[PATCH 07/10] pwm: gpio: Add a generic gpio based PWM driver

Olliver Schinagl
2015-10-26T21:35:37Z

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.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
---
Documentation/devicetree/bindings/pwm/pwm-gpio.txt | 18 ++
MAINTAINERS | 5 +
drivers/pwm/Kconfig | 15 ++
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-gpio.c | 253 +++++++++++++++++++++
5 files changed, 292 insertions(+)
create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.txt
create mode 100644 drivers/pwm/pwm-gpio.c

diff --git a/Documentation/devicetree/bindings/pwm/pwm-gpio.txt b/Documentation/devicetree/bindings/pwm/pwm-gpio.txt
new file mode 100644
index 0000000..336f61f
--- /dev/null
+++ b/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>;
+ };
diff --git a/MAINTAINERS b/MAINTAINERS
index 7ba7ab7..0ae7fbf 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4555,6 +4555,11 @@ 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/
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 0cfaf6b..c0bc296 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -170,6 +170,21 @@ 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
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 69b8275..96aa9aa 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_PWM_CLPS711X) += pwm-clps711x.o
obj-$(CONFIG_PWM_CRC) += pwm-crc.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
diff --git a/drivers/pwm/pwm-gpio.c b/drivers/pwm/pwm-gpio.c
new file mode 100644
index 0000000..8b588fb
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -0,0 +1,253 @@
+/*
+ * 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");
--
2.6.1