pwm: gpio: Add a generic gpio based PWM driver

From: Olliver Schinagl <oliver@schinagl.nl>

This patch adds a bit-banging gpio PWM driver. It makes use of hrtimers,
to allow nano-second resolution, though it obviously strongly depends on
the switching speed of the gpio pins, hrtimer and system load.

Each pwm node can have 1 or more "pwm-gpio" entries, which will be
treated as pwm's as part of a pwm chip.

Change-Id: Idd42bf6d79f8ce52275a15965b02af470f28da7c
Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>

Documentation/devicetree/bindings/pwm/pwm-gpio.txt

@@ -0,0 +1,18 @@
+Generic GPIO bit-banged PWM driver
+
+Required properties:
+  - compatible: should be "pwm-gpio"
+  - #pwm-cells: should be 3, see pwm.txt in this directory for a general
+    description of the cells format.
+  - pwm-gpios: one or more gpios 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-cells = 3;
+		pwm-gpios = <&pio 7 1 GPIO_ACTIVE_LOW>;
+		pwm-gpios = <&pio 7 2 GPIO_ACTIVE_LOW>;
+	};

MAINTAINERS

@@ -5252,6 +5252,11 @@ F:	drivers/i2c/muxes/i2c-mux-gpio.c
 F:	include/linux/i2c-mux-gpio.h
 F:	Documentation/i2c/muxes/i2c-mux-gpio
 
+GENERIC GPIO PWM DRIVER
+M:	Olliver Schinagl <oliver@schinagl.nl>
+S:	Maintained
+F:	drivers/pwm/pwm-gpio.c
+
 GENERIC HDLC (WAN) DRIVERS
 M:	Krzysztof Halasa <khc@pm.waw.pl>
 W:	http://www.kernel.org/pub/linux/utils/net/hdlc/

drivers/pwm/Kconfig

@@ -188,6 +188,21 @@ config PWM_IMG
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-img
 
+config PWM_GPIO
+	tristate "Generic GPIO bit-banged PWM driver"
+	depends on OF
+	depends on GPIOLIB
+	help
+	  Some platforms do not offer any hardware PWM capabilities but do have
+	  General Purpose Input Output (GPIO) pins available. Using the kernels
+	  High-Resolution Timer API this driver tries to toggle GPIO using the
+	  generic kernel PWM framework. The maximum frequency and/or accuracy
+	  is dependent on several factors such as system load and the maximum
+	  speed a pin can be toggled at the hardware.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-gpio.
+
 config PWM_IMX
 	tristate "i.MX PWM support"
 	depends on ARCH_MXC

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_IMG)		+= pwm-img.o
 obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o
 obj-$(CONFIG_PWM_JZ4740)	+= pwm-jz4740.o

