +978,13 @@  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"
+	depends on I2C && OF
+	help
+	  Say yes here if you want to support the embedded controller found in
+	  certain e-book readers designed by the ODM 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 a60e5f835283e..236a8acd917a0 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -217,6 +217,7 @@  obj-$(CONFIG_MFD_INTEL_MSIC)	+= intel_msic.o
 obj-$(CONFIG_MFD_INTEL_PMC_BXT)	+= intel_pmc_bxt.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..49cc4fa35b9fe
--- /dev/null
+++ b/drivers/mfd/ntxec.c
@@ -0,0 +1,217 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the ODM 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
+ */
+
+#include <asm/unaligned.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/pm.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+#include <linux/types.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[] = {
+		NTXEC_REG_POWEROFF,
+		(NTXEC_POWEROFF_VALUE >> 8) & 0xff,
+		NTXEC_POWEROFF_VALUE & 0xff,
+	};
+
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf
+		}
+	};
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+
+	if (res < 0)
+		dev_alert(&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;
+
+	/*
+	 * NOTE: The lower half of the reset value is not sent, because sending
+	 * it causes an error
+	 */
+	u8 buf[] = {
+		NTXEC_REG_RESET,
+		(NTXEC_RESET_VALUE >> 8) & 0xff,
+	};
+
+	struct i2c_msg msgs[] = {
+		{
+			.addr = poweroff_restart_client->addr,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf
+		}
+	};
+
+	res = i2c_transfer(poweroff_restart_client->adapter, msgs, ARRAY_SIZE(msgs));
+
+	if (res < 0)
+		dev_alert(&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 ntxec_info ntxec_known_versions[] = {
+	{ 0xd726 }, /* found in Kobo Aura */
+};
+
+static const struct ntxec_info *ntxec_lookup_info(u16 version)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ntxec_known_versions); i++) {
+		const struct ntxec_info *info = &ntxec_known_versions[i];
+
+		if (info->version == version)
+			return info;
+	}
+
+	return NULL;
+}
+
+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;
+	}
+	dev_info(ec->dev,
+		 "Netronix embedded controller version %04x detected.\n",
+		 version);
+
+	/* Bail out if we encounter an unknown firmware version */
+	ec->info = ntxec_lookup_info(version);
+	if (!ec->info)
+		return -EOPNOTSUPP;
+
+	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;
+
+		/* Install poweroff handler */
+		WARN_ON(poweroff_restart_client);
+		poweroff_restart_client = client;
+		if (pm_power_off)
+			dev_err(ec->dev, "pm_power_off already assigned\n");
+		else
+			pm_power_off = ntxec_poweroff;
+
+		/* Install board reset handler */
+		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);
+
+	return devm_of_platform_populate(ec->dev);
+}
+
+static int ntxec_remove(struct i2c_client *i2c)
+{
+	if (i2c == 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..65e389af79da6
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,24 @@ 
+/* 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 ntxec_info {
+	u16 version;
+};
+
+struct ntxec {
+	struct device *dev;
+	struct regmap *regmap;
+	const struct ntxec_info *info;
+};
+
+#endif