Hello, On Sun, Nov 22, 2020 at 11:27:36PM +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 <[email protected]> > --- > > v4: > - 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/[email protected]/ > - 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/[email protected]/ > - 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 | 166 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 175 insertions(+) > create mode 100644 drivers/pwm/pwm-ntxec.c > > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig > index 63be5362fd3a5..815f329ed5b46 100644 > --- a/drivers/pwm/Kconfig > +++ b/drivers/pwm/Kconfig > @@ -350,6 +350,14 @@ 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 cbdcd55d69eef..1deb29e6ae8e5 100644 > --- a/drivers/pwm/Makefile > +++ b/drivers/pwm/Makefile > @@ -32,6 +32,7 @@ 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..4f4f736d71aba > --- /dev/null > +++ b/drivers/pwm/pwm-ntxec.c > @@ -0,0 +1,166 @@ > +// 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 <[email protected]> > + * > + * 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. > + */ > + > +#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 *pwmchip_to_priv(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_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev, > + const struct pwm_state *state) > +{ > + struct ntxec_pwm *priv = pwmchip_to_priv(pwm_dev->chip); > + unsigned int duty = state->duty_cycle; > + unsigned int period = state->period;
state->duty_cycle and state->period are u64, so you're losing
information here. Consider state->duty_cycle = 0x100000001 and
state->period = 0x200000001.
> + int res = 0;
> +
> + if (state->polarity != PWM_POLARITY_NORMAL)
> + return -EINVAL;
> +
> + if (period > MAX_PERIOD_NS) {
> + period = MAX_PERIOD_NS;
> +
> + if (duty > period)
> + duty = period;
> + }
> +
> + period /= TIME_BASE_NS;
> + duty /= TIME_BASE_NS;
> +
> + res = regmap_write(priv->ec->regmap, NTXEC_REG_PERIOD_HIGH,
> ntxec_reg8(period >> 8));
> + if (res)
> + return res;
I wonder if you can add some logic to the regmap in the mfd driver such
that ntxec_reg8 isn't necessary for all users.
> + res = regmap_write(priv->ec->regmap, NTXEC_REG_PERIOD_LOW,
> ntxec_reg8(period));
> + if (res)
> + return res;
> +
> + res = regmap_write(priv->ec->regmap, NTXEC_REG_DUTY_HIGH,
> ntxec_reg8(duty >> 8));
> + if (res)
> + return res;
> +
> + res = regmap_write(priv->ec->regmap, NTXEC_REG_DUTY_LOW,
> ntxec_reg8(duty));
> + if (res)
> + return res;
I think I already asked, but I don't remember the reply: What happens to
the output between these writes? A comment here about this would be
suitable.
> +
> + /*
> + * 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.
> + */
> + if (state->enabled && duty != 0) {
> + 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 struct pwm_ops ntxec_pwm_ops = {
This can be const.
> + .apply = ntxec_pwm_apply,
/*
* The current state cannot be read out, so there is no .get_state
* callback.
*/
Hmm, at least you could provice a .get_state() callback that reports the
setting that was actually implemented for in the last call to .apply()?
@Thierry: Do you have concerns here? Actually it would be more effective
to have a callback (like .apply()) that modfies its pwm_state
accordingly. (Some drivers did that in the past, but I changed that to
get an uniform behaviour in 71523d1812aca61e32e742e87ec064e3d8c615e1.)
The downside is that people have to understand that concept to properly
use it. I'm torn about the right approach.
> + .owner = THIS_MODULE,
> +};
> +
> +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 <[email protected]>");
> +MODULE_DESCRIPTION("PWM driver for Netronix EC");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:ntxec-pwm");
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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