drivers/pwm/pwm-gpio.c

@@ -0,0 +1,254 @@
+/*
+ * Copyright (c) 2015 Olliver Schinagl <oliver@schinagl.nl>
+ *
+ * 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.
+ *
+ * This driver adds a high-resolution timer based PWM driver. Since this is a
+ * bit-banged driver, accuracy will always depend on a lot of factors, such as
+ * GPIO toggle speed and system load.
+ */
+
+#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>
+
+#define DRV_NAME "pwm-gpio"
+
+struct gpio_pwm_data {
+	struct hrtimer timer;
+	struct gpio_desc *gpiod;
+	bool polarity;
+	bool pin_on;
+	int on_time;
+	int off_time;
+	bool run;
+};
+
+struct gpio_pwm_chip {
+	struct pwm_chip chip;
+};
+
+static void gpio_pwm_off(struct gpio_pwm_data *gpio_data)
+{
+	gpiod_set_value_cansleep(gpio_data->gpiod, gpio_data->polarity ? 0 : 1);
+}
+
+static void gpio_pwm_on(struct gpio_pwm_data *gpio_data)
+{
+	gpiod_set_value_cansleep(gpio_data->gpiod, gpio_data->polarity ? 1 : 0);
+}
+
+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->run) {
+		gpio_pwm_off(gpio_data);
+		gpio_data->pin_on = false;
+		return HRTIMER_NORESTART;
+	}
+
+	if (!gpio_data->pin_on) {
+		hrtimer_forward_now(&gpio_data->timer,
+				    ns_to_ktime(gpio_data->on_time));
+		gpio_pwm_on(gpio_data);
+		gpio_data->pin_on = true;
+	} else {
+		hrtimer_forward_now(&gpio_data->timer,
+				    ns_to_ktime(gpio_data->off_time));
+		gpio_pwm_off(gpio_data);
+		gpio_data->pin_on = false;
+	}
+
+	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);
+
+	gpio_data->on_time = duty_ns;
+	gpio_data->off_time = period_ns - duty_ns;
+
+	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);
+
+	gpio_data->polarity = (polarity != PWM_POLARITY_NORMAL) ? true : false;
+
+	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);
+
+	if (gpio_data->run)
+		return -EBUSY;
+
+	gpio_data->run = true;
+	if (gpio_data->off_time) {
+		hrtimer_start(&gpio_data->timer, ktime_set(0, 0),
+			      HRTIMER_MODE_REL);
+	} else {
+		if (gpio_data->on_time)
+			gpio_pwm_on(gpio_data);
+		else
+			gpio_pwm_off(gpio_data);
+	}
+
+	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);
+
+	gpio_data->run = false;
+	if (!gpio_data->off_time)
+		gpio_pwm_off(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,
+	.owner = THIS_MODULE,
+};
+
+static int gpio_pwm_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct gpio_pwm_chip *gpio_chip;
+	int npwm, i;
+	int hrtimer = 0;
+
+	npwm = of_gpio_named_count(pdev->dev.of_node, "pwm-gpios");
+	if (npwm < 1)
+		return -ENODEV;
+
+	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 = npwm;
+	gpio_chip->chip.of_xlate = of_pwm_xlate_with_flags;
+	gpio_chip->chip.of_pwm_n_cells = 3;
+	gpio_chip->chip.can_sleep = true;
+
+	ret = pwmchip_add(&gpio_chip->chip);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "failed to add PWM chip: %d\n", ret);
+		return ret;
+	}
+
+	for (i = 0; i < npwm; i++) {
+		struct gpio_desc *gpiod;
+		struct gpio_pwm_data *gpio_data;
+
+		gpiod = devm_gpiod_get_index(&pdev->dev, "pwm", i,
+					     GPIOD_OUT_LOW);
+		if (IS_ERR(gpiod)) {
+			int error;
+
+			error = PTR_ERR(gpiod);
+			if (error != -EPROBE_DEFER)
+				dev_err(&pdev->dev,
+					"failed to get gpio flags, error: %d\n",
+					error);
+			return error;
+		}
+
+		gpio_data = devm_kzalloc(&pdev->dev, sizeof(*gpio_data),
+					 GFP_KERNEL);
+
+		hrtimer_init(&gpio_data->timer,
+			     CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+		gpio_data->timer.function = &gpio_pwm_timer;
+		gpio_data->gpiod = gpiod;
+		gpio_data->pin_on = false;
+		gpio_data->run = false;
+
+		if (hrtimer_is_hres_active(&gpio_data->timer))
+			hrtimer++;
+
+		pwm_set_chip_data(&gpio_chip->chip.pwms[i], gpio_data);
+	}
+	if (!hrtimer) {
+		dev_warn(&pdev->dev, "unable to use High-Resolution timer,");
+		dev_warn(&pdev->dev, "%s is restricted to low resolution.",
+			 DRV_NAME);
+	}
+
+	platform_set_drvdata(pdev, gpio_chip);
+
+	dev_info(&pdev->dev, "%d gpio pwms loaded\n", npwm);
+
+	return 0;
+}
+
+static int gpio_pwm_remove(struct platform_device *pdev)
+{
+	struct gpio_pwm_chip *gpio_chip;
+	int i;
+
+	gpio_chip = platform_get_drvdata(pdev);
+	for (i = 0; i < gpio_chip->chip.npwm; i++) {
+		struct gpio_pwm_data *gpio_data;
+
+		gpio_data = pwm_get_chip_data(&gpio_chip->chip.pwms[i]);
+
+		hrtimer_cancel(&gpio_data->timer);
+	}
+
+	return pwmchip_remove(&gpio_chip->chip);
+}
+
+static const struct of_device_id gpio_pwm_of_match[] = {
+	{ .compatible = DRV_NAME, },
+	{/* sentinel */},
+};
+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 = DRV_NAME,
+		.of_match_table = of_match_ptr(gpio_pwm_of_match),
+	},
+};
+module_platform_driver(gpio_pwm_driver);
+
+MODULE_AUTHOR("Olliver Schinagl <oliver@schinagl.nl>");
+MODULE_DESCRIPTION("Generic GPIO bit-banged PWM driver");
+MODULE_LICENSE("GPL");