leds: Add the "input" trigger, for pwr_led

The "input" trigger makes the associated GPIO an input.  This is to support
the Raspberry Pi PWR LED, which is driven by external hardware in normal use.

N.B. pwr_led is not available on Model A or B boards.

leds-gpio: Implement the brightness_get method

The power LED uses some clever logic that means it is driven
by a voltage measuring circuit when configured as input, otherwise
it is driven by the GPIO output value. This patch wires up the
brightness_get method for leds-gpio so that user-space can monitor
the LED value via /sys/class/gpio/led1/brightness. Using the input
trigger this returns an indication of the system power health,
otherwise it is just whatever value the trigger has written most
recently.

See: https://github.com/raspberrypi/linux/issues/1064

drivers/leds/leds-gpio.c

@@ -47,8 +47,15 @@ static void gpio_led_set(struct led_classdev *led_cdev,
 		led_dat->platform_gpio_blink_set(led_dat->gpiod, level,
 						 NULL, NULL);
 		led_dat->blinking = 0;
+	} else if (led_dat->cdev.flags & SET_GPIO_INPUT) {
+		gpiod_direction_input(led_dat->gpiod);
+		led_dat->cdev.flags &= ~SET_GPIO_INPUT;
+	} else if (led_dat->cdev.flags & SET_GPIO_OUTPUT) {
+		gpiod_direction_output(led_dat->gpiod, level);
+		led_dat->cdev.flags &= ~SET_GPIO_OUTPUT;
 	} else {
-		if (led_dat->can_sleep)
+		if (led_dat->can_sleep ||
+			(led_dat->cdev.flags & (SET_GPIO_INPUT | SET_GPIO_OUTPUT) ))
 			gpiod_set_value_cansleep(led_dat->gpiod, level);
 		else
 			gpiod_set_value(led_dat->gpiod, level);
@@ -62,6 +69,13 @@ static int gpio_led_set_blocking(struct led_classdev *led_cdev,
 	return 0;
 }
 
+static enum led_brightness gpio_led_get(struct led_classdev *led_cdev)
+{
+	struct gpio_led_data *led_dat =
+		container_of(led_cdev, struct gpio_led_data, cdev);
+	return gpiod_get_value_cansleep(led_dat->gpiod) ? LED_FULL : LED_OFF;
+}
+
 static int gpio_blink_set(struct led_classdev *led_cdev,
 	unsigned long *delay_on, unsigned long *delay_off)
 {
@@ -90,6 +104,7 @@ static int create_gpio_led(const struct gpio_led *template,
 		led_dat->platform_gpio_blink_set = blink_set;
 		led_dat->cdev.blink_set = gpio_blink_set;
 	}
+	led_dat->cdev.brightness_get = gpio_led_get;
 	if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP) {
 		state = gpiod_get_value_cansleep(led_dat->gpiod);
 		if (state < 0)

drivers/leds/trigger/Kconfig

@@ -115,6 +115,13 @@ config LEDS_TRIGGER_CAMERA
 	  This enables direct flash/torch on/off by the driver, kernel space.
 	  If unsure, say Y.
 
+config LEDS_TRIGGER_INPUT
+	tristate "LED Input Trigger"
+	depends on LEDS_TRIGGERS
+	help
+	  This allows the GPIOs assigned to be LEDs to be initialised to inputs.
+	  If unsure, say Y.
+
 config LEDS_TRIGGER_PANIC
 	bool "LED Panic Trigger"
 	help

drivers/leds/trigger/Makefile

@@ -11,6 +11,7 @@ obj-$(CONFIG_LEDS_TRIGGER_ACTIVITY)	+= ledtrig-activity.o
 obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON)	+= ledtrig-default-on.o
 obj-$(CONFIG_LEDS_TRIGGER_TRANSIENT)	+= ledtrig-transient.o
 obj-$(CONFIG_LEDS_TRIGGER_CAMERA)	+= ledtrig-camera.o
+obj-$(CONFIG_LEDS_TRIGGER_INPUT)	+= ledtrig-input.o
 obj-$(CONFIG_LEDS_TRIGGER_PANIC)	+= ledtrig-panic.o
 obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
 obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o

drivers/leds/trigger/ledtrig-input.c

@@ -0,0 +1,55 @@
+/*
+ * Set LED GPIO to Input "Trigger"
+ *
+ * Copyright 2015 Phil Elwell <phil@raspberrypi.org>
+ *
+ * Based on Nick Forbes's ledtrig-default-on.c.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/leds.h>
+#include <linux/gpio.h>
+#include "../leds.h"
+
+static int input_trig_activate(struct led_classdev *led_cdev)
+{
+	led_cdev->flags |= SET_GPIO_INPUT;
+	led_set_brightness(led_cdev, 0);
+	return 0;
+}
+
+static void input_trig_deactivate(struct led_classdev *led_cdev)
+{
+	led_cdev->flags |= SET_GPIO_OUTPUT;
+	led_set_brightness(led_cdev, 0);
+}
+
+static struct led_trigger input_led_trigger = {
+	.name     = "input",
+	.activate = input_trig_activate,
+	.deactivate = input_trig_deactivate,
+};
+
+static int __init input_trig_init(void)
+{
+	return led_trigger_register(&input_led_trigger);
+}
+
+static void __exit input_trig_exit(void)
+{
+	led_trigger_unregister(&input_led_trigger);
+}
+
+module_init(input_trig_init);
+module_exit(input_trig_exit);
+
+MODULE_AUTHOR("Phil Elwell <phil@raspberrypi.org>");
+MODULE_DESCRIPTION("Set LED GPIO to Input \"trigger\"");
+MODULE_LICENSE("GPL");

include/linux/leds.h

@@ -85,6 +85,9 @@ struct led_classdev {
 #define LED_BRIGHT_HW_CHANGED	BIT(21)
 #define LED_RETAIN_AT_SHUTDOWN	BIT(22)
 #define LED_INIT_DEFAULT_TRIGGER BIT(23)
+	/* Additions for Raspberry Pi PWR LED */
+#define SET_GPIO_INPUT		BIT(30)
+#define SET_GPIO_OUTPUT		BIT(31)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;