[PATCH leds + devicetree v1 1/2] leds: trigger: add DT `trigger-sources` validating method

[Marek Behún <marek.behun@xxxxxx>]

Currently we use the `linux,default-trigger` device tree property of a
LED to define the default trigger which should be activated for a LED.

But the LED device tree binding also documents the `trigger-sources`
property, which specifies the source device which should be triggering
the LED.

The `trigger-sources` property is currently implemented only in
drivers/usb/core/ledtrig-usbport.c.

Lets add a method to struct led_trigger which, if implemented, can check
whether this trigger should be enabled as default. This check shall be
done by checking whether the specified `trigger-sources` refers to a
device compatible with the trigger.

Signed-off-by: Marek Behún <marek.behun@xxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: devicetree@xxxxxxxxxxxxxxx
---
 drivers/leds/led-triggers.c | 26 ++++++++++++++++++--------
 include/linux/leds.h        |  6 ++++++
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 91da90cfb11d9..c96577f0bfe97 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -243,18 +243,30 @@ void led_trigger_remove(struct led_classdev *led_cdev)
 }
 EXPORT_SYMBOL_GPL(led_trigger_remove);
 
+static bool trigger_is_default(struct led_classdev *led_cdev,
+			       struct led_trigger *trig)
+{
+	if (!trigger_relevant(led_cdev, trig))
+		return false;
+
+	if (led_cdev->default_trigger &&
+	    !strcmp(led_cdev->default_trigger, trig->name))
+		return true;
+
+	if (trig->has_valid_source && trig->has_valid_source(led_cdev))
+		return true;
+
+	return false;
+}
+
 void led_trigger_set_default(struct led_classdev *led_cdev)
 {
 	struct led_trigger *trig;
 
-	if (!led_cdev->default_trigger)
-		return;
-
 	down_read(&triggers_list_lock);
 	down_write(&led_cdev->trigger_lock);
 	list_for_each_entry(trig, &trigger_list, next_trig) {
-		if (!strcmp(led_cdev->default_trigger, trig->name) &&
-		    trigger_relevant(led_cdev, trig)) {
+		if (trigger_is_default(led_cdev, trig)) {
 			led_cdev->flags |= LED_INIT_DEFAULT_TRIGGER;
 			led_trigger_set(led_cdev, trig);
 			break;
@@ -306,9 +318,7 @@ int led_trigger_register(struct led_trigger *trig)
 	down_read(&leds_list_lock);
 	list_for_each_entry(led_cdev, &leds_list, node) {
 		down_write(&led_cdev->trigger_lock);
-		if (!led_cdev->trigger && led_cdev->default_trigger &&
-		    !strcmp(led_cdev->default_trigger, trig->name) &&
-		    trigger_relevant(led_cdev, trig)) {
+		if (!led_cdev->trigger && trigger_is_default(led_cdev, trig)) {
 			led_cdev->flags |= LED_INIT_DEFAULT_TRIGGER;
 			led_trigger_set(led_cdev, trig);
 		}
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 6a8d6409c993e..4cbb826e4bec4 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -352,6 +352,12 @@ struct led_trigger {
 	int		(*activate)(struct led_classdev *led_cdev);
 	void		(*deactivate)(struct led_classdev *led_cdev);
 
+	/*
+	 * Check whether LED has defined valid source for this trigger.
+	 * If yes, this trigger should be set as default trigger for LED.
+	 */
+	bool		(*has_valid_source)(struct led_classdev *led_cdev);
+
 	/* LED-private triggers have this set */
 	struct led_hw_trigger_type *trigger_type;
 
-- 
2.26.2