Re: [PATCH v1 1/1] power: Add simple gpio-restart driver

[Guenter Roeck <linux@roeck-us.net>]

On 08/26/2014 04:45 PM, David Riley wrote:
> This driver registers a restart handler to set a GPIO line high/low
> to reset a board based on devicetree bindings.
>
> Signed-off-by: David Riley <davidriley@chromium.org>
> ---
>   .../devicetree/bindings/gpio/gpio-restart.txt      |  48 +++++++
>   drivers/power/reset/Kconfig                        |   8 ++
>   drivers/power/reset/Makefile                       |   1 +
>   drivers/power/reset/gpio-restart.c                 | 142 +++++++++++++++++++++
>   4 files changed, 199 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/gpio/gpio-restart.txt
>   create mode 100644 drivers/power/reset/gpio-restart.c
>
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-restart.txt b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
> new file mode 100644
> index 0000000..7cd58788
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
> @@ -0,0 +1,48 @@
> +Driver a GPIO line that can be used to restart the system as a
> +restart handler.
> +
> +The driver supports both level triggered and edge triggered power off.
> +At driver load time, the driver will request the given gpio line and
> +install a restart handler. If the optional properties 'input' is
> +not found, the GPIO line will be driven in the inactive state.
> +Otherwise its configured as an input.
> +
> +When do_kernel_restart is called the various restart handlers will be tried
> +in order.  The gpio is configured as an output, and drive active, so
> +triggering a level triggered power off condition. This will also cause an
> +inactive->active edge condition, so triggering positive edge triggered
> +power off. After a delay of 100ms, the GPIO is set to inactive, thus
> +causing an active->inactive edge, triggering negative edge triggered power
> +off. After another 100ms delay the GPIO is driver active again. If the
> +power is still on and the CPU still running after a 3000ms delay, a
> +WARN_ON(1) is emitted.
> +
> +Required properties:
> +- compatible : should be "gpio-restart".
> +- gpios : The GPIO to set high/low, see "gpios property" in
> +  Documentation/devicetree/bindings/gpio/gpio.txt. If the pin should be
> +  low to power down the board set it to "Active Low", otherwise set
> +  gpio to "Active High".
> +
> +Optional properties:
> +- input : Initially configure the GPIO line as an input. Only reconfigure
> +  it to an output when the machine_restart function is called. If this optional
> +  property is not specified, the GPIO is initialized as an output in its
> +  inactive state.

Maybe describe this as open source ?

> +- priority : A priority ranging from 0 to 255 (default 128) according to
> +  the following guidelines:
> +	0:	Restart handler of last resort, with limited restart
> +		capabilities
> +	128:	Default restart handler; use if no other restart handler is
> +		expected to be available, and/or if restart functionality is
> +		sufficient to restart the entire system
> +	255:	Highest priority restart handler, will preempt all other
> +		restart handlers
> +
> +Examples:
> +
> +gpio-restart {
> +	compatible = "gpio-restart";
> +	gpios = <&gpio 4 0>;
> +	priority = /bits/ 8 <200>;
> +};
> diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
> index ca41523..f07e26c 100644
> --- a/drivers/power/reset/Kconfig
> +++ b/drivers/power/reset/Kconfig
> @@ -39,6 +39,14 @@ config POWER_RESET_GPIO
>   	  If your board needs a GPIO high/low to power down, say Y and
>   	  create a binding in your devicetree.
>
> +config POWER_RESET_GPIO_RESTART
> +	bool "GPIO restart driver"
> +	depends on OF_GPIO && POWER_RESET
> +	help
> +	  This driver supports restarting your board via a GPIO line.
> +	  If your board needs a GPIO high/low to restart, say Y and
> +	  create a binding in your devicetree.
> +
>   config POWER_RESET_HISI
>   	bool "Hisilicon power-off driver"
>   	depends on POWER_RESET && ARCH_HISI
> diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
> index a42e70e..199cb6e 100644
> --- a/drivers/power/reset/Makefile
> +++ b/drivers/power/reset/Makefile
> @@ -2,6 +2,7 @@ obj-$(CONFIG_POWER_RESET_AS3722) += as3722-poweroff.o
>   obj-$(CONFIG_POWER_RESET_AXXIA) += axxia-reset.o
>   obj-$(CONFIG_POWER_RESET_BRCMSTB) += brcmstb-reboot.o
>   obj-$(CONFIG_POWER_RESET_GPIO) += gpio-poweroff.o
> +obj-$(CONFIG_POWER_RESET_GPIO_RESTART) += gpio-restart.o
>   obj-$(CONFIG_POWER_RESET_HISI) += hisi-reboot.o
>   obj-$(CONFIG_POWER_RESET_MSM) += msm-poweroff.o
>   obj-$(CONFIG_POWER_RESET_QNAP) += qnap-poweroff.o
> diff --git a/drivers/power/reset/gpio-restart.c b/drivers/power/reset/gpio-restart.c
> new file mode 100644
> index 0000000..2cbff64
> --- /dev/null
> +++ b/drivers/power/reset/gpio-restart.c
> @@ -0,0 +1,142 @@
> +/*
> + * Toggles a GPIO pin to restart a device
> + *
> + * Copyright (C) 2014 Google, Inc.
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * 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.
> + *
> + * Based on the gpio-poweroff driver.
> + */
> +#include <linux/reboot.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/delay.h>
> +#include <linux/platform_device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/of_platform.h>
> +#include <linux/module.h>
> +
> +struct gpio_restart {
> +	struct gpio_desc *reset_gpio;
> +	struct notifier_block restart_handler;
> +};
> +
> +static int gpio_restart_notify(struct notifier_block *this,
> +				unsigned long mode, void *cmd)
> +{
> +	struct gpio_restart *gpio_restart =
> +		container_of(this, struct gpio_restart, restart_handler);
> +
> +	BUG_ON(!gpio_restart->reset_gpio);
> +
Is this really necessary ? First, it can't really happen,
but if it happens anyway I am not sure if there might be
a possibility for recursiveness. After all, this is called
from machine_restart().

