leds: trigger: Load trigger modules on-demand if used as default trigger

Even if a trigger is set as default trigger for a LED device,
the respective trigger module (if built as module) isn't automatically
loaded by the kernel if the LED device is registered. I think we can
do better. Try to load the module asynchronously by alias
ledtrig:<trigger name>. This requires that such an alias is added to
relevant triggers.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/79adb260-06ad-443a-a68e-abe4498c3298@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index bd59a14a4a90c2394268418e9347c50e1aff4154..71cb0aee528c814d75d26d8ff23ae315eea9c70a 100644 (file)
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -250,6 +250,7 @@ EXPORT_SYMBOL_GPL(led_trigger_remove);
 void led_trigger_set_default(struct led_classdev *led_cdev)
 {
        struct led_trigger *trig;
+       bool found = false;
 
        if (!led_cdev->default_trigger)
                return;
@@ -259,6 +260,7 @@ void led_trigger_set_default(struct led_classdev *led_cdev)
        list_for_each_entry(trig, &trigger_list, next_trig) {
                if (!strcmp(led_cdev->default_trigger, trig->name) &&
                    trigger_relevant(led_cdev, trig)) {
+                       found = true;
                        led_cdev->flags |= LED_INIT_DEFAULT_TRIGGER;
                        led_trigger_set(led_cdev, trig);
                        break;
@@ -266,6 +268,13 @@ void led_trigger_set_default(struct led_classdev *led_cdev)
        }
        up_write(&led_cdev->trigger_lock);
        up_read(&triggers_list_lock);
+
+       /*
+        * If default trigger wasn't found, maybe trigger module isn't loaded yet.
+        * Once loaded it will re-probe with all led_cdev's.
+        */
+       if (!found)
+               request_module_nowait("ledtrig:%s", led_cdev->default_trigger);
 }
 EXPORT_SYMBOL_GPL(led_trigger_set_default);