[PATCH v3 0/2] leds: trigger: input-events: Restore previous brightness on input

[PATCH v3 0/2] leds: trigger: input-events: Restore previous brightness on input

[Nikolay Plastinin via B4 Relay]

The input-events trigger turns LEDs back on with LED_FULL, so a keyboard
backlight with several levels always comes back at maximum after being
idle. This series restores the level the user picked instead.

Patch 1 adds led_trigger_for_each_led(), an RCU list iterator in leds.h.
Patch 2 uses it to save and restore each LED's brightness in one loop,
with per-LED state allocated in activate() and freed in deactivate().
There is no new exported function or callback API.

This came up while looking at a keyboard backlight idle timeout for ASUS
laptops in asusctl:
https://github.com/OpenGamingCollective/asusctl/issues/98

Tested on an ASUS ROG Flow X13 GV302XV (asus::kbd_backlight, 3 levels).
The trigger was built out of tree against Fedora 7.2.9-200.fc44.x86_64
with the modified leds.h and W=1. Brightness levels 1 and 2 were restored
after idle timeout and keyboard input. Twenty activate/deactivate cycles
completed, and no kernel messages appeared during the test. This was
not a full kernel build or a leak test.

LLM assistance was used to implement the review changes, prepare the
hardware test script, and draft the commit messages and this letter.
The hardware test was run locally by the submitter.

---
Changes in v3:
- Replace led_trigger_walk_leds() with led_trigger_for_each_led(), an
  RCU list iterator in include/linux/leds.h, as suggested by Lee Jones.
- Remove the exported helper, callback typedef, and void-pointer argument.
- Keep saving and restoring brightness in input_events_set_leds(), using
  guard(rcu)() and a single loop for both the on and off paths.
- Link to v2: https://lore.kernel.org/r/20260930-leds-input-events-brightness-v2-0-3948d3cddd83@gmail.com

Changes in v2:
- Keep the saved brightness in a per-LED struct allocated in activate()
  and freed in deactivate(), stored in led_cdev->trigger_data, instead of
  overloading blink_brightness (Lee Jones).
- Add led_trigger_walk_leds() to led-triggers.c and use it instead of
  walking led_cdevs/trig_list from the trigger (Lee Jones).
- Use the Assisted-by tag format from coding-assistants.rst.
- Link to v1: https://lore.kernel.org/r/20260924-leds-input-events-brightness-v1-1-b0ceff3a2343@gmail.com

---
Nikolay Plastinin (2):
      leds: triggers: Add led_trigger_for_each_led()
      leds: trigger: input-events: Restore previous brightness on input

 drivers/leds/trigger/ledtrig-input-events.c | 70 ++++++++++++++++++++++++++---
 include/linux/leds.h                        | 12 +++++
 2 files changed, 76 insertions(+), 6 deletions(-)
---
base-commit: f475845eaf3d749114a63270bf2efea459e14dd2
change-id: 20260924-leds-input-events-brightness-a76ae9a77b85

Best regards,
-- 
Nikolay Plastinin <plaztininikolai@gmail.com>

[PATCH v3 0/2] leds: trigger: input-events: Restore previous brightness on input

[Nikolay Plastinin]

The input-events trigger turns LEDs back on with LED_FULL, so a keyboard
backlight with several levels always comes back at maximum after being
idle. This series restores the level the user picked instead.

Patch 1 adds led_trigger_for_each_led(), an RCU list iterator in leds.h.
Patch 2 uses it to save and restore each LED's brightness in one loop,
with per-LED state allocated in activate() and freed in deactivate().
There is no new exported function or callback API.

This came up while looking at a keyboard backlight idle timeout for ASUS
laptops in asusctl:
https://github.com/OpenGamingCollective/asusctl/issues/98

Tested on an ASUS ROG Flow X13 GV302XV (asus::kbd_backlight, 3 levels).
The trigger was built out of tree against Fedora 7.2.9-200.fc44.x86_64
with the modified leds.h and W=1. Brightness levels 1 and 2 were restored
after idle timeout and keyboard input. Twenty activate/deactivate cycles
completed, and no kernel messages appeared during the test. This was
not a full kernel build or a leak test.

LLM assistance was used to implement the review changes, prepare the
hardware test script, and draft the commit messages and this letter.
The hardware test was run locally by the submitter.

