diff mbox series

[v7,4/7] pwm: ntxec: Add driver for PWM function in Netronix EC

Message ID 20210109180220.121511-5-j.neuschaefer@gmx.net
State Superseded
Headers show
Series Netronix embedded controller driver for Kobo and Tolino ebook readers | expand

Commit Message

J. Neuschäfer Jan. 9, 2021, 6:02 p.m. UTC
The Netronix EC provides a PWM output which is used for the backlight
on some ebook readers. This patches adds a driver for the PWM output.

The .get_state callback is not implemented, because the PWM state can't
be read back from the hardware.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
---
v7:
- no changes

v6:
- https://lore.kernel.org/lkml/20201208011000.3060239-5-j.neuschaefer@gmx.net/
- Move period / duty cycle setting code to a function
- Rename pwmchip_to_priv to ntxec_pwm_from_chip
- Set period and duty cycle only before enabling the output
- Mention that duty=0, enable=1 is assumed not to happen
- Interleave writes to the period and duty cycle registers, to minimize the
  window of time that an inconsistent state is configured

v5:
- https://lore.kernel.org/lkml/20201201011513.1627028-5-j.neuschaefer@gmx.net/
- Avoid truncation of period and duty cycle to 32 bits
- Make ntxec_pwm_ops const
- Use regmap_multi_reg_write
- Add comment about get_state to ntxec_pwm_ops
- Add comments about non-atomicity of (period, duty cycle) update

v4:
- https://lore.kernel.org/lkml/20201122222739.1455132-5-j.neuschaefer@gmx.net/
- Document hardware/driver limitations
- Only accept normal polarity
- Fix a typo ("zone" -> "zero")
- change MAX_PERIOD_NS to 0xffff * 125
- Clamp period to the maximum rather than returning an error
- Rename private struct pointer to priv
- Rearrage control flow in _probe to save a few lines and a temporary variable
- Add missing MODULE_ALIAS line
- Spell out ODM

v3:
- https://lore.kernel.org/lkml/20200924192455.2484005-5-j.neuschaefer@gmx.net/
- Relicense as GPLv2 or later
- Add email address to copyright line
- Remove OF compatible string and don't include linux/of_device.h
- Fix bogus ?: in return line
- Don't use a comma after sentinels
- Avoid ret |= ... pattern
- Move 8-bit register conversion to ntxec.h

v2:
- https://lore.kernel.org/lkml/20200905133230.1014581-6-j.neuschaefer@gmx.net/
- Various grammar and style improvements, as suggested by Uwe Kleine-König,
  Lee Jones, and Alexandre Belloni
- Switch to regmap
- Prefix registers with NTXEC_REG_
- Add help text to the Kconfig option
- Use the .apply callback instead of the old API
- Add a #define for the time base (125ns)
- Don't change device state in .probe; this avoids multiple problems
- Rework division and overflow check logic to perform divisions in 32 bits
- Avoid setting duty cycle to zero, to work around a hardware quirk
---
 drivers/pwm/Kconfig     |   8 ++
 drivers/pwm/Makefile    |   1 +
 drivers/pwm/pwm-ntxec.c | 182 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 191 insertions(+)
 create mode 100644 drivers/pwm/pwm-ntxec.c

--
2.29.2

Comments

Uwe Kleine-König Jan. 11, 2021, 9:13 a.m. UTC | #1
Hello,

On Sat, Jan 09, 2021 at 07:02:17PM +0100, Jonathan Neuschäfer wrote:
> The Netronix EC provides a PWM output which is used for the backlight

> on some ebook readers. This patches adds a driver for the PWM output.

> 

> The .get_state callback is not implemented, because the PWM state can't

> be read back from the hardware.


There is only very little I would have done differently (only indention
which is too minor to make a fuss), so:

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

 
Thanks for your work
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
Thierry Reding Jan. 11, 2021, 12:53 p.m. UTC | #2
On Sat, Jan 09, 2021 at 07:02:17PM +0100, Jonathan Neuschäfer wrote:
> The Netronix EC provides a PWM output which is used for the backlight

> on some ebook readers. This patches adds a driver for the PWM output.

> 

> The .get_state callback is not implemented, because the PWM state can't

> be read back from the hardware.

