BCM270x_DT: Add pwr_led, and the required "input" trigger

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: #1064

drivers/leds/leds-gpio.c

@@ -42,6 +42,13 @@ static void gpio_led_work(struct work_struct *work)
  led_dat->platform_gpio_blink_set(led_dat->gpiod,
  led_dat->new_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, led_dat->new_level);
+ led_dat->cdev.flags &= ~SET_GPIO_OUTPUT;
  } else
  gpiod_set_value_cansleep(led_dat->gpiod, led_dat->new_level);
 }
@@ -62,7 +69,8 @@ static void gpio_led_set(struct led_classdev *led_cdev,
  * seem to have a reliable way to know if we're already in one; so
  * let's just assume the worst.
  */
- if (led_dat->can_sleep) {
+ if (led_dat->can_sleep ||
+ (led_dat->cdev.flags & (SET_GPIO_INPUT | SET_GPIO_OUTPUT) )) {
  led_dat->new_level = level;
  schedule_work(&led_dat->work);
  } else {
@@ -75,6 +83,13 @@ static void gpio_led_set(struct led_classdev *led_cdev,
  }
 }
 
+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)
 {
@@ -131,6 +146,7 @@ static int create_gpio_led(const struct gpio_led *template,
  led_dat->cdev.blink_set = gpio_blink_set;
  }
  led_dat->cdev.brightness_set = gpio_led_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);
  else

drivers/leds/trigger/Kconfig

@@ -108,4 +108,11 @@ 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.
+
 endif # LEDS_TRIGGERS

drivers/leds/trigger/Makefile

@@ -8,3 +8,4 @@ obj-$(CONFIG_LEDS_TRIGGER_CPU) += ledtrig-cpu.o
 obj-$(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

drivers/leds/trigger/ledtrig-input.c

@@ -0,0 +1,54 @@
+/*
+ * 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 void input_trig_activate(struct led_classdev *led_cdev)
+{
+ led_cdev->flags |= SET_GPIO_INPUT;
+ led_set_brightness_async(led_cdev, 0);
+}
+
+static void input_trig_deactivate(struct led_classdev *led_cdev)
+{
+ led_cdev->flags |= SET_GPIO_OUTPUT;
+ led_set_brightness_async(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

@@ -48,6 +48,9 @@ struct led_classdev {
 #define SET_BRIGHTNESS_ASYNC (1 << 21)
 #define SET_BRIGHTNESS_SYNC (1 << 22)
 #define LED_DEV_CAP_FLASH (1 << 23)
+ /* Additions for Raspberry Pi PWR LED */
+#define SET_GPIO_INPUT (1 << 30)
+#define SET_GPIO_OUTPUT (1 << 31)
 
  /* Set LED brightness level */
  /* Must not sleep, use a workqueue if needed */