On Sat, 9 Jan 2021 19:02:17 +0100 Jonathan Neuschäfer <[email protected]> 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]> > --- > v7: > - no changes > > v6: > - https://lore.kernel.org/lkml/[email protected]/ > - 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/[email protected]/ > - 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/[email protected]/ > - 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 | 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 <[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. > + * - 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