> 

> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

> ---

> v7:

> - no changes

> 

> v6:

> - https://lore.kernel.org/lkml/20201208011000.3060239-5-j.neuschaefer@gmx.net/

> - Move period / duty cycle setting code to a function

> - Rename pwmchip_to_priv to ntxec_pwm_from_chip

> - Set period and duty cycle only before enabling the output

> - Mention that duty=0, enable=1 is assumed not to happen

> - Interleave writes to the period and duty cycle registers, to minimize the

>   window of time that an inconsistent state is configured

> 

> v5:

> - https://lore.kernel.org/lkml/20201201011513.1627028-5-j.neuschaefer@gmx.net/

> - Avoid truncation of period and duty cycle to 32 bits

> - Make ntxec_pwm_ops const

> - Use regmap_multi_reg_write

> - Add comment about get_state to ntxec_pwm_ops

> - Add comments about non-atomicity of (period, duty cycle) update

> 

> v4:

> - https://lore.kernel.org/lkml/20201122222739.1455132-5-j.neuschaefer@gmx.net/

> - Document hardware/driver limitations

> - Only accept normal polarity

> - Fix a typo ("zone" -> "zero")

> - change MAX_PERIOD_NS to 0xffff * 125

> - Clamp period to the maximum rather than returning an error

> - Rename private struct pointer to priv

> - Rearrage control flow in _probe to save a few lines and a temporary variable

> - Add missing MODULE_ALIAS line

> - Spell out ODM

> 

> v3:

> - https://lore.kernel.org/lkml/20200924192455.2484005-5-j.neuschaefer@gmx.net/

> - Relicense as GPLv2 or later

> - Add email address to copyright line

> - Remove OF compatible string and don't include linux/of_device.h

> - Fix bogus ?: in return line

> - Don't use a comma after sentinels

> - Avoid ret |= ... pattern

> - Move 8-bit register conversion to ntxec.h

> 

> v2:

> - https://lore.kernel.org/lkml/20200905133230.1014581-6-j.neuschaefer@gmx.net/

> - Various grammar and style improvements, as suggested by Uwe Kleine-König,

>   Lee Jones, and Alexandre Belloni

> - Switch to regmap

> - Prefix registers with NTXEC_REG_

> - Add help text to the Kconfig option

> - Use the .apply callback instead of the old API

> - Add a #define for the time base (125ns)

> - Don't change device state in .probe; this avoids multiple problems

> - Rework division and overflow check logic to perform divisions in 32 bits

> - Avoid setting duty cycle to zero, to work around a hardware quirk

> ---

>  drivers/pwm/Kconfig     |   8 ++

>  drivers/pwm/Makefile    |   1 +

>  drivers/pwm/pwm-ntxec.c | 182 ++++++++++++++++++++++++++++++++++++++++

>  3 files changed, 191 insertions(+)

>  create mode 100644 drivers/pwm/pwm-ntxec.c


Lee, I assume you'll want to pick the whole set up into the MFD tree? If
so:

Acked-by: Thierry Reding <thierry.reding@gmail.com>
Lee Jones Jan. 11, 2021, 4:42 p.m. UTC | #3
On Mon, 11 Jan 2021, Thierry Reding wrote:

> On Sat, Jan 09, 2021 at 07:02:17PM +0100, Jonathan Neuschäfer wrote:

> > The Netronix EC provides a PWM output which is used for the backlight

> > on some ebook readers. This patches adds a driver for the PWM output.

> > 

> > The .get_state callback is not implemented, because the PWM state can't

> > be read back from the hardware.

> > 

> > Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

> > ---

> > v7:

> > - no changes

> > 

> > v6:

> > - https://lore.kernel.org/lkml/20201208011000.3060239-5-j.neuschaefer@gmx.net/

> > - Move period / duty cycle setting code to a function

> > - Rename pwmchip_to_priv to ntxec_pwm_from_chip

> > - Set period and duty cycle only before enabling the output

> > - Mention that duty=0, enable=1 is assumed not to happen

> > - Interleave writes to the period and duty cycle registers, to minimize the

> >   window of time that an inconsistent state is configured

> > 

> > v5:

> > - https://lore.kernel.org/lkml/20201201011513.1627028-5-j.neuschaefer@gmx.net/

