Re: [PATCH 3/3] Input: add generic gpio brownout driver

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Marco,

On Tue, Sep 25, 2018 at 11:42:30AM +0200, Marco Felsch wrote:
> A brownout can be detected in several ways e.g. a deticated pin on the
> soc, a external pmic or by another external hardware which informs the
> host via a gpio line.
> 
> This patch adds the support for a generic gpio-based brownout
> detection. Upon a brownout the host system gets informed and the driver
> sends a keycode signal to the userspace. Per default this signal is
> mapped to KEY_POWER, so the system will shoutdown.

I do not believe this functionality should be exposed as an input
device, as it has nothing to do with human interaction with the
computing device. To me this is akin over-current on a USB port, or
carrier signal on network interfaces.

Why don't you simply send uevent for this platform device when you
detect brownout, and have whatever entity is responsible for power
management policy on your system listen to such events?

Thanks.

> 
> Additional the driver supports releasing registered devices from their
> drivers, see Documentation/devicetree/bindings/input/gpio-brownout.txt
> for more details.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  .../bindings/input/gpio-brownout.txt          |  36 ++++
>  drivers/input/misc/Kconfig                    |  12 ++
>  drivers/input/misc/Makefile                   |   1 +
>  drivers/input/misc/gpio-brownout.c            | 166 ++++++++++++++++++
>  4 files changed, 215 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/input/gpio-brownout.txt
>  create mode 100644 drivers/input/misc/gpio-brownout.c
> 
> diff --git a/Documentation/devicetree/bindings/input/gpio-brownout.txt b/Documentation/devicetree/bindings/input/gpio-brownout.txt
> new file mode 100644
> index 000000000000..55fbe2aa52a9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/input/gpio-brownout.txt
> @@ -0,0 +1,36 @@
> +Device-Tree bindings for input/gpio_brownout.c driver
> +
> +Required properties:
> +- compatible: Must be "gpio-brownout"
> +- interrupt-parent: The phandle to the interrupt controller. For more details
> +  see ../interrupt-controller/interrupts.txt.
> +- interrupts: The interrupt line for a brownout detection. For more details
> +  see ../interrupt-controller/interrupts.txt.
> +
> +Optional properties:
> +- linux,code: Keycode to emit upon a brownout detection, default: KEY_POWER.
> +- release-devices: A list of i2c or spi device phandles. All listed devices
> +  will be released from their drivers in the order they listed upon a brownout
> +  detection. This can be helpful to avoid a interrupt flood, because some
> +  system designs power off all external devices immediately and keep the host
> +  on for a certain time.
> +
> +Example:
> +
> +i2c3 {
> +	temp_core: lm75@48 { };
> +	temp_chassis: lm75@49 { };
> +};
> +
> +spi1 {
> +	ts: ad7879@1 { };
> +};
> +
> +/ {
> +	gpio_brownout_det {
> +		compatible = "gpio-brownout";
> +		interrupts-parent = <&gpio3>;
> +		interrupts = <3 IRQ_TYPE_EDGE_LOW>:
> +		release-devices = <&temp_core &ts>;
> +	};
> +};
> diff --git a/drivers/input/misc/Kconfig b/drivers/input/misc/Kconfig
> index ca59a2be9bc5..6b49e681cca7 100644
> --- a/drivers/input/misc/Kconfig
> +++ b/drivers/input/misc/Kconfig
> @@ -268,6 +268,18 @@ config INPUT_GPIO_BEEPER
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called gpio-beeper.
>  
> +config INPUT_GPIO_BROWNOUT
> +	tristate "Generic GPIO Brownout detection support"
> +	depends on GPIOLIB || COMPILE_TEST
> +	help
> +	  Say Y here if you have a brownout signal connected to a GPIO pin
> +	  and want to report a keycode signal on a brownout detection.
> +
> +	  If unsure, say N.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called gpio-brownout.
> +
>  config INPUT_GPIO_DECODER
>  	tristate "Polled GPIO Decoder Input driver"
>  	depends on GPIOLIB || COMPILE_TEST
> diff --git a/drivers/input/misc/Makefile b/drivers/input/misc/Makefile
> index 9d0f9d1ff68f..8b872b5fc84a 100644
> --- a/drivers/input/misc/Makefile
> +++ b/drivers/input/misc/Makefile
> @@ -35,6 +35,7 @@ obj-$(CONFIG_INPUT_DRV2665_HAPTICS)	+= drv2665.o
>  obj-$(CONFIG_INPUT_DRV2667_HAPTICS)	+= drv2667.o
>  obj-$(CONFIG_INPUT_GP2A)		+= gp2ap002a00f.o
>  obj-$(CONFIG_INPUT_GPIO_BEEPER)		+= gpio-beeper.o
> +obj-$(CONFIG_INPUT_GPIO_BROWNOUT)	+= gpio-brownout.o
>  obj-$(CONFIG_INPUT_GPIO_DECODER)	+= gpio_decoder.o
>  obj-$(CONFIG_INPUT_HISI_POWERKEY)	+= hisi_powerkey.o