> +	/* drive it active, also inactive->active edge */
> +	gpiod_direction_output(gpio_restart->reset_gpio, 1);
> +	mdelay(100);
> +
> +	/* drive inactive, also active->inactive edge */
> +	gpiod_set_value(gpio_restart->reset_gpio, 0);
> +	mdelay(100);
> +
> +	/* drive it active, also inactive->active edge */
> +	gpiod_set_value(gpio_restart->reset_gpio, 1);
> +
> +	/* give it some time */
> +	mdelay(3000);
> +
Should those delays be parameters ?

> +	WARN_ON(1);
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static int gpio_restart_probe(struct platform_device *pdev)
> +{
> +	struct gpio_restart *gpio_restart;
> +	bool input = false;
> +	u8 priority;
> +	int ret;
> +
> +	gpio_restart = devm_kzalloc(&pdev->dev, sizeof(*gpio_restart),
> +			GFP_KERNEL);
> +	if (!gpio_restart)
> +		return -ENOMEM;
> +
> +	gpio_restart->reset_gpio = devm_gpiod_get(&pdev->dev, NULL);
> +	if (IS_ERR(gpio_restart->reset_gpio))
> +		return PTR_ERR(gpio_restart->reset_gpio);
> +
There is now a flags parameter to devm_gpiod_get which should help
handling input/output with a single call.

> +	gpio_restart->restart_handler.notifier_call = gpio_restart_notify;
> +	gpio_restart->restart_handler.priority = 128;
> +
> +	platform_set_drvdata(pdev, gpio_restart);
> +
> +	input = of_property_read_bool(pdev->dev.of_node, "input");
> +	if (input) {
> +		if (gpiod_direction_input(gpio_restart->reset_gpio)) {
> +			dev_err(&pdev->dev,
> +				"Could not set direction of reset GPIO to input\n");
> +			return -ENODEV;
> +		}
> +	} else {
> +		if (gpiod_direction_output(gpio_restart->reset_gpio, 0)) {
> +			dev_err(&pdev->dev,
> +				"Could not set direction of reset GPIO\n");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	if (!of_property_read_u8(pdev->dev.of_node, "priority", &priority))
> +		gpio_restart->restart_handler.priority = priority;
> +
> +	ret = register_restart_handler(&gpio_restart->restart_handler);
> +	if (ret) {
> +		dev_err(&pdev->dev, "%s: cannot register restart handler, %d\n",
> +				__func__, ret);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static int gpio_restart_remove(struct platform_device *pdev)
> +{
> +	struct gpio_restart *gpio_restart = platform_get_drvdata(pdev);
> +	int ret;
> +
> +	ret = unregister_restart_handler(&gpio_restart->restart_handler);
> +	if (ret) {
> +		dev_err(&pdev->dev,
> +				"%s: cannot unregister restart handler, %d\n",
> +				__func__, ret);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id of_gpio_restart_match[] = {
> +	{ .compatible = "gpio-restart", },
> +	{},
> +};
> +
> +static struct platform_driver gpio_restart_driver = {
> +	.probe = gpio_restart_probe,
> +	.remove = gpio_restart_remove,
> +	.driver = {
> +		.name = "restart-gpio",
> +		.owner = THIS_MODULE,
> +		.of_match_table = of_gpio_restart_match,
> +	},
> +};
> +
> +module_platform_driver(gpio_restart_driver);
> +
> +MODULE_AUTHOR("David Riley <davidriley@chromium.org>");
> +MODULE_DESCRIPTION("GPIO restart driver");
> +MODULE_LICENSE("GPL");
>