> > - Avoid truncation of period and duty cycle to 32 bits

> > - Make ntxec_pwm_ops const

> > - Use regmap_multi_reg_write

> > - Add comment about get_state to ntxec_pwm_ops

> > - Add comments about non-atomicity of (period, duty cycle) update

> > 

> > v4:

> > - https://lore.kernel.org/lkml/20201122222739.1455132-5-j.neuschaefer@gmx.net/

> > - Document hardware/driver limitations

> > - Only accept normal polarity

> > - Fix a typo ("zone" -> "zero")

> > - change MAX_PERIOD_NS to 0xffff * 125

> > - Clamp period to the maximum rather than returning an error

> > - Rename private struct pointer to priv

> > - Rearrage control flow in _probe to save a few lines and a temporary variable

> > - Add missing MODULE_ALIAS line

> > - Spell out ODM

> > 

> > v3:

> > - https://lore.kernel.org/lkml/20200924192455.2484005-5-j.neuschaefer@gmx.net/

> > - Relicense as GPLv2 or later

> > - Add email address to copyright line

> > - Remove OF compatible string and don't include linux/of_device.h

> > - Fix bogus ?: in return line

> > - Don't use a comma after sentinels

> > - Avoid ret |= ... pattern

> > - Move 8-bit register conversion to ntxec.h

> > 

> > v2:

> > - https://lore.kernel.org/lkml/20200905133230.1014581-6-j.neuschaefer@gmx.net/

> > - Various grammar and style improvements, as suggested by Uwe Kleine-König,

> >   Lee Jones, and Alexandre Belloni

> > - Switch to regmap

> > - Prefix registers with NTXEC_REG_

> > - Add help text to the Kconfig option

> > - Use the .apply callback instead of the old API

> > - Add a #define for the time base (125ns)

> > - Don't change device state in .probe; this avoids multiple problems

> > - Rework division and overflow check logic to perform divisions in 32 bits

> > - Avoid setting duty cycle to zero, to work around a hardware quirk

> > ---

> >  drivers/pwm/Kconfig     |   8 ++

> >  drivers/pwm/Makefile    |   1 +

> >  drivers/pwm/pwm-ntxec.c | 182 ++++++++++++++++++++++++++++++++++++++++

> >  3 files changed, 191 insertions(+)

> >  create mode 100644 drivers/pwm/pwm-ntxec.c

> 

> Lee, I assume you'll want to pick the whole set up into the MFD tree? If

> so:


Yes, I'll pick this up once we have all the Acks.

The Arm parts usually go in separately.

> Acked-by: Thierry Reding <thierry.reding@gmail.com>


Thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
Andreas Kemnade Jan. 12, 2021, 7:39 p.m. UTC | #4
On Sat,  9 Jan 2021 19:02:17 +0100
Jonathan Neuschäfer <j.neuschaefer@gmx.net> wrote:

> The Netronix EC provides a PWM output which is used for the backlight

> on some ebook readers. This patches adds a driver for the PWM output.

> 

> The .get_state callback is not implemented, because the PWM state can't

> be read back from the hardware.

> 

> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

> ---

> v7:

> - no changes

> 

> v6:

> - https://lore.kernel.org/lkml/20201208011000.3060239-5-j.neuschaefer@gmx.net/

> - Move period / duty cycle setting code to a function

> - Rename pwmchip_to_priv to ntxec_pwm_from_chip

> - Set period and duty cycle only before enabling the output

> - Mention that duty=0, enable=1 is assumed not to happen

> - Interleave writes to the period and duty cycle registers, to minimize the

>   window of time that an inconsistent state is configured

> 

> v5:

> - https://lore.kernel.org/lkml/20201201011513.1627028-5-j.neuschaefer@gmx.net/

> - Avoid truncation of period and duty cycle to 32 bits

> - Make ntxec_pwm_ops const

> - Use regmap_multi_reg_write

> - Add comment about get_state to ntxec_pwm_ops

> - Add comments about non-atomicity of (period, duty cycle) update

> 

> v4:

> - https://lore.kernel.org/lkml/20201122222739.1455132-5-j.neuschaefer@gmx.net/

> - Document hardware/driver limitations

> - Only accept normal polarity

> - Fix a typo ("zone" -> "zero")

