leds: gpio: Allow LED to retain state at shutdown

In some systems, such as Baseboard Management Controllers (BMCs), we
want to retain the state of LEDs across a reboot of the BMC (whilst the
host remains up). Implement support for the retain-state-shutdown
devicetree property in leds-gpio.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Pavel Machek <pavel@ucw.cz>
Tested-by: Brandon Wyman <bjwyman@gmail.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

drivers/leds/leds-gpio.c

@@ -134,6 +134,8 @@ static int create_gpio_led(const struct gpio_led *template,
 		led_dat->cdev.flags |= LED_CORE_SUSPENDRESUME;
 	if (template->panic_indicator)
 		led_dat->cdev.flags |= LED_PANIC_INDICATOR;
+	if (template->retain_state_shutdown)
+		led_dat->cdev.flags |= LED_RETAIN_AT_SHUTDOWN;
 
 	ret = gpiod_direction_output(led_dat->gpiod, state);
 	if (ret < 0)
@@ -205,6 +207,8 @@ static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
 
 		if (fwnode_property_present(child, "retain-state-suspended"))
 			led.retain_state_suspended = 1;
+		if (fwnode_property_present(child, "retain-state-shutdown"))
+			led.retain_state_shutdown = 1;
 		if (fwnode_property_present(child, "panic-indicator"))
 			led.panic_indicator = 1;
 
@@ -267,6 +271,7 @@ static void gpio_led_shutdown(struct platform_device *pdev)
 	for (i = 0; i < priv->num_leds; i++) {
 		struct gpio_led_data *led = &priv->leds[i];
 
+		if (!(led->cdev.flags & LED_RETAIN_AT_SHUTDOWN))
 			gpio_led_set(&led->cdev, LED_OFF);
 	}
 }

include/linux/leds.h

@@ -49,6 +49,7 @@ struct led_classdev {
 #define LED_HW_PLUGGABLE	(1 << 19)
 #define LED_PANIC_INDICATOR	(1 << 20)
 #define LED_BRIGHT_HW_CHANGED	(1 << 21)
+#define LED_RETAIN_AT_SHUTDOWN	(1 << 22)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;
@@ -392,6 +393,7 @@ struct gpio_led {
 	unsigned	retain_state_suspended : 1;
 	unsigned	panic_indicator : 1;
 	unsigned	default_state : 2;
+	unsigned	retain_state_shutdown : 1;
 	/* default_state should be one of LEDS_GPIO_DEFSTATE_(ON|OFF|KEEP) */
 	struct gpio_desc *gpiod;
 };