new file mode 100644
@@ -0,0 +1,14 @@
+Generic GPIO bit-banged PWM driver
+
+Required properties:
+ - compatible: should be "pwm-gpio"
+ - pwm-gpio: gpio describing the used gpio, see the gpio
+ bindings for the used gpio driver.
+
+Example:
+#include <dt-bindings/gpio/gpio.h>
+
+ pwm: pwm@0 {
+ compatible = "pwm-gpio";
+ pwm-gpio = <&pio 7 1 GPIO_ACTIVE_LOW>;
+ };
@@ -195,6 +195,16 @@ 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 "Generic GPIO bit-banged PWM support"
+ depends on GPIOLIB
+ depends on PWM
+ help
+ Driver to generate soft PWM on GPIO pin.
+
+ 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
@@ -16,6 +16,7 @@ obj-$(CONFIG_PWM_CROS_EC) += pwm-cros-ec.o
obj-$(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
new file mode 100644
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2019 Angelo Compagnucci <angelo.compagnucci@gmail.com>
+ *
+ * pwm-gpio.c - driver for pwm output on gpio via high resolution timers.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/gpio/consumer.h>
+#include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/property.h>
+#include <linux/pwm.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/device.h>
+#include <linux/hrtimer.h>
+#include <linux/ktime.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+
+struct gpio_pwm_chip {
+ struct pwm_chip chip;
+};
+
+struct gpio_pwm_data {
+
+ bool is_running;
+ bool polarity;
+ bool pin_on;
+ unsigned int on_time;
+ unsigned int off_time;
+ struct mutex lock;
+ struct hrtimer timer;
+ struct gpio_desc *gpio_pwm;
+};
+
+static void gpio_pwm_off(struct gpio_pwm_data *gpio_data)
+{
+ gpiod_set_value_cansleep(gpio_data->gpio_pwm,
+ gpio_data->polarity ? 1 : 0);
+ gpio_data->pin_on = false;
+}
+
+static void gpio_pwm_on(struct gpio_pwm_data *gpio_data)
+{
+ gpiod_set_value_cansleep(gpio_data->gpio_pwm,
+ gpio_data->polarity ? 0 : 1);
+ gpio_data->pin_on = true;
+}
+
+enum hrtimer_restart gpio_pwm_timer(struct hrtimer *timer)
+{
+ struct gpio_pwm_data *gpio_data = container_of(timer,
+ struct gpio_pwm_data,
+ timer);
+
+ if (!gpio_data->pin_on) {
+ gpio_pwm_on(gpio_data);
+ hrtimer_forward_now(&gpio_data->timer,
+ ns_to_ktime(gpio_data->on_time));
+ } else {
+ gpio_pwm_off(gpio_data);
+ hrtimer_forward_now(&gpio_data->timer,
+ ns_to_ktime(gpio_data->off_time));
+ }
+
+ return HRTIMER_RESTART;
+}
+
+static int gpio_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
+ int duty_ns, int period_ns)
+{
+ struct gpio_pwm_data *gpio_data = pwm_get_chip_data(pwm);
+
+ mutex_lock(&gpio_data->lock);
+ gpio_data->on_time = duty_ns;
+ gpio_data->off_time = period_ns - duty_ns;
+ mutex_unlock(&gpio_data->lock);
+
+ return 0;
+}
+
+static int gpio_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
+ enum pwm_polarity polarity)
+{
+ struct gpio_pwm_data *gpio_data = pwm_get_chip_data(pwm);
+
+ mutex_lock(&gpio_data->lock);
+ gpio_data->polarity = (polarity != PWM_POLARITY_NORMAL) ? true : false;
+ mutex_unlock(&gpio_data->lock);
+
+ return 0;
+}
+
+static int gpio_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct gpio_pwm_data *gpio_data = pwm_get_chip_data(pwm);
+
+ mutex_lock(&gpio_data->lock);
+
+ if (gpio_data->is_running) {
+ mutex_unlock(&gpio_data->lock);
+ return -EBUSY;
+ }
+
+ gpio_data->is_running = true;
+ hrtimer_start(&gpio_data->timer, ktime_set(0, 0),
+ HRTIMER_MODE_REL);
+
+ mutex_unlock(&gpio_data->lock);
+
+ return 0;
+}
+
+static void gpio_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct gpio_pwm_data *gpio_data = pwm_get_chip_data(pwm);