> - change MAX_PERIOD_NS to 0xffff * 125

> - Clamp period to the maximum rather than returning an error

> - Rename private struct pointer to priv

> - Rearrage control flow in _probe to save a few lines and a temporary variable

> - Add missing MODULE_ALIAS line

> - Spell out ODM

> 

> v3:

> - https://lore.kernel.org/lkml/20200924192455.2484005-5-j.neuschaefer@gmx.net/

> - Relicense as GPLv2 or later

> - Add email address to copyright line

> - Remove OF compatible string and don't include linux/of_device.h

> - Fix bogus ?: in return line

> - Don't use a comma after sentinels

> - Avoid ret |= ... pattern

> - Move 8-bit register conversion to ntxec.h

> 

> v2:

> - https://lore.kernel.org/lkml/20200905133230.1014581-6-j.neuschaefer@gmx.net/

> - Various grammar and style improvements, as suggested by Uwe Kleine-König,

>   Lee Jones, and Alexandre Belloni

> - Switch to regmap

> - Prefix registers with NTXEC_REG_

> - Add help text to the Kconfig option

> - Use the .apply callback instead of the old API

> - Add a #define for the time base (125ns)

> - Don't change device state in .probe; this avoids multiple problems

> - Rework division and overflow check logic to perform divisions in 32 bits

> - Avoid setting duty cycle to zero, to work around a hardware quirk

> ---

>  drivers/pwm/Kconfig     |   8 ++

>  drivers/pwm/Makefile    |   1 +

>  drivers/pwm/pwm-ntxec.c | 182 ++++++++++++++++++++++++++++++++++++++++

>  3 files changed, 191 insertions(+)

>  create mode 100644 drivers/pwm/pwm-ntxec.c

> 

> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig

> index 0937e1c047acb..a2830b8832b97 100644

> --- a/drivers/pwm/Kconfig

> +++ b/drivers/pwm/Kconfig

> @@ -393,6 +393,14 @@ config PWM_MXS

>  	  To compile this driver as a module, choose M here: the module

>  	  will be called pwm-mxs.

> 

> +config PWM_NTXEC

> +	tristate "Netronix embedded controller PWM support"

> +	depends on MFD_NTXEC

> +	help

> +	  Say yes here if you want to support the PWM output of the embedded

> +	  controller found in certain e-book readers designed by the original

> +	  design manufacturer Netronix.

> +

>  config PWM_OMAP_DMTIMER

>  	tristate "OMAP Dual-Mode Timer PWM support"

>  	depends on OF

> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile

> index 18b89d7fd092a..7d97eb595bbef 100644

> --- a/drivers/pwm/Makefile

> +++ b/drivers/pwm/Makefile

> @@ -35,6 +35,7 @@ obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o

>  obj-$(CONFIG_PWM_MEDIATEK)	+= pwm-mediatek.o

>  obj-$(CONFIG_PWM_MTK_DISP)	+= pwm-mtk-disp.o

>  obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o

> +obj-$(CONFIG_PWM_NTXEC)		+= pwm-ntxec.o

>  obj-$(CONFIG_PWM_OMAP_DMTIMER)	+= pwm-omap-dmtimer.o

>  obj-$(CONFIG_PWM_PCA9685)	+= pwm-pca9685.o

>  obj-$(CONFIG_PWM_PXA)		+= pwm-pxa.o

> diff --git a/drivers/pwm/pwm-ntxec.c b/drivers/pwm/pwm-ntxec.c

> new file mode 100644

> index 0000000000000..1db30a6caa3ad

> --- /dev/null

> +++ b/drivers/pwm/pwm-ntxec.c

> @@ -0,0 +1,182 @@

> +// 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 PWM output.

> + *

> + * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>

> + *

> + * Limitations:

> + * - The get_state callback is not implemented, because the current state of

> + *   the PWM output can't be read back from the hardware.

> + * - The hardware can only generate normal polarity output.

> + * - The period and duty cycle can't be changed together in one atomic action.

