[PATCH v2 1/2] leds: triggers: Add led_trigger_walk_leds()

[Nikolay Plastinin via B4 Relay <devnull+plaztininikolai.gmail.com@kernel.org>]

From: Nikolay Plastinin <plaztininikolai@gmail.com>

led_trigger_event() sets one brightness for all LEDs using a trigger.
A trigger which restores a different brightness per LED, such as the
input-events trigger turning keyboard backlights back on at the level
the user picked, needs to walk the trigger's LEDs itself. That means
using trig->led_cdevs and led_cdev->trig_list outside the LED core.

Add led_trigger_walk_leds(), which calls a function for each LED
using the trigger under rcu_read_lock(), the same way led_trigger_event()
does, so that such triggers do not have to walk the list themselves.

Assisted-by: LLM
Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>
---
 drivers/leds/led-triggers.c | 25 +++++++++++++++++++++++++
 include/linux/leds.h        |  7 +++++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index b1223218b..b5fc14e47 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -422,6 +422,31 @@ void led_trigger_event(struct led_trigger *trig,
 }
 EXPORT_SYMBOL_GPL(led_trigger_event);
 
+/**
+ * led_trigger_walk_leds - call a function for each LED using a trigger
+ * @trig: the trigger, may be NULL
+ * @fn: the function to call for each LED
+ * @data: pointer passed to @fn
+ *
+ * Walks the LEDs currently using @trig under rcu_read_lock() and calls @fn
+ * for each of them. This is for triggers which set a different brightness
+ * per LED, where led_trigger_event() is not enough. @fn must not sleep.
+ */
+void led_trigger_walk_leds(struct led_trigger *trig, led_trigger_walk_fn_t fn,
+			   void *data)
+{
+	struct led_classdev *led_cdev;
+
+	if (!trig)
+		return;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list)
+		fn(led_cdev, data);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(led_trigger_walk_leds);
+
 void led_mc_trigger_event(struct led_trigger *trig,
 			  unsigned int *intensity_value, unsigned int num_colors,
 			  enum led_brightness brightness)
diff --git a/include/linux/leds.h b/include/linux/leds.h
index a515f075c..c971a6aa5 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -476,6 +476,9 @@ static inline bool led_sysfs_is_disabled(struct led_classdev *led_cdev)
 #define DEFINE_LED_TRIGGER(x)		static struct led_trigger *x;
 #define DEFINE_LED_TRIGGER_GLOBAL(x)	struct led_trigger *x;
 
+/* Callback for led_trigger_walk_leds() */
+typedef void (*led_trigger_walk_fn_t)(struct led_classdev *led_cdev, void *data);
+
 #ifdef CONFIG_LEDS_TRIGGERS
 
 #define TRIG_NAME_MAX 50
@@ -521,6 +524,8 @@ void led_trigger_register_simple(const char *name,
 				struct led_trigger **trigger);
 void led_trigger_unregister_simple(struct led_trigger *trigger);
 void led_trigger_event(struct led_trigger *trigger,  enum led_brightness event);
+void led_trigger_walk_leds(struct led_trigger *trig, led_trigger_walk_fn_t fn,
+			   void *data);
 void led_mc_trigger_event(struct led_trigger *trig,
 			  unsigned int *intensity_value, unsigned int num_colors,
 			  enum led_brightness brightness);
@@ -566,6 +571,8 @@ static inline void led_trigger_register_simple(const char *name,
 static inline void led_trigger_unregister_simple(struct led_trigger *trigger) {}
 static inline void led_trigger_event(struct led_trigger *trigger,
 				enum led_brightness event) {}
+static inline void led_trigger_walk_leds(struct led_trigger *trig,
+					 led_trigger_walk_fn_t fn, void *data) {}
 static inline void led_mc_trigger_event(struct led_trigger *trig,
 				unsigned int *intensity_value, unsigned int num_colors,
 				enum led_brightness brightness) {}

-- 
2.55.0