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>
Co-developed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
Documentation/driver-api/gpio/drivers-on-gpio.rst | 7 +-
drivers/pwm/Kconfig | 11 +
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-gpio.c | 243 ++++++++++++++++++++++
4 files changed, 261 insertions(+), 1 deletion(-)
diff --git a/Documentation/driver-api/gpio/drivers-on-gpio.rst b/Documentation/driver-api/gpio/drivers-on-gpio.rst
index af632d764ac6..95572d2a94ce 100644
--- a/Documentation/driver-api/gpio/drivers-on-gpio.rst
+++ b/Documentation/driver-api/gpio/drivers-on-gpio.rst
@@ -27,7 +27,12 @@ hardware descriptions such as device tree or ACPI:
to the lines for a more permanent solution of this type.
- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
- an external speaker connected to a GPIO line.
+ an external speaker connected to a GPIO line. (If the beep is controlled by
+ off/on, for an actual PWM waveform, see pwm-gpio below.)
+
+- pwm-gpio: drivers/pwm/pwm-gpio.c is used to toggle a GPIO with a high
+ resolution timer producing a PWM waveform on the GPIO line, as well as
+ Linux high resolution timers can do.
- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
external connector status, such as a headset line for an audio driver or an
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 1dd7921194f5..68ba28d52c4c 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -223,6 +223,17 @@ 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 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 90913519f11a..65d62cc41a8f 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -18,6 +18,7 @@ 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..32ae9bba87c3
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -0,0 +1,243 @@
+// 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
+ * Copyright (C) 2024 Linus Walleij
+ */
+
+#include <linux/cleanup.h>
+#include <linux/container_of.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/hrtimer.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/pwm.h>
+#include <linux/spinlock.h>
+#include <linux/time.h>
+#include <linux/types.h>
+
+struct pwm_gpio {
+ 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 void pwm_gpio_round(struct pwm_state *dest, const struct pwm_state *src)
+{
+ u64 dividend;
+ u32 remainder;
+
+ *dest = *src;
+
+ /* Round down to hrtimer resolution */
+ dividend = dest->period;
+ remainder = do_div(dividend, hrtimer_resolution);
+ dest->period -= remainder;
+
+ dividend = dest->duty_cycle;
+ remainder = do_div(dividend, hrtimer_resolution);
+ dest->duty_cycle -= remainder;
+}
+
+static u64 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);
+ u64 next_toggle;
+ bool new_level;
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ /* 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));
+
+ 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 = pwmchip_get_drvdata(chip);
+ bool invert = state->polarity == PWM_POLARITY_INVERSED;
+
+ if (state->duty_cycle && state->duty_cycle < hrtimer_resolution)
+ return -EINVAL;
+
+ if (state->duty_cycle != state->period &&
+ (state->period - state->duty_cycle < hrtimer_resolution))
+ return -EINVAL;
+
+ if (!state->enabled) {
+ hrtimer_cancel(&gpwm->gpio_timer);
+ } else if (!gpwm->running) {
+ int ret;
+
+ /*
+ * This just enables the output, but pwm_gpio_toggle()
+ * really starts the duty cycle.
+ */
+ ret = gpiod_direction_output(gpwm->gpio, invert);
+ if (ret)
+ return ret;
+ }
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ if (!state->enabled) {
+ pwm_gpio_round(&gpwm->state, state);
+ gpwm->running = false;
+ gpwm->changing = false;
+
+ gpiod_set_value(gpwm->gpio, invert);
+ } else if (gpwm->running) {
+ pwm_gpio_round(&gpwm->next_state, state);
+ gpwm->changing = true;
+ } else {
+ unsigned long next_toggle;
+
+ pwm_gpio_round(&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);
+ }
+
+ return 0;
+}
+
+static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ if (gpwm->changing)
+ *state = gpwm->next_state;
+ else
+ *state = gpwm->state;
+
+ return 0;
+}
+
+static const struct pwm_ops pwm_gpio_ops = {
+ .apply = pwm_gpio_apply,
+ .get_state = pwm_gpio_get_state,
+};
+
+static void pwm_gpio_disable_hrtimer(void *data)
+{
+ struct pwm_gpio *gpwm = data;
+
+ hrtimer_cancel(&gpwm->gpio_timer);
+}
+
+static int pwm_gpio_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct pwm_chip *chip;
+ struct pwm_gpio *gpwm;
+ int ret;
+
+ chip = devm_pwmchip_alloc(dev, 1, sizeof(*gpwm));
+ if (IS_ERR(chip))
+ return PTR_ERR(chip);
+
+ gpwm = pwmchip_get_drvdata(chip);
+
+ 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),
+ "%pfw: could not get gpio\n",
+ dev_fwnode(dev));
+
+ if (gpiod_cansleep(gpwm->gpio))
+ return dev_err_probe(dev, -EINVAL,
+ "%pfw: sleeping GPIO not supported\n",
+ dev_fwnode(dev));
+
+ chip->ops = &pwm_gpio_ops;
+ chip->atomic = true;
+
+ hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm);
+ if (ret)
+ return ret;
+
+ gpwm->gpio_timer.function = pwm_gpio_timer;
+
+ ret = pwmchip_add(chip);
+ if (ret < 0)
+ return dev_err_probe(dev, ret, "could not add pwmchip\n");
+
+ platform_set_drvdata(pdev, gpwm);
+
+ return 0;
+}
+
+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,
+};
+module_platform_driver(pwm_gpio_driver);
+
+MODULE_DESCRIPTION("PWM GPIO driver");
+MODULE_AUTHOR("Vincent Whitchurch");
+MODULE_LICENSE("GPL");
--
2.45.1