> + */

> +

> +#include <linux/mfd/ntxec.h>

> +#include <linux/module.h>

> +#include <linux/platform_device.h>

> +#include <linux/pwm.h>

> +#include <linux/regmap.h>

> +#include <linux/types.h>

> +

> +struct ntxec_pwm {

> +	struct device *dev;

> +	struct ntxec *ec;

> +	struct pwm_chip chip;

> +};

> +

> +static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip)

> +{

> +	return container_of(chip, struct ntxec_pwm, chip);

> +}

> +

> +#define NTXEC_REG_AUTO_OFF_HI	0xa1

> +#define NTXEC_REG_AUTO_OFF_LO	0xa2

> +#define NTXEC_REG_ENABLE	0xa3

> +#define NTXEC_REG_PERIOD_LOW	0xa4

> +#define NTXEC_REG_PERIOD_HIGH	0xa5

> +#define NTXEC_REG_DUTY_LOW	0xa6

> +#define NTXEC_REG_DUTY_HIGH	0xa7

> +

> +/*

> + * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are

> + * measured in this unit.

> + */

> +#define TIME_BASE_NS 125

> +

> +/*

> + * The maximum input value (in nanoseconds) is determined by the time base and

> + * the range of the hardware registers that hold the converted value.

> + * It fits into 32 bits, so we can do our calculations in 32 bits as well.

> + */

> +#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff)

> +

> +static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip,

> +						   int period, int duty)

> +{

> +	struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);

> +

> +	/*

> +	 * Changes to the period and duty cycle take effect as soon as the

> +	 * corresponding low byte is written, so the hardware may be configured

> +	 * to an inconsistent state after the period is written and before the

> +	 * duty cycle is fully written. If, in such a case, the old duty cycle

> +	 * is longer than the new period, the EC may output 100% for a moment.

> +	 *

> +	 * To minimize the time between the changes to period and duty cycle

> +	 * taking effect, the writes are interleaved.

> +	 */

> +

> +	struct reg_sequence regs[] = {

> +		{ NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) },

> +		{ NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) },

> +		{ NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) },

> +		{ NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) },

> +	};

> +

> +	return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs));

> +}

> +

> +static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,

> +			   const struct pwm_state *state)

> +{

> +	struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);

> +	unsigned int period, duty;

> +	int res;

> +

> +	if (state->polarity != PWM_POLARITY_NORMAL)

> +		return -EINVAL;

> +

> +	period = min_t(u64, state->period, MAX_PERIOD_NS);

> +	duty   = min_t(u64, state->duty_cycle, period);

> +

> +	period /= TIME_BASE_NS;

> +	duty   /= TIME_BASE_NS;

> +

> +	/*

> +	 * Writing a duty cycle of zero puts the device into a state where

> +	 * writing a higher duty cycle doesn't result in the brightness that it

> +	 * usually results in. This can be fixed by cycling the ENABLE register.

> +	 *

> +	 * As a workaround, write ENABLE=0 when the duty cycle is zero.

> +	 * The case that something has previously set the duty cycle to zero

> +	 * but ENABLE=1, is not handled.

> +	 */

> +	if (state->enabled && duty != 0) {

> +		res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty);

> +		if (res)

> +			return res;

> +

> +		res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1));

> +		if (res)

> +			return res;

> +

> +		/* Disable the auto-off timer */

> +		res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff));

> +		if (res)

> +			return res;

> +

> +		return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff));

> +	} else {

> +		return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0));

> +	}

> +}

> +

> +static const struct pwm_ops ntxec_pwm_ops = {

> +	.owner = THIS_MODULE,

> +	.apply = ntxec_pwm_apply,

> +	/*

> +	 * No .get_state callback, because the current state cannot be read

> +	 * back from the hardware.

> +	 */

> +};

> +

> +static int ntxec_pwm_probe(struct platform_device *pdev)

> +{

> +	struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);

> +	struct ntxec_pwm *priv;

> +	struct pwm_chip *chip;

> +

> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);

> +	if (!priv)

> +		return -ENOMEM;

> +

> +	priv->ec = ec;

> +	priv->dev = &pdev->dev;

> +

> +	platform_set_drvdata(pdev, priv);

> +

> +	chip = &priv->chip;

> +	chip->dev = &pdev->dev;


Hmm, I needed
chip->dev = &pdev->dev.parent to use the backlight example
in patch 2/7.
Not sure what the correct solution is. Maybe the pwm deserves its own
devicetree node.

