From: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx> Add a software PWM which toggles a GPIO from a high-resolution timer. This will naturally not be as accurate or as efficient as a hardware PWM, but it is useful in some cases. I have for example used it for evaluating LED brightness handling (via leds-pwm) on a board where the LED was just hooked up to a GPIO, and for a simple verification of the timer frequency on another platform. Since high-resolution timers are used, sleeping gpio chips are not supported and are rejected in the probe function. Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx> Co-developed-by: Stefan Wahren <wahrenst@xxxxxxx> Signed-off-by: Stefan Wahren <wahrenst@xxxxxxx> --- drivers/pwm/Kconfig | 11 ++ drivers/pwm/Makefile | 1 + drivers/pwm/pwm-gpio.c | 221 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 233 insertions(+) create mode 100644 drivers/pwm/pwm-gpio.c diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig index 4b956d661755..7cfda2cde130 100644 --- a/drivers/pwm/Kconfig +++ b/drivers/pwm/Kconfig @@ -227,6 +227,17 @@ config PWM_FSL_FTM To compile this driver as a module, choose M here: the module will be called pwm-fsl-ftm. +config PWM_GPIO + tristate "GPIO PWM support" + depends on GPIOLIB + depends on HIGH_RES_TIMERS + help + Generic PWM framework driver for a software PWM toggling a GPIO pin + from kernel high-resolution timers. + + To compile this driver as a module, choose M here: the module + will be called pwm-gpio. + config PWM_HIBVT tristate "HiSilicon BVT PWM support" depends on ARCH_HISI || COMPILE_TEST diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile index c5ec9e168ee7..59d1a46bb1af 100644 --- a/drivers/pwm/Makefile +++ b/drivers/pwm/Makefile @@ -19,6 +19,7 @@ obj-$(CONFIG_PWM_DWC_CORE) += pwm-dwc-core.o obj-$(CONFIG_PWM_DWC) += pwm-dwc.o obj-$(CONFIG_PWM_EP93XX) += pwm-ep93xx.o obj-$(CONFIG_PWM_FSL_FTM) += pwm-fsl-ftm.o +obj-$(CONFIG_PWM_GPIO) += pwm-gpio.o obj-$(CONFIG_PWM_HIBVT) += pwm-hibvt.o obj-$(CONFIG_PWM_IMG) += pwm-img.o obj-$(CONFIG_PWM_IMX1) += pwm-imx1.o diff --git a/drivers/pwm/pwm-gpio.c b/drivers/pwm/pwm-gpio.c new file mode 100644 index 000000000000..14637abe465b --- /dev/null +++ b/drivers/pwm/pwm-gpio.c @@ -0,0 +1,221 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Generic software PWM for modulating GPIOs + * + * Copyright (C) 2020 Axis Communications AB + * Copyright (C) 2020 Nicola Di Lieto + * Copyright (C) 2024 Stefan Wahren + */ + +#include <linux/device.h> +#include <linux/err.h> +#include <linux/gpio/consumer.h> +#include <linux/hrtimer.h> +#include <linux/module.h> +#include <linux/mod_devicetable.h> +#include <linux/platform_device.h> +#include <linux/pwm.h> +#include <linux/spinlock.h> + +struct pwm_gpio { + struct pwm_chip chip; + struct hrtimer gpio_timer; + struct gpio_desc *gpio; + struct pwm_state state; + struct pwm_state next_state; + + /* Protect internal state between pwm_ops and hrtimer */ + spinlock_t lock; + + bool changing; + bool running; + bool level; +}; + +static unsigned long pwm_gpio_toggle(struct pwm_gpio *gpwm, bool level) +{ + const struct pwm_state *state = &gpwm->state; + bool invert = state->polarity == PWM_POLARITY_INVERSED; + + gpwm->level = level; + gpiod_set_value(gpwm->gpio, gpwm->level ^ invert); + + if (!state->duty_cycle || state->duty_cycle == state->period) { + gpwm->running = false; + return 0; + } + + gpwm->running = true; + return level ? state->duty_cycle : state->period - state->duty_cycle; +} + +static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *gpio_timer) +{ + struct pwm_gpio *gpwm = container_of(gpio_timer, struct pwm_gpio, + gpio_timer); + unsigned long next_toggle; + unsigned long flags; + bool new_level; + + spin_lock_irqsave(&gpwm->lock, flags); + + /* Apply