+
+ mutex_lock(&gpio_data->lock);
+
+ if (!gpio_data->is_running) {
+ mutex_unlock(&gpio_data->lock);
+ return;
+ }
+
+ hrtimer_cancel(&gpio_data->timer);
+ gpio_pwm_off(gpio_data);
+ gpio_data->is_running = false;
+
+ mutex_unlock(&gpio_data->lock);
+}
+
+static int gpio_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct gpio_pwm_data *gpio_data;
+ struct gpio_desc *gpio_pwm;
+
+ gpio_data = kzalloc(sizeof(*gpio_data), GFP_KERNEL);
+ if (!gpio_data)
+ return -ENOMEM;
+
+ gpio_pwm = gpiod_get(chip->dev, "pwm", GPIOD_OUT_LOW);
+ if (IS_ERR(gpio_pwm)) {
+ dev_err(chip->dev, "failed to retrieve pwm from dts\n");
+ return PTR_ERR(gpio_pwm);
+ }
+
+ hrtimer_init(&gpio_data->timer,
+ CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+
+ if (!hrtimer_is_hres_active(&gpio_data->timer))
+ dev_warn(chip->dev, "HR timer unavailable, restricting to, low resolution\n");
+
+ gpio_data->timer.function = &gpio_pwm_timer;
+ gpio_data->gpio_pwm = gpio_pwm;
+ gpio_data->pin_on = false;
+ gpio_data->is_running = false;
+
+ return pwm_set_chip_data(pwm, gpio_data);
+}
+
+static void gpio_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+ struct gpio_pwm_data *gpio_data = pwm_get_chip_data(pwm);
+
+ gpio_pwm_disable(chip, pwm);
+ gpiod_put(gpio_data->gpio_pwm);
+ kfree(gpio_data);
+}
+
+static const struct pwm_ops gpio_pwm_ops = {
+ .config = gpio_pwm_config,
+ .set_polarity = gpio_pwm_set_polarity,
+ .enable = gpio_pwm_enable,
+ .disable = gpio_pwm_disable,
+ .request = gpio_pwm_request,
+ .free = gpio_pwm_free,
+ .owner = THIS_MODULE,
+};
+
+static int gpio_pwm_probe(struct platform_device *pdev)
+{
+ struct gpio_pwm_chip *gpio_chip;
+ int ret;
+
+ gpio_chip = devm_kzalloc(&pdev->dev, sizeof(*gpio_chip), GFP_KERNEL);
+ if (!gpio_chip)
+ return -ENOMEM;
+
+ gpio_chip->chip.dev = &pdev->dev;
+ gpio_chip->chip.ops = &gpio_pwm_ops;
+ gpio_chip->chip.base = -1;
+ gpio_chip->chip.npwm = 1;
+
+ ret = pwmchip_add(&gpio_chip->chip);
+ if (ret < 0) {
+ dev_err(&pdev->dev, "failed to add pwm gpio chip %d\n", ret);
+ return -ENODEV;
+ }
+
+ platform_set_drvdata(pdev, gpio_chip);
+
+ return 0;
+}
+
+static int gpio_pwm_remove(struct platform_device *pdev)
+{
+ struct gpio_pwm_chip *gpio_chip = platform_get_drvdata(pdev);
+
+ return pwmchip_remove(&gpio_chip->chip);
+}
+
+static const struct of_device_id gpio_pwm_of_match[] = {
+ { .compatible = "pwm-gpio", },
+ {},
+};
+MODULE_DEVICE_TABLE(of, gpio_pwm_of_match);
+
+static struct platform_driver gpio_pwm_driver = {
+ .probe = gpio_pwm_probe,
+ .remove = gpio_pwm_remove,
+ .driver = {
+ .name = "pwm-gpio",
+ .of_match_table = of_match_ptr(gpio_pwm_of_match),
+ },
+};
+module_platform_driver(gpio_pwm_driver);
+
+MODULE_AUTHOR("Angelo Compagnucci <angelo.compagnucci@gmail.com>");
+MODULE_DESCRIPTION("Generic GPIO bit-banged PWM driver");
+MODULE_LICENSE("GPL");
This patch adds a driver to generate a PWM signal on a generic GPIO pin. Driver can use hrtimers when available to allow nano-second resolution, the precision of the resulting signal depends on the switching speed of the gpio pins, timers and the system load. Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com> --- .../devicetree/bindings/pwm/pwm-gpio.txt | 14 + drivers/pwm/Kconfig | 10 + drivers/pwm/Makefile | 1 + drivers/pwm/pwm-gpio.c | 244 ++++++++++++++++++ 4 files changed, 269 insertions(+) create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.txt create mode 100644 drivers/pwm/pwm-gpio.c