Regards,
Andreas
Andreas Kemnade Jan. 13, 2021, 10:46 p.m. UTC | #5
On Tue, 12 Jan 2021 20:39:02 +0100
Andreas Kemnade <andreas@kemnade.info> wrote:

[...]
> > +static int ntxec_pwm_probe(struct platform_device *pdev)

> > +{

> > +	struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);

> > +	struct ntxec_pwm *priv;

> > +	struct pwm_chip *chip;

> > +

> > +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);

> > +	if (!priv)

> > +		return -ENOMEM;

> > +

> > +	priv->ec = ec;

> > +	priv->dev = &pdev->dev;

> > +

> > +	platform_set_drvdata(pdev, priv);

> > +

> > +	chip = &priv->chip;

> > +	chip->dev = &pdev->dev;  

> 

> Hmm, I needed

> chip->dev = &pdev->dev.parent to use the backlight example

> in patch 2/7.

> Not sure what the correct solution is. Maybe the pwm deserves its own

> devicetree node.

> 

probably just assigning the node from the parent.

   pdev->dev.of_node = pdev->dev.parent->of_node;

Regards,
Andreas
J. Neuschäfer Jan. 14, 2021, 10:31 p.m. UTC | #6
On Wed, Jan 13, 2021 at 11:46:45PM +0100, Andreas Kemnade wrote:
> On Tue, 12 Jan 2021 20:39:02 +0100

> Andreas Kemnade <andreas@kemnade.info> wrote:

> 

> [...]

> > > +static int ntxec_pwm_probe(struct platform_device *pdev)

[...]
> > Hmm, I needed

> > chip->dev = &pdev->dev.parent to use the backlight example

> > in patch 2/7.

> > Not sure what the correct solution is. Maybe the pwm deserves its own

> > devicetree node.

> > 

> probably just assigning the node from the parent.

> 

>    pdev->dev.of_node = pdev->dev.parent->of_node;


Ah, good catch, thanks. This works, I'll add it to the next version.


Jonathan
diff mbox series

Patch

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 0937e1c047acb..a2830b8832b97 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -393,6 +393,14 @@  config PWM_MXS
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-mxs.

