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@xxxxxxx> --- v3: - 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@xxxxxxx/ - 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 | 161 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 170 insertions(+) create mode 100644 drivers/pwm/pwm-ntxec.c diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig index 7dbcf6973d335..530dfda38d65e 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 ODM + 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 2c2ba0a035577..1cc50dba22d1b 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..50da2dc14bb03 --- /dev/null +++ b/drivers/pwm/pwm-ntxec.c @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * 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 PWM output. + * + * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@xxxxxxx> + */ + +#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_pwm(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 * 0x10000 - 1) + +static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev, + const struct pwm_state *state) +{ + struct ntxec_pwm *pwm = pwmchip_to_pwm(pwm_dev->chip); + unsigned int duty = state->duty_cycle; + unsigned int period = state->period; + int res = 0; + + if (period > MAX_PERIOD_NS) { + dev_warn(pwm->dev, + "Period is not representable in 16 bits after division by %u: %u\n", + TIME_BASE_NS, period); + return -ERANGE; + } + + period /= TIME_BASE_NS; + duty /= TIME_BASE_NS; + + res = regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8)); + if (res) + return res; + + res = regmap_write(pwm->ec->regmap, NTXEC_REG_PERIOD_LOW, ntxec_reg8(period)); + if (res) + return res; + + res = regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8)); + if (res) + return res; + + res = regmap_write(pwm->ec->regmap, NTXEC_REG_DUTY_LOW, ntxec_reg8(duty)); + if (res) + return res; + + /* + * Writing a duty cycle of zone 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(pwm->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1)); + if (res) + return res; + + /* Disable the auto-off timer */ + res = regmap_write(pwm->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff)); + if (res) + return res; + + return regmap_write(pwm->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff)); + } else { + return regmap_write(pwm->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0)); + } +} + +static struct pwm_ops ntxec_pwm_ops = { + .apply = ntxec_pwm_apply, + .owner = THIS_MODULE, +}; + +static int ntxec_pwm_probe(struct platform_device *pdev) +{ + struct ntxec *ec = dev_get_drvdata(pdev->dev.parent); + struct ntxec_pwm *pwm; + struct pwm_chip *chip; + int res; + + pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL); + if (!pwm) + return -ENOMEM; + + pwm->ec = ec; + pwm->dev = &pdev->dev; + + chip = &pwm->chip; + chip->dev = &pdev->dev; + chip->ops = &ntxec_pwm_ops; + chip->base = -1; + chip->npwm = 1; + + res = pwmchip_add(chip); + if (res < 0) + return res; + + platform_set_drvdata(pdev, pwm); + + return 0; +} + +static int ntxec_pwm_remove(struct platform_device *pdev) +{ + struct ntxec_pwm *pwm = platform_get_drvdata(pdev); + struct pwm_chip *chip = &pwm->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@xxxxxxx>"); +MODULE_DESCRIPTION("PWM driver for Netronix EC"); +MODULE_LICENSE("GPL"); -- 2.28.0
