[PATCH v5] leds: trigger: input-events: Restore previous brightness on input

[PATCH v5] 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.

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

Clear trigger_data under the same lock used by the LED walker before
freeing the per-LED state. Although normal trigger removal waits for an
RCU grace period, the device_add_groups() error path calls deactivate()
while the LED is still linked, so a walker must see NULL after teardown.

The previous revision was 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>
---
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.

V5 is a single patch. Iterate directly over the trigger's LEDs using
list_for_each_entry_rcu() under guard(rcu)(), as requested by Greg KH.
The per-LED state and locked teardown from v4 are unchanged. No changes
to include/linux/leds.h or the LED core are needed.

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

Validation for v5: the module builds out of tree with W=1 against Fedora
7.2.12-200.fc44.x86_64 using the installed kernel headers. The user-space
harness using the driver functions passes ASan/UBSan for the error-unwind
ordering, brightness restoration, and 10,000 concurrent teardown cycles.
The harness uses a mutex and a one-element list instead of kernel
primitives; it is not kernel fault injection or an RCU implementation test.
V5 hardware testing passed on the GV302XV with kernel 7.2.12: levels 1
and 2 were restored after idle and input, and 20 activate/deactivate
cycles completed. The original brightness 2 and trigger none were
restored, and the test module was unloaded. A separate journalctl check
of the test interval showed no kernel entries; the script's dmesg output
included messages from earlier suspend/resume cycles.

V4 was tested on an ASUS ROG Flow X13 GV302XV with kernel
7.2.12-200.fc44.x86_64 and no external monitor: brightness levels 1 and 2
were restored after idle timeout and keyboard input, and 20 trigger
activate/deactivate cycles passed. No kernel messages appeared during
the test. The original brightness and trigger were restored afterwards.
No full kernel build has been performed.

LLM assistance was used for the implementation, tests and message drafts.
---
Changes in v5:
- Drop the common led_trigger_for_each_led() macro and its patch.
- Open-code list_for_each_entry_rcu() next to guard(rcu)() in the trigger,
  as requested by Greg KH; include linux/rculist.h directly.
- Keep the locked trigger_data teardown from v4 unchanged.
- Link to v4: https://lore.kernel.org/r/20261030-leds-input-events-brightness-v4-0-5ea0ead7480c@gmail.com

Changes in v4:
- Clear trigger_data under input_events_data.lock before freeing per-LED
  state in deactivate(), as suggested by Lee Jones. This also covers the
  device_add_groups() error path, which deactivates before list removal.
- Update the NULL-state comment to cover activation error unwind.
- Patch 1 is unchanged.
- Link to v3: https://lore.kernel.org/r/20261016-leds-input-events-brightness-v3-0-2c462cafe020@gmail.com

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
---
 drivers/leds/trigger/ledtrig-input-events.c | 78 ++++++++++++++++++++++++++---
 1 file changed, 72 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
index d057b2a23..5fbd3e853 100644
--- a/drivers/leds/trigger/ledtrig-input-events.c
+++ b/drivers/leds/trigger/ledtrig-input-events.c
@@ -10,6 +10,7 @@
 #include <linux/leds.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
+#include <linux/rculist.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/workqueue.h>
@@ -28,7 +29,70 @@ 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)
+{
+	struct input_events_led *led;
+
+	scoped_guard(spinlock_irqsave, &input_events_data.lock) {
+		led = led_get_trigger_data(led_cdev);
+		led_set_trigger_data(led_cdev, NULL);
+	}
+	kfree(led);
+}
+
+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)();
+	list_for_each_entry_rcu(led_cdev, &input_events_led_trigger.led_cdevs,
+				trig_list) {
+		struct input_events_led *led = led_get_trigger_data(led_cdev);
+
+		/* Not yet activated, or already deactivated during error unwind */
+		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 +106,7 @@ 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 +123,7 @@ 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 +202,13 @@ 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 +219,7 @@ 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);

---
base-commit: f475845eaf3d749114a63270bf2efea459e14dd2
change-id: 20260924-leds-input-events-brightness-a76ae9a77b85

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

Re: [PATCH v5] leds: trigger: input-events: Restore previous brightness on input

[Greg Kroah-Hartman]

On Sun, Nov 01, 2026 at 03:19:18PM +0800, Nikolay Plastinin via B4 Relay wrote:
> 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.
> 
> Iterate directly with list_for_each_entry_rcu() under guard(rcu)() for
> both the on and off paths. Skip LEDs whose activate() callback has not
> set up their state yet.

That says what you are doing, but not _WHY_ you are doing it.  Why is
rcu needed here?  That feels very odd for something like a LED, why
isn't the normal device lifetime rules applicable here which would
require RCU to somehow be added just for this?

