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>
---
drivers/pwm/Kconfig | 10 +++
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-gpio.c | 195 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 206 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..0c35c6fdcef5
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -0,0 +1,195 @@
+// 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/spinlock.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;
+ struct pwm_state state;
+ struct pwm_state nextstate;
+ 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 *hrtimer)
+{
+ struct pwm_gpio *gpwm = container_of(hrtimer, struct pwm_gpio, hrtimer);
+ unsigned long nexttoggle;
+ unsigned long flags;
+ bool newlevel;
+
+ 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->nextstate;
+ newlevel = !!gpwm->state.duty_cycle;
+ } else {
+ newlevel = !gpwm->level;
+ }
+
+ nexttoggle = pwm_gpio_toggle(gpwm, newlevel);
+ if (nexttoggle)
+ hrtimer_forward(hrtimer, hrtimer_get_expires(hrtimer),
+ ns_to_ktime(nexttoggle));
+
+ spin_unlock_irqrestore(&gpwm->lock, flags);
+
+ return nexttoggle ? 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);
+ unsigned long flags;
+
+ if (!state->enabled)
+ hrtimer_cancel(&gpwm->hrtimer);
+
+ spin_lock_irqsave(&gpwm->lock, flags);
+
+ if (!state->enabled) {
+ gpwm->state = *state;
+ gpwm->running = false;
+ gpwm->changing = false;
+
+ gpiod_set_value(gpwm->gpio, 0);
+ } else if (gpwm->running) {
+ gpwm->nextstate = *state;
+ gpwm->changing = true;
+ } else {
+ unsigned long nexttoggle;
+
+ gpwm->state = *state;
+ gpwm->changing = false;
+
+ nexttoggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle);
+ if (nexttoggle)
+ hrtimer_start(&gpwm->hrtimer, nexttoggle,
+ HRTIMER_MODE_REL);
+ }
+
+ spin_unlock_irqrestore(&gpwm->lock, flags);
+
+ return 0;
+}
+
+static void 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->nextstate;
+ else
+ *state = gpwm->state;
+
+ spin_unlock_irqrestore(&gpwm->lock, flags);
+}
+
+static const struct pwm_ops pwm_gpio_ops = {
+ .owner = THIS_MODULE,
+ .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_OUT_LOW);
+ 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 GPIOs not supported\n");
+
+ gpwm->chip.dev = 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 dev_err_probe(dev, ret,
+ "could not add pwmchip\n");
+
+ platform_set_drvdata(pdev, gpwm);
+
+ return 0;
+}
+
+static int pwm_gpio_remove(struct platform_device *pdev)
+{
+ struct pwm_gpio *gpwm = platform_get_drvdata(pdev);
+
+ pwm_disable(&gpwm->chip.pwms[0]);
+
+ 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");
--
2.28.0