---
Changes in v3:
- Replace led_trigger_walk_leds() with led_trigger_for_each_led(), an
  RCU list iterator in include/linux/leds.h, as suggested by Lee Jones.
- Remove the exported helper, callback typedef, and void-pointer argument.
- Keep saving and restoring brightness in input_events_set_leds(), using
  guard(rcu)() and a single loop for both the on and off paths.
- Link to v2: https://lore.kernel.org/r/20260930-leds-input-events-brightness-v2-0-3948d3cddd83@gmail.com

Changes in v2:
- Keep the saved brightness in a per-LED struct allocated in activate()
  and freed in deactivate(), stored in led_cdev->trigger_data, instead of
  overloading blink_brightness (Lee Jones).
- Add led_trigger_walk_leds() to led-triggers.c and use it instead of
  walking led_cdevs/trig_list from the trigger (Lee Jones).
- Use the Assisted-by tag format from coding-assistants.rst.
- Link to v1: https://lore.kernel.org/r/20260924-leds-input-events-brightness-v1-1-b0ceff3a2343@gmail.com

---
Nikolay Plastinin (2):
      leds: triggers: Add led_trigger_for_each_led()
      leds: trigger: input-events: Restore previous brightness on input

 drivers/leds/trigger/ledtrig-input-events.c | 70 ++++++++++++++++++++++++++---
 include/linux/leds.h                        | 12 +++++
 2 files changed, 76 insertions(+), 6 deletions(-)
---
base-commit: f475845eaf3d749114a63270bf2efea459e14dd2
change-id: 20260924-leds-input-events-brightness-a76ae9a77b85

Best regards,
-- 
Nikolay Plastinin <plaztininikolai@gmail.com>

[PATCH v3 1/2] leds: triggers: Add led_trigger_for_each_led()

[Nikolay Plastinin via B4 Relay]

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 needs to iterate
over the attached LEDs instead.

Add led_trigger_for_each_led(), a wrapper around list_for_each_entry_rcu(),
so triggers can perform this iteration without spelling out the list
members. Document that callers must hold the RCU read lock throughout
the iteration and must not sleep while accessing the LEDs.

Assisted-by: LLM
Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>
---
 include/linux/leds.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/leds.h b/include/linux/leds.h
index a515f075c..675c58661 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -11,6 +11,7 @@
 #include <dt-bindings/leds/common.h>
 #include <linux/device.h>
 #include <linux/mutex.h>
+#include <linux/rculist.h>
 #include <linux/rwsem.h>
 #include <linux/spinlock.h>
 #include <linux/timer.h>
@@ -502,6 +503,17 @@ struct led_trigger {
 	const struct attribute_group **groups;
 };
 
+/**
+ * led_trigger_for_each_led - iterate over the LEDs attached to a trigger
+ * @pos: struct led_classdev pointer used as the loop cursor
+ * @trig: trigger whose LEDs are iterated
+ *
+ * The caller must hold the RCU read lock throughout the iteration and must
+ * not sleep while accessing the LEDs.
+ */
+#define led_trigger_for_each_led(pos, trig) \
+	list_for_each_entry_rcu(pos, &(trig)->led_cdevs, trig_list)
+
 /*
  * Currently the attributes in struct led_trigger::groups are added directly to
  * the LED device. As this might change in the future, the following

-- 
2.56.0

[PATCH v3 1/2] leds: triggers: Add led_trigger_for_each_led()

[Nikolay Plastinin]

led_trigger_event() sets one brightness for all LEDs using a trigger.
A trigger which restores a different brightness per LED needs to iterate
over the attached LEDs instead.

Add led_trigger_for_each_led(), a wrapper around list_for_each_entry_rcu(),
so triggers can perform this iteration without spelling out the list
members. Document that callers must hold the RCU read lock throughout
the iteration and must not sleep while accessing the LEDs.

