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> --- While preparing this driver for posting, I found a pwm-gpio driver posted to the lists way back in 2015 by Olliver Schinagl: https://lore.kernel.org/linux-pwm/1445895161-2317-8-git-send-email-o.schinagl@xxxxxxxxxxxxx/ This driver was developed independently, but since both drivers are trivial they are quite similar. The main difference I see (apart from the usage of newer APIs and DT schemas) is that this driver only supports one PWM per instance, which makes for simpler code. I also reject sleeping GPIO chips explicitly while that driver uses gpio_set_value_cansleep() from a hrtimer, which is a no-no. drivers/pwm/Kconfig | 10 ++++ drivers/pwm/Makefile | 1 + drivers/pwm/pwm-gpio.c | 123 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 134 insertions(+) create mode 100644 drivers/pwm/pwm-gpio.c diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig index 7dbcf6973d33..20e4fda82e61 100644 --- a/drivers/pwm/Kconfig +++ b/drivers/pwm/Kconfig @@ -181,6 +181,16 @@ 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 OF && GPIOLIB + 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 2c2ba0a03557..2e045f063cd1 100644 --- a/drivers/pwm/Makefile +++ b/drivers/pwm/Makefile @@ -15,6 +15,7 @@ obj-$(CONFIG_PWM_CRC) += pwm-crc.o obj-$(CONFIG_PWM_CROS_EC) += pwm-cros-ec.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..e579aca0f937 --- /dev/null +++ b/drivers/pwm/pwm-gpio.c @@ -0,0 +1,123 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (C) 2020 Axis Communications AB */ + +#include <linux/gpio/consumer.h> +#include <linux/platform_device.h> +#include <linux/hrtimer.h> +#include <linux/module.h> +#include <linux/slab.h> +#include <linux/pwm.h> +#include <linux/err.h> +#include <linux/of.h> + +struct pwm_gpio { + struct pwm_chip chip; + struct hrtimer hrtimer; + struct gpio_desc *gpio; + ktime_t on_interval; + ktime_t off_interval; + bool invert; + bool on; +}; + +static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *hrtimer) +{ + struct pwm_gpio *gpwm = container_of(hrtimer, struct pwm_gpio, hrtimer); + bool newon = !gpwm->on; + + gpwm->on = newon; + gpiod_set_value(gpwm->gpio, newon ^ gpwm->invert); + + hrtimer_forward_now(hrtimer, newon ? gpwm->on_interval : gpwm->off_interval); + + return HRTIMER_RESTART; +} + +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); + + hrtimer_cancel(&gpwm->hrtimer); + + if (!state->enabled) { + gpiod_set_value(gpwm->gpio, 0); + return 0; + } + + gpwm->on_interval = ns_to_ktime(state->duty_cycle); + gpwm->off_interval = ns_to_ktime(state->period - state->duty_cycle); + gpwm->invert = state->polarity == PWM_POLARITY_INVERSED; + + gpwm->on = !!gpwm->on_interval; + gpiod_set_value(gpwm->gpio, gpwm->on ^ gpwm->invert); + + if (gpwm->on_interval && gpwm->off_interval) + hrtimer_start(&gpwm->hrtimer, gpwm->on_interval, HRTIMER_MODE_REL); + + return 0; +} + +static const struct pwm_ops pwm_gpio_ops = { + .owner = THIS_MODULE, + .apply = pwm_gpio_apply, +}; + +static int pwm_gpio_probe(struct platform_device *pdev) +{ + struct pwm_gpio *gpwm; + int ret; + + gpwm = devm_kzalloc(&pdev->dev, sizeof(*gpwm), GFP_KERNEL); + if (!gpwm) + return -ENOMEM; + + gpwm->gpio = devm_gpiod_get(&pdev->dev, NULL, GPIOD_OUT_LOW); + if (IS_ERR(gpwm->gpio)) + return PTR_ERR(gpwm->gpio); + + if (gpiod_cansleep(gpwm->gpio)) + return -EINVAL; + + gpwm->chip.dev = &pdev->dev; + gpwm->chip.ops = &pwm_gpio_ops; + gpwm->chip.base = pdev->id; + gpwm->chip.npwm = 1; + + hrtimer_init(&gpwm->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + gpwm->hrtimer.function = pwm_gpio_timer; + + ret = pwmchip_add(&gpwm->chip); + if (ret < 0) + return ret; + + platform_set_drvdata(pdev, gpwm); + + return 0; +} + +static int pwm_gpio_remove(struct platform_device *pdev) +{ + struct pwm_gpio *gpwm = platform_get_drvdata(pdev); + + return pwmchip_remove(&gpwm->chip); +} + +static const struct of_device_id pwm_gpio_dt_ids[] = { + { .compatible = "pwm-gpio", }, + { } +}; +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 = pwm_gpio_remove, +}; + +module_platform_driver(pwm_gpio_driver); + +MODULE_LICENSE("GPL v2"); -- 2.25.1
