pwm: pwm-gpio: Generic GPIO bit-banged PWM driver

diff --git a/Documentation/devicetree/bindings/pwm/pwm-gpio.txt b/Documentation/devicetree/bindings/pwm/pwm-gpio.txt
new file mode 100644
index 000000000000..fe15569c0332
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/pwm-gpio.txt
@@ -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>;
+	};
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 0937e1c047ac..47c8b68a5f13 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -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
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 18b89d7fd092..4d2aad6eb3bc 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -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
diff --git a/drivers/pwm/pwm-gpio.c b/drivers/pwm/pwm-gpio.c
new file mode 100644
index 000000000000..6d38a47f82fb
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -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");