Assisted-by: LLM
Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>
---
 include/linux/leds.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/leds.h b/include/linux/leds.h
index a515f075c..675c58661 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -11,6 +11,7 @@
 #include <dt-bindings/leds/common.h>
 #include <linux/device.h>
 #include <linux/mutex.h>
+#include <linux/rculist.h>
 #include <linux/rwsem.h>
 #include <linux/spinlock.h>
 #include <linux/timer.h>
@@ -502,6 +503,17 @@ struct led_trigger {
 	const struct attribute_group **groups;
 };
 
+/**
+ * led_trigger_for_each_led - iterate over the LEDs attached to a trigger
+ * @pos: struct led_classdev pointer used as the loop cursor
+ * @trig: trigger whose LEDs are iterated
+ *
+ * The caller must hold the RCU read lock throughout the iteration and must
+ * not sleep while accessing the LEDs.
+ */
+#define led_trigger_for_each_led(pos, trig) \
+	list_for_each_entry_rcu(pos, &(trig)->led_cdevs, trig_list)
+
 /*
  * Currently the attributes in struct led_trigger::groups are added directly to
  * the LED device. As this might change in the future, the following

-- 
2.56.0

[PATCH v3 2/2] leds: trigger: input-events: Restore previous brightness on input

[Nikolay Plastinin via B4 Relay]

From: Nikolay Plastinin <plaztininikolai@gmail.com>

The trigger turns the LEDs back on with LED_FULL, which the LED core
clamps to max_brightness. For keyboard backlights with several levels,
such as asus::kbd_backlight, this means the backlight always comes back
at maximum after being idle instead of at the level the user picked.

Remember the brightness per LED before turning it off and restore it on
the next input event. Keep the level in a per-LED state struct allocated
in activate() and freed in deactivate(), converting the simple trigger
to a regular trigger. Pick up brightness changes made while the LED is
on before saving the level again.

Use led_trigger_for_each_led() under guard(rcu)() for both the on and off
paths. Skip LEDs whose activate() callback has not set up their state yet.

Tested on an ASUS ROG Flow X13 GV302XV: keyboard backlight levels 1 and 2
were restored after idle timeout and keyboard input, and 20 trigger
activate/deactivate cycles completed successfully.

Assisted-by: LLM
Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>
---
 drivers/leds/trigger/ledtrig-input-events.c | 70 ++++++++++++++++++++++++++---
 1 file changed, 64 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
index d057b2a23..b339f1e89 100644
--- a/drivers/leds/trigger/ledtrig-input-events.c
+++ b/drivers/leds/trigger/ledtrig-input-events.c
@@ -28,7 +28,63 @@ static struct input_events_data {
 	unsigned long led_off_time;
 } input_events_data;
 
-static struct led_trigger *input_events_led_trigger;
+struct input_events_led {
+	/* Brightness to restore on the next input event */
+	int brightness;
+};
+
+static int input_events_activate(struct led_classdev *led_cdev)
+{
+	struct input_events_data *data = &input_events_data;
+	struct input_events_led *led;
+	unsigned long flags;
+
+	led = kzalloc_obj(*led);
+	if (!led)
+		return -ENOMEM;
+
+	/* Start with the current brightness, or full if the LED is off */
+	led->brightness = led_cdev->brightness ?: led_cdev->max_brightness;
+
+	spin_lock_irqsave(&data->lock, flags);
+	led_set_trigger_data(led_cdev, led);
+	led_set_brightness(led_cdev, data->led_on ? led->brightness : LED_OFF);
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	return 0;
+}
+
+static void input_events_deactivate(struct led_classdev *led_cdev)
+{
+	kfree(led_get_trigger_data(led_cdev));
+}
+
+static struct led_trigger input_events_led_trigger = {
+	.name = "input-events",
+	.activate = input_events_activate,
+	.deactivate = input_events_deactivate,
+};
+
+/* Must be called with input_events_data.lock held */
+static void input_events_set_leds(bool on)
+{
+	struct led_classdev *led_cdev;
+
+	guard(rcu)();
+	led_trigger_for_each_led(led_cdev, &input_events_led_trigger) {
+		struct input_events_led *led = led_get_trigger_data(led_cdev);
+
+		/* Added to the trigger, but activate() has not run yet */
+		if (!led)
+			continue;
+
+		/* Preserve brightness changes made while the LED was on. */
+		if (led_cdev->brightness)
+			led->brightness = led_cdev->brightness;
+
+		led_set_brightness(led_cdev, on ? led->brightness : LED_OFF);
+	}
+}
 
 static void led_input_events_work(struct work_struct *work)
 {
@@ -42,7 +98,7 @@ static void led_input_events_work(struct work_struct *work)
 	 * running before a new event pushed led_off_time back.
 	 */
 	if (time_after_eq(jiffies, data->led_off_time)) {
-		led_trigger_event(input_events_led_trigger, LED_OFF);
+		input_events_set_leds(false);
 		data->led_on = false;
 	}
 