new state at end of current period */ + if (!gpwm->level && gpwm->changing) { + gpwm->changing = false; + gpwm->state = gpwm->next_state; + new_level = !!gpwm->state.duty_cycle; + } else { + new_level = !gpwm->level; + } + + next_toggle = pwm_gpio_toggle(gpwm, new_level); + if (next_toggle) { + hrtimer_forward(gpio_timer, hrtimer_get_expires(gpio_timer), + ns_to_ktime(next_toggle)); + } + + spin_unlock_irqrestore(&gpwm->lock, flags); + + return next_toggle ? HRTIMER_RESTART : HRTIMER_NORESTART; +} + +static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm, + const struct pwm_state *state) +{ + struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip); + bool invert = state->polarity == PWM_POLARITY_INVERSED; + unsigned long flags; + + if (!state->enabled) { + hrtimer_cancel(&gpwm->gpio_timer); + } else if (!gpwm->running) { + /* + * This just enables the output, but pwm_gpio_toggle() + * really starts the duty cycle. + */ + int ret = gpiod_direction_output(gpwm->gpio, invert); + + if (ret) + return ret; + } + + spin_lock_irqsave(&gpwm->lock, flags); + + if (!state->enabled) { + gpwm->state = *state; + gpwm->running = false; + gpwm->changing = false; + + gpiod_set_value(gpwm->gpio, invert); + } else if (gpwm->running) { + gpwm->next_state = *state; + gpwm->changing = true; + } else { + unsigned long next_toggle; + + gpwm->state = *state; + gpwm->changing = false; + + next_toggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle); + if (next_toggle) { + hrtimer_start(&gpwm->gpio_timer, next_toggle, + HRTIMER_MODE_REL); + } + } + + spin_unlock_irqrestore(&gpwm->lock, flags); + + return 0; +} + +static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm, + struct pwm_state *state) +{ + struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip); + unsigned long flags; + + spin_lock_irqsave(&gpwm->lock, flags); + + if (gpwm->changing) + *state = gpwm->next_state; + else + *state = gpwm->state; + + spin_unlock_irqrestore(&gpwm->lock, flags); + + return 0; +} + +static const struct pwm_ops pwm_gpio_ops = { + .apply = pwm_gpio_apply, + .get_state = pwm_gpio_get_state, +}; + +static int pwm_gpio_probe(struct platform_device *pdev) +{ + struct device *dev = &pdev->dev; + struct pwm_gpio *gpwm; + int ret; + + gpwm = devm_kzalloc(dev, sizeof(*gpwm), GFP_KERNEL); + if (!gpwm) + return -ENOMEM; + + spin_lock_init(&gpwm->lock); + + gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS); + if (IS_ERR(gpwm->gpio)) { + return dev_err_probe(dev, PTR_ERR(gpwm->gpio), + "could not get gpio\n"); + } + + if (gpiod_cansleep(gpwm->gpio)) { + return dev_err_probe(dev, -EINVAL, + "sleeping GPIO %d not supported\n", + desc_to_gpio(gpwm->gpio)); + } + + gpwm->chip.dev = dev; + gpwm->chip.ops = &pwm_gpio_ops; + gpwm->chip.npwm = 1; + + hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + gpwm->gpio_timer.function = pwm_gpio_timer; + + ret = pwmchip_add(&gpwm->chip); + if (ret < 0) + return dev_err_probe(dev, ret, "could not add pwmchip\n"); + + platform_set_drvdata(pdev, gpwm); + + return 0; +} + +static void pwm_gpio_remove(struct platform_device *pdev) +{ + struct pwm_gpio *gpwm = platform_get_drvdata(pdev); + + pwmchip_remove(&gpwm->chip); + hrtimer_cancel(&gpwm->gpio_timer); +} + +static const struct of_device_id pwm_gpio_dt_ids[] = { + { .compatible = "pwm-gpio" }, + { /* sentinel */ } +}; +MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids); + +static struct platform_driver pwm_gpio_driver = { + .driver = { + .name = "pwm-gpio", + .of_match_table = pwm_gpio_dt_ids, + }, + .probe = pwm_gpio_probe, + .remove_new = pwm_gpio_remove, +}; +module_platform_driver(pwm_gpio_driver); + +MODULE_DESCRIPTION("PWM GPIO driver"); +MODULE_ALIAS("platform:pwm-gpio"); +MODULE_AUTHOR("Vincent Whitchurch"); +MODULE_LICENSE("GPL"); -- 2.34.1