diff mbox series

[v4,3/7] mfd: Add base driver for Netronix embedded controller

Message ID 20201122222739.1455132-4-j.neuschaefer@gmx.net
State Superseded
Headers show
Series [v4,1/7] dt-bindings: Add vendor prefix for Netronix, Inc. | expand

Commit Message

J. Neuschäfer Nov. 22, 2020, 10:27 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 <j.neuschaefer@gmx.net>
---

v4:
- 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/20200924192455.2484005-4-j.neuschaefer@gmx.net/
- 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/20200905133230.1014581-4-j.neuschaefer@gmx.net/
- 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 |  34 ++++++
 4 files changed, 262 insertions(+)
 create mode 100644 drivers/mfd/ntxec.c
 create mode 100644 include/linux/mfd/ntxec.h

--
2.29.2

Comments

Lee Jones Dec. 2, 2020, 1:05 p.m. UTC | #1
On Sun, 22 Nov 2020, Jonathan Neuschäfer 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 <j.neuschaefer@gmx.net>

> ---

> 

> v4:

> - 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/20200924192455.2484005-4-j.neuschaefer@gmx.net/

> - 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/20200905133230.1014581-4-j.neuschaefer@gmx.net/

> - 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 |  34 ++++++

>  4 files changed, 262 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 8b99a13669bfc..d96751f884dc6 100644

> --- a/drivers/mfd/Kconfig

> +++ b/drivers/mfd/Kconfig

> @@ -990,6 +990,17 @@ 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 1780019d24748..815c99b84019e 100644

> --- a/drivers/mfd/Makefile

> +++ b/drivers/mfd/Makefile

> @@ -218,6 +218,7 @@ 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..c1510711d7363

> --- /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 <j.neuschaefer@gmx.net>

> + */

> +

> +#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 0xd726: /* found in Kobo Aura */


No magic numbers.

Please submit a subsequent patch to define this.

> +		break;

> +	default:

> +		dev_err(ec->dev,

> +			"Netronix embedded controller version %04x is not supported.\n",

> +			version);

> +		return -ENODEV;

> +	}



Applied, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
Lee Jones Dec. 2, 2020, 1:06 p.m. UTC | #2
On Wed, 02 Dec 2020, Lee Jones wrote:

> On Sun, 22 Nov 2020, Jonathan Neuschäfer 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 <j.neuschaefer@gmx.net>

> > ---

> > 

> > v4:

> > - 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/20200924192455.2484005-4-j.neuschaefer@gmx.net/

> > - 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/20200905133230.1014581-4-j.neuschaefer@gmx.net/

> > - 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 |  34 ++++++

> >  4 files changed, 262 insertions(+)

> >  create mode 100644 drivers/mfd/ntxec.c

> >  create mode 100644 include/linux/mfd/ntxec.h


[...]

> > +	/* Bail out if we encounter an unknown firmware version */

> > +	switch (version) {

> > +	case 0xd726: /* found in Kobo Aura */

> 

> No magic numbers.

> 

> Please submit a subsequent patch to define this.

> 

> > +		break;

> > +	default:

> > +		dev_err(ec->dev,

> > +			"Netronix embedded controller version %04x is not supported.\n",

> > +			version);

> > +		return -ENODEV;

> > +	}

> 

> Applied, thanks.


Sorry, that should have been:

For my own reference (apply this as-is to your sign-off block):

  Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
J. Neuschäfer Dec. 2, 2020, 2 p.m. UTC | #3
On Wed, Dec 02, 2020 at 01:05:20PM +0000, Lee Jones wrote:
> On Sun, 22 Nov 2020, Jonathan Neuschäfer wrote:

[...]
> > +	/* Bail out if we encounter an unknown firmware version */

> > +	switch (version) {

> > +	case 0xd726: /* found in Kobo Aura */

> 

> No magic numbers.

> 

> Please submit a subsequent patch to define this.


Will do.

But I don't think I'll be able to give it a more meaningful name than
NTXEC_VERSION_D726. I don't have a good overview of which versions
appear in which devices. "0xd726 found in Kobo Aura" only means that;
I don't know if it's the only version used in the Kobo Aura, and I don't
know if the Kobo Aura is the only device where it is used.


Thanks,
Jonathan Neuschäfer
Lee Jones Dec. 2, 2020, 3:09 p.m. UTC | #4
On Wed, 02 Dec 2020, Jonathan Neuschäfer wrote:

> On Wed, Dec 02, 2020 at 01:05:20PM +0000, Lee Jones wrote:

> > On Sun, 22 Nov 2020, Jonathan Neuschäfer wrote:

> [...]

> > > +	/* Bail out if we encounter an unknown firmware version */

> > > +	switch (version) {

> > > +	case 0xd726: /* found in Kobo Aura */

> > 

> > No magic numbers.

> > 

> > Please submit a subsequent patch to define this.

> 

> Will do.

> 

> But I don't think I'll be able to give it a more meaningful name than

> NTXEC_VERSION_D726. I don't have a good overview of which versions

> appear in which devices. "0xd726 found in Kobo Aura" only means that;

> I don't know if it's the only version used in the Kobo Aura, and I don't

> know if the Kobo Aura is the only device where it is used.


Defines are not set in stone.

They can evolve over time as more is known.

NTXEC_KOBO_AURA would be fine for now.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
J. Neuschäfer Dec. 2, 2020, 5:11 p.m. UTC | #5
On Wed, Dec 02, 2020 at 03:09:43PM +0000, Lee Jones wrote:
> On Wed, 02 Dec 2020, Jonathan Neuschäfer wrote:

> 

> > On Wed, Dec 02, 2020 at 01:05:20PM +0000, Lee Jones wrote:

> > > On Sun, 22 Nov 2020, Jonathan Neuschäfer wrote:

> > [...]

> > > > +	/* Bail out if we encounter an unknown firmware version */

> > > > +	switch (version) {

> > > > +	case 0xd726: /* found in Kobo Aura */

> > > 

> > > No magic numbers.

> > > 

> > > Please submit a subsequent patch to define this.

> > 

> > Will do.

> > 

> > But I don't think I'll be able to give it a more meaningful name than

> > NTXEC_VERSION_D726. I don't have a good overview of which versions

> > appear in which devices. "0xd726 found in Kobo Aura" only means that;

> > I don't know if it's the only version used in the Kobo Aura, and I don't

> > know if the Kobo Aura is the only device where it is used.

> 

> Defines are not set in stone.

> 

> They can evolve over time as more is known.

> 

> NTXEC_KOBO_AURA would be fine for now.


Alright.


Thanks,
Jonathan Neuschäfer
diff mbox series

Patch

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 8b99a13669bfc..d96751f884dc6 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -990,6 +990,17 @@  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 1780019d24748..815c99b84019e 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -218,6 +218,7 @@  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..c1510711d7363
--- /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 <j.neuschaefer@gmx.net>
+ */
+
+#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 0xd726: /* found in 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..b1de91f4fdcad
--- /dev/null
+++ b/include/linux/mfd/ntxec.h
@@ -0,0 +1,34 @@ 
+/* 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;
+}
+
+#endif