>  obj-$(CONFIG_HP_SDC_RTC)		+= hp_sdc_rtc.o
> diff --git a/drivers/input/misc/gpio-brownout.c b/drivers/input/misc/gpio-brownout.c
> new file mode 100644
> index 000000000000..23992b9e2814
> --- /dev/null
> +++ b/drivers/input/misc/gpio-brownout.c
> @@ -0,0 +1,166 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * gpio-brownout.c - Generic power fail driver
> + *
> + * Copyright (C) 2018 Pengutronix, Marco Felsch <kernel@pengutronix.de>
> + */
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/input.h>
> +#include <linux/interrupt.h>
> +#include <linux/irqreturn.h>
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/spi/spi.h>
> +
> +#define GPIO_BROWNOUT_MOD_NAME "gpio-brownout"
> +
> +struct gpio_brownout_device {
> +	struct list_head  list;
> +	struct device *dev;
> +};
> +
> +struct gpio_brownout {
> +	struct device *dev;
> +	struct input_dev *idev;
> +	unsigned short kcode;
> +	struct list_head devices;
> +};
> +
> +static irqreturn_t gpio_brownout_isr(int irq, void *dev_id)
> +{
> +	struct gpio_brownout *gb = dev_id;
> +	struct input_dev *idev = gb->idev;
> +	struct gpio_brownout_device *bout_dev, *tmp;
> +
> +	/* first inform userspace */
> +	input_report_key(idev, gb->kcode, 1);
> +	input_sync(idev);
> +
> +	/* now unregister registered drivers */
> +	list_for_each_entry_safe(bout_dev, tmp, &gb->devices, list) {
> +		device_release_driver(bout_dev->dev);
> +		list_del(&bout_dev->list);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
> +#ifdef CONFIG_OF
> +static int gpio_brownout_probe_dt(struct gpio_brownout *gb)
> +{
> +	struct device_node *np = gb->dev->of_node;
> +	struct of_phandle_iterator it;
> +	unsigned int kcode;
> +	int ret;
> +
> +	/* all dt-properties are optional */
> +	of_property_read_u32(np, "linux,code", &kcode);
> +	gb->kcode = kcode;
> +
> +	/*
> +	 * Register all devices which should be unbinded upon a brownout
> +	 * detection. At the moment only i2c and spi devices are supported
> +	 */
> +	of_for_each_phandle(&it, ret, np, "release-devices", NULL, 0) {
> +		struct gpio_brownout_device *elem;
> +		struct i2c_client *i2c_c;
> +		struct spi_device *spi_c;
> +
> +		i2c_c = of_find_i2c_device_by_node(it.node);
> +		spi_c = of_find_spi_device_by_node(it.node);
> +
> +		if (!i2c_c && !spi_c)
> +			return -EPROBE_DEFER;
> +		else if (i2c_c && spi_c)
> +			return -EINVAL;
> +
> +		elem = devm_kzalloc(gb->dev, sizeof(*elem), GFP_KERNEL);
> +		if (!elem)
> +			return -ENOMEM;
> +
> +		elem->dev = i2c_c ? &i2c_c->dev : &spi_c->dev;
> +
> +		INIT_LIST_HEAD(&elem->list);
> +		list_add_tail(&elem->list, &gb->devices);
> +	}
> +
> +	return 0;
> +}
> +#endif
> +
> +static int gpio_brownout_probe(struct platform_device *pdev)
> +{
> +	struct gpio_brownout *gb;
> +	struct input_dev *idev;
> +	int ret, irq;
> +
> +	gb = devm_kzalloc(&pdev->dev, sizeof(*gb), GFP_KERNEL);
> +	if (!gb)
> +		return -ENOMEM;
> +
> +	idev = devm_input_allocate_device(&pdev->dev);
> +	if (!idev)
> +		return -ENOMEM;
> +
> +	gb->dev = &pdev->dev;
> +	gb->idev = idev;
> +	INIT_LIST_HEAD(&gb->devices);
> +
> +	if (IS_ENABLED(CONFIG_OF)) {
> +		ret = gpio_brownout_probe_dt(gb);
> +		if (ret) {
> +			dev_err(&pdev->dev, "probe_dt failed: %d\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	idev->name = pdev->name;
> +	gb->kcode = gb->kcode == KEY_RESERVED ? KEY_POWER : gb->kcode;
> +
> +	input_set_capability(idev, EV_KEY, gb->kcode);
> +
> +	irq = platform_get_irq(pdev, 0);
> +	ret = devm_request_threaded_irq(&pdev->dev, irq, NULL,
> +					gpio_brownout_isr, IRQF_ONESHOT,
> +					GPIO_BROWNOUT_MOD_NAME, gb);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "IRQ request failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = input_register_device(idev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Input register failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id gpio_brownout_of_match[] = {
> +	{ .compatible = GPIO_BROWNOUT_MOD_NAME, },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, arm_gpio_brownout_of_match);
> +#endif
> +
> +static struct platform_driver gpio_brownout_driver = {
> +	.driver = {
> +		.name = GPIO_BROWNOUT_MOD_NAME,
> +		.of_match_table = of_match_ptr(gpio_brownout_of_match)
> +	},
> +	.probe = gpio_brownout_probe,
> +};
> +
> +module_platform_driver(gpio_brownout_driver);
> +
> +MODULE_AUTHOR("Marco Felsch <kernel@pengutronix.de>");
> +MODULE_DESCRIPTION("GPIO Brownout Detection");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.19.0
> 

-- 
Dmitry