> Clear trigger_data under the same lock used by the LED walker before
> freeing the per-LED state. Although normal trigger removal waits for an
> RCU grace period, the device_add_groups() error path calls deactivate()
> while the LED is still linked, so a walker must see NULL after teardown.

This is obviously LLM generated, please start from scratch and rewrite
this whole changelog on your own.

> The previous revision was 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>
> ---
> 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.
> 
> V5 is a single patch. Iterate directly over the trigger's LEDs using
> list_for_each_entry_rcu() under guard(rcu)(), as requested by Greg KH.
> The per-LED state and locked teardown from v4 are unchanged. No changes
> to include/linux/leds.h or the LED core are needed.
> 
> This came up while looking at a keyboard backlight idle timeout for ASUS
> laptops in asusctl:
> https://github.com/OpenGamingCollective/asusctl/issues/98
> 
> Validation for v5: the module builds out of tree with W=1 against Fedora
> 7.2.12-200.fc44.x86_64 using the installed kernel headers. The user-space
> harness using the driver functions passes ASan/UBSan for the error-unwind
> ordering, brightness restoration, and 10,000 concurrent teardown cycles.
> The harness uses a mutex and a one-element list instead of kernel
> primitives; it is not kernel fault injection or an RCU implementation test.
> V5 hardware testing passed on the GV302XV with kernel 7.2.12: levels 1
> and 2 were restored after idle and input, and 20 activate/deactivate
> cycles completed. The original brightness 2 and trigger none were
> restored, and the test module was unloaded. A separate journalctl check
> of the test interval showed no kernel entries; the script's dmesg output
> included messages from earlier suspend/resume cycles.
> 
> V4 was tested on an ASUS ROG Flow X13 GV302XV with kernel
> 7.2.12-200.fc44.x86_64 and no external monitor: brightness levels 1 and 2
> were restored after idle timeout and keyboard input, and 20 trigger
> activate/deactivate cycles passed. No kernel messages appeared during
> the test. The original brightness and trigger were restored afterwards.
> No full kernel build has been performed.
> 
> LLM assistance was used for the implementation, tests and message drafts.
> ---
> Changes in v5:
> - Drop the common led_trigger_for_each_led() macro and its patch.
> - Open-code list_for_each_entry_rcu() next to guard(rcu)() in the trigger,
>   as requested by Greg KH; include linux/rculist.h directly.
> - Keep the locked trigger_data teardown from v4 unchanged.
> - Link to v4: https://lore.kernel.org/r/20261030-leds-input-events-brightness-v4-0-5ea0ead7480c@gmail.com
> 
> Changes in v4:
> - Clear trigger_data under input_events_data.lock before freeing per-LED
>   state in deactivate(), as suggested by Lee Jones. This also covers the
>   device_add_groups() error path, which deactivates before list removal.
> - Update the NULL-state comment to cover activation error unwind.
> - Patch 1 is unchanged.
> - Link to v3: https://lore.kernel.org/r/20261016-leds-input-events-brightness-v3-0-2c462cafe020@gmail.com
> 
> 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
> ---
>  drivers/leds/trigger/ledtrig-input-events.c | 78 ++++++++++++++++++++++++++---
>  1 file changed, 72 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
> index d057b2a23..5fbd3e853 100644
> --- a/drivers/leds/trigger/ledtrig-input-events.c
> +++ b/drivers/leds/trigger/ledtrig-input-events.c
> @@ -10,6 +10,7 @@
>  #include <linux/leds.h>
>  #include <linux/module.h>
>  #include <linux/moduleparam.h>
> +#include <linux/rculist.h>
>  #include <linux/slab.h>
>  #include <linux/spinlock.h>
>  #include <linux/workqueue.h>
> @@ -28,7 +29,70 @@ 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)
> +{
> +	struct input_events_led *led;
> +
> +	scoped_guard(spinlock_irqsave, &input_events_data.lock) {
> +		led = led_get_trigger_data(led_cdev);
> +		led_set_trigger_data(led_cdev, NULL);
> +	}
> +	kfree(led);
> +}
> +
> +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 */

Great, then add the proper static checking for this state so that the
tools catch it when someone does not do that.

> +static void input_events_set_leds(bool on)

"set" and "on"?  Naming is hard :)

Look at how this is used:

> +{
> +	struct led_classdev *led_cdev;
> +
> +	guard(rcu)();
> +	list_for_each_entry_rcu(led_cdev, &input_events_led_trigger.led_cdevs,
> +				trig_list) {
> +		struct input_events_led *led = led_get_trigger_data(led_cdev);
> +
> +		/* Not yet activated, or already deactivated during error unwind */
> +		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 +106,7 @@ 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);

"Set" and "false"?  So you don't want to set anything?

Again, naming is hard, the original code here was obvious what was
happening, LED_OFF is self-describing.  Your change is now not that.

thanks,

greg k-h