[RFC PATCH 1/9] leds: Load trigger modules on-demand if used as hw control trigger

[Rong Zhang]

In the following patches, we are about to support hardware initiated
trigger transitions to/from the device's hw control trigger. In case
the LED hardware switches itself to hw control mode, hw control trigger
must be loaded before so that the transition can be processed.

Load the trigger module specified by hw_control_trigger, so that
hardware initiated trigger transitions can be processed when the hw
control trigger is compiled as a module.

Signed-off-by: Rong Zhang <i@xxxxxxxx>
---
 drivers/leds/led-class.c    |  1 +
 drivers/leds/led-triggers.c | 33 +++++++++++++++++++++++++++++++++
 drivers/leds/leds.h         |  1 +
 3 files changed, 35 insertions(+)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index d34a194535604..0fa45f22246e3 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -576,6 +576,7 @@ int led_classdev_register_ext(struct device *parent,
 
 #ifdef CONFIG_LEDS_TRIGGERS
 	led_trigger_set_default(led_cdev);
+	led_load_hw_control_trigger(led_cdev);
 #endif
 
 	mutex_unlock(&led_cdev->led_access);
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index b1223218bda11..3066bc91a5f94 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -313,6 +313,39 @@ void led_trigger_set_default(struct led_classdev *led_cdev)
 }
 EXPORT_SYMBOL_GPL(led_trigger_set_default);
 
+static inline bool led_match_hw_control_trigger(struct led_classdev *led_cdev,
+						struct led_trigger *trig)
+{
+	return (!strcmp(led_cdev->hw_control_trigger, trig->name) &&
+		trigger_relevant(led_cdev, trig));
+}
+
+void led_load_hw_control_trigger(struct led_classdev *led_cdev)
+{
+	struct led_trigger *trig;
+	bool found = false;
+
+	if (!led_cdev->hw_control_trigger)
+		return;
+
+	/* default_trigger is handled by led_trigger_set_default(). */
+	if (led_cdev->default_trigger &&
+	    !strcmp(led_cdev->default_trigger, led_cdev->hw_control_trigger))
+		return;
+
+	down_read(&triggers_list_lock);
+	list_for_each_entry(trig, &trigger_list, next_trig) {
+		found = led_match_hw_control_trigger(led_cdev, trig);
+		if (found)
+			break;
+	}
+	up_read(&triggers_list_lock);
+
+	if (!found)
+		request_module_nowait("ledtrig:%s", led_cdev->hw_control_trigger);
+}
+EXPORT_SYMBOL_GPL(led_load_hw_control_trigger);
+
 /* LED Trigger Interface */
 
 int led_trigger_register(struct led_trigger *trig)
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index bee46651e068f..e85afd4d04fd0 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -21,6 +21,7 @@ void led_init_core(struct led_classdev *led_cdev);
 void led_stop_software_blink(struct led_classdev *led_cdev);
 void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value);
 void led_set_brightness_nosleep(struct led_classdev *led_cdev, unsigned int value);
+void led_load_hw_control_trigger(struct led_classdev *led_cdev);
 ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
 			const struct bin_attribute *attr, char *buf,
 			loff_t pos, size_t count);
-- 
2.51.0