+config PWM_NTXEC
+	tristate "Netronix embedded controller PWM support"
+	depends on MFD_NTXEC
+	help
+	  Say yes here if you want to support the PWM output of the embedded
+	  controller found in certain e-book readers designed by the original
+	  design manufacturer Netronix.
+
 config PWM_OMAP_DMTIMER
 	tristate "OMAP Dual-Mode Timer PWM support"
 	depends on OF
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 18b89d7fd092a..7d97eb595bbef 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -35,6 +35,7 @@  obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
 obj-$(CONFIG_PWM_MEDIATEK)	+= pwm-mediatek.o
 obj-$(CONFIG_PWM_MTK_DISP)	+= pwm-mtk-disp.o
 obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
+obj-$(CONFIG_PWM_NTXEC)		+= pwm-ntxec.o
 obj-$(CONFIG_PWM_OMAP_DMTIMER)	+= pwm-omap-dmtimer.o
 obj-$(CONFIG_PWM_PCA9685)	+= pwm-pca9685.o
 obj-$(CONFIG_PWM_PXA)		+= pwm-pxa.o
diff --git a/drivers/pwm/pwm-ntxec.c b/drivers/pwm/pwm-ntxec.c
new file mode 100644
index 0000000000000..1db30a6caa3ad
--- /dev/null
+++ b/drivers/pwm/pwm-ntxec.c
@@ -0,0 +1,182 @@ 
+// 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 PWM output.
+ *
+ * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>
+ *
+ * Limitations:
+ * - The get_state callback is not implemented, because the current state of
+ *   the PWM output can't be read back from the hardware.
+ * - The hardware can only generate normal polarity output.
+ * - The period and duty cycle can't be changed together in one atomic action.
+ */
+
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+struct ntxec_pwm {
+	struct device *dev;
+	struct ntxec *ec;
+	struct pwm_chip chip;
+};
+
+static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip)
+{
+	return container_of(chip, struct ntxec_pwm, chip);
+}
+
+#define NTXEC_REG_AUTO_OFF_HI	0xa1
+#define NTXEC_REG_AUTO_OFF_LO	0xa2
+#define NTXEC_REG_ENABLE	0xa3
+#define NTXEC_REG_PERIOD_LOW	0xa4
+#define NTXEC_REG_PERIOD_HIGH	0xa5
+#define NTXEC_REG_DUTY_LOW	0xa6
+#define NTXEC_REG_DUTY_HIGH	0xa7
+
+/*
+ * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
+ * measured in this unit.
+ */
+#define TIME_BASE_NS 125
+
+/*
+ * The maximum input value (in nanoseconds) is determined by the time base and
+ * the range of the hardware registers that hold the converted value.
+ * It fits into 32 bits, so we can do our calculations in 32 bits as well.
+ */
+#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff)
+
+static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip,
+						   int period, int duty)
+{
+	struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
+
+	/*
+	 * Changes to the period and duty cycle take effect as soon as the
+	 * corresponding low byte is written, so the hardware may be configured
+	 * to an inconsistent state after the period is written and before the
+	 * duty cycle is fully written. If, in such a case, the old duty cycle
+	 * is longer than the new period, the EC may output 100% for a moment.
+	 *
+	 * To minimize the time between the changes to period and duty cycle
+	 * taking effect, the writes are interleaved.
+	 */
+
+	struct reg_sequence regs[] = {
+		{ NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) },
+		{ NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) },
+		{ NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) },
+		{ NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) },
+	};
+
+	return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs));
+}
+
+static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,
+			   const struct pwm_state *state)
+{
+	struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
+	unsigned int period, duty;
+	int res;
+
+	if (state->polarity != PWM_POLARITY_NORMAL)
+		return -EINVAL;
+
+	period = min_t(u64, state->period, MAX_PERIOD_NS);
+	duty   = min_t(u64, state->duty_cycle, period);
+
+	period /= TIME_BASE_NS;
+	duty   /= TIME_BASE_NS;
+
+	/*
+	 * Writing a duty cycle of zero puts the device into a state where
+	 * writing a higher duty cycle doesn't result in the brightness that it
+	 * usually results in. This can be fixed by cycling the ENABLE register.
+	 *
+	 * As a workaround, write ENABLE=0 when the duty cycle is zero.
+	 * The case that something has previously set the duty cycle to zero
+	 * but ENABLE=1, is not handled.
+	 */
+	if (state->enabled && duty != 0) {
+		res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty);
+		if (res)
+			return res;
+
+		res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1));
+		if (res)
+			return res;
+
+		/* Disable the auto-off timer */
+		res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff));
+		if (res)
+			return res;
+
+		return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff));
+	} else {
+		return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0));
+	}
+}
+
+static const struct pwm_ops ntxec_pwm_ops = {
+	.owner = THIS_MODULE,
+	.apply = ntxec_pwm_apply,
+	/*
+	 * No .get_state callback, because the current state cannot be read
+	 * back from the hardware.
+	 */
+};
+
+static int ntxec_pwm_probe(struct platform_device *pdev)
+{
+	struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);
+	struct ntxec_pwm *priv;
+	struct pwm_chip *chip;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->ec = ec;
+	priv->dev = &pdev->dev;
+
+	platform_set_drvdata(pdev, priv);
+
+	chip = &priv->chip;
+	chip->dev = &pdev->dev;
+	chip->ops = &ntxec_pwm_ops;
+	chip->base = -1;
+	chip->npwm = 1;
+
+	return pwmchip_add(chip);
+}
+
+static int ntxec_pwm_remove(struct platform_device *pdev)
+{
+	struct ntxec_pwm *priv = platform_get_drvdata(pdev);
+	struct pwm_chip *chip = &priv->chip;
+
+	return pwmchip_remove(chip);
+}
+
+static struct platform_driver ntxec_pwm_driver = {
+	.driver = {
+		.name = "ntxec-pwm",
+	},
+	.probe = ntxec_pwm_probe,
+	.remove = ntxec_pwm_remove,
+};
+module_platform_driver(ntxec_pwm_driver);
+
+MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
+MODULE_DESCRIPTION("PWM driver for Netronix EC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ntxec-pwm");