@@ -59,7 +115,7 @@ static void input_events_event(struct input_handle *handle, unsigned int type,
 	spin_lock_irqsave(&data->lock, flags);
 
 	if (!data->led_on) {
-		led_trigger_event(input_events_led_trigger, LED_FULL);
+		input_events_set_leds(true);
 		data->led_on = true;
 	}
 	data->led_off_time = jiffies + led_off_delay;
@@ -138,11 +194,13 @@ static int __init input_events_init(void)
 	INIT_DELAYED_WORK(&input_events_data.work, led_input_events_work);
 	spin_lock_init(&input_events_data.lock);
 
-	led_trigger_register_simple("input-events", &input_events_led_trigger);
+	ret = led_trigger_register(&input_events_led_trigger);
+	if (ret)
+		return ret;
 
 	ret = input_register_handler(&input_events_handler);
 	if (ret) {
-		led_trigger_unregister_simple(input_events_led_trigger);
+		led_trigger_unregister(&input_events_led_trigger);
 		return ret;
 	}
 
@@ -153,7 +211,7 @@ static void __exit input_events_exit(void)
 {
 	input_unregister_handler(&input_events_handler);
 	cancel_delayed_work_sync(&input_events_data.work);
-	led_trigger_unregister_simple(input_events_led_trigger);
+	led_trigger_unregister(&input_events_led_trigger);
 }
 
 module_init(input_events_init);

-- 
2.56.0

[PATCH v3 2/2] leds: trigger: input-events: Restore previous brightness on input

[Nikolay Plastinin]

The trigger turns the LEDs back on with LED_FULL, which the LED core
clamps to max_brightness. For keyboard backlights with several levels,
such as asus::kbd_backlight, this means the backlight always comes back
at maximum after being idle instead of at the level the user picked.

Remember the brightness per LED before turning it off and restore it on
the next input event. Keep the level in a per-LED state struct allocated
in activate() and freed in deactivate(), converting the simple trigger
to a regular trigger. Pick up brightness changes made while the LED is
on before saving the level again.

Use led_trigger_for_each_led() under guard(rcu)() for both the on and off
paths. Skip LEDs whose activate() callback has not set up their state yet.

Tested on an ASUS ROG Flow X13 GV302XV: keyboard backlight levels 1 and 2
were restored after idle timeout and keyboard input, and 20 trigger
activate/deactivate cycles completed successfully.

Assisted-by: LLM
Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>
---
 drivers/leds/trigger/ledtrig-input-events.c | 70 ++++++++++++++++++++++++++---
 1 file changed, 64 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
index d057b2a23..b339f1e89 100644
--- a/drivers/leds/trigger/ledtrig-input-events.c
+++ b/drivers/leds/trigger/ledtrig-input-events.c
@@ -28,7 +28,63 @@ static struct input_events_data {
 	unsigned long led_off_time;
 } input_events_data;
 
-static struct led_trigger *input_events_led_trigger;
+struct input_events_led {
+	/* Brightness to restore on the next input event */
+	int brightness;
+};
+
+static int input_events_activate(struct led_classdev *led_cdev)
+{
+	struct input_events_data *data = &input_events_data;
+	struct input_events_led *led;
+	unsigned long flags;
+
+	led = kzalloc_obj(*led);
+	if (!led)
+		return -ENOMEM;
+
+	/* Start with the current brightness, or full if the LED is off */
+	led->brightness = led_cdev->brightness ?: led_cdev->max_brightness;
+
+	spin_lock_irqsave(&data->lock, flags);
+	led_set_trigger_data(led_cdev, led);
+	led_set_brightness(led_cdev, data->led_on ? led->brightness : LED_OFF);
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	return 0;
+}
+
+static void input_events_deactivate(struct led_classdev *led_cdev)
+{
+	kfree(led_get_trigger_data(led_cdev));
+}
+
+static struct led_trigger input_events_led_trigger = {
+	.name = "input-events",
+	.activate = input_events_activate,
+	.deactivate = input_events_deactivate,
+};
+
+/* Must be called with input_events_data.lock held */
+static void input_events_set_leds(bool on)
+{
+	struct led_classdev *led_cdev;
+
+	guard(rcu)();
+	led_trigger_for_each_led(led_cdev, &input_events_led_trigger) {
+		struct input_events_led *led = led_get_trigger_data(led_cdev);
+
+		/* Added to the trigger, but activate() has not run yet */
+		if (!led)
+			continue;
+
+		/* Preserve brightness changes made while the LED was on. */
+		if (led_cdev->brightness)
+			led->brightness = led_cdev->brightness;
+
+		led_set_brightness(led_cdev, on ? led->brightness : LED_OFF);
+	}
+}
 
 static void led_input_events_work(struct work_struct *work)
 {
@@ -42,7 +98,7 @@ static void led_input_events_work(struct work_struct *work)
 	 * running before a new event pushed led_off_time back.
 	 */
 	if (time_after_eq(jiffies, data->led_off_time)) {
-		led_trigger_event(input_events_led_trigger, LED_OFF);
+		input_events_set_leds(false);
 		data->led_on = false;
 	}
 
@@ -59,7 +115,7 @@ static void input_events_event(struct input_handle *handle, unsigned int type,
 	spin_lock_irqsave(&data->lock, flags);
 
 	if (!data->led_on) {
-		led_trigger_event(input_events_led_trigger, LED_FULL);
+		input_events_set_leds(true);
 		data->led_on = true;
 	}
 	data->led_off_time = jiffies + led_off_delay;
@@ -138,11 +194,13 @@ static int __init input_events_init(void)
 	INIT_DELAYED_WORK(&input_events_data.work, led_input_events_work);
 	spin_lock_init(&input_events_data.lock);
 
-	led_trigger_register_simple("input-events", &input_events_led_trigger);
+	ret = led_trigger_register(&input_events_led_trigger);
+	if (ret)
+		return ret;
 
 	ret = input_register_handler(&input_events_handler);
 	if (ret) {
-		led_trigger_unregister_simple(input_events_led_trigger);
+		led_trigger_unregister(&input_events_led_trigger);
 		return ret;
 	}
 
@@ -153,7 +211,7 @@ static void __exit input_events_exit(void)
 {
 	input_unregister_handler(&input_events_handler);
 	cancel_delayed_work_sync(&input_events_data.work);
-	led_trigger_unregister_simple(input_events_led_trigger);
+	led_trigger_unregister(&input_events_led_trigger);
 }
 
 module_init(input_events_init);

-- 
2.56.0

Re: [PATCH v3 1/2] leds: triggers: Add led_trigger_for_each_led()

[sashiko-bot]

> 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 needs to iterate
> over the attached LEDs instead.
> 
> Add led_trigger_for_each_led(), a wrapper around list_for_each_entry_rcu(),
> so triggers can perform this iteration without spelling out the list
> members. Document that callers must hold the RCU read lock throughout
> the iteration and must not sleep while accessing the LEDs.
> 
> Assisted-by: LLM
> Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016-leds-input-events-brightness-v3-0-2c462cafe020@gmail.com?part=1

Re: [PATCH v3 2/2] leds: trigger: input-events: Restore previous brightness on input

[sashiko-bot]

> From: Nikolay Plastinin <plaztininikolai@gmail.com>
> 
> The trigger turns the LEDs back on with LED_FULL, which the LED core
> clamps to max_brightness. For keyboard backlights with several levels,
> such as asus::kbd_backlight, this means the backlight always comes back
> at maximum after being idle instead of at the level the user picked.
> 
> Remember the brightness per LED before turning it off and restore it on
> the next input event. Keep the level in a per-LED state struct allocated
> in activate() and freed in deactivate(), converting the simple trigger
> to a regular trigger. Pick up brightness changes made while the LED is
> on before saving the level again.
> 
> Use led_trigger_for_each_led() under guard(rcu)() for both the on and off
> paths. Skip LEDs whose activate() callback has not set up their state yet.
> 
> Tested on an ASUS ROG Flow X13 GV302XV: keyboard backlight levels 1 and 2
> were restored after idle timeout and keyboard input, and 20 trigger
> activate/deactivate cycles completed successfully.
> 
> Assisted-by: LLM
> Signed-off-by: Nikolay Plastinin <plaztininikolai@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016-leds-input-events-brightness-v3-0-2c462cafe020@gmail.com?part=2