leds: trigger: Add led_trigger_notify_hw_control_changed() interface

Some hardware can autonomously activate/deactivate hardware control.
After that, the LED hardware notifies the LED driver. Currently, there
is no mechanism for LED drivers to notify the LED core about such events
and initiate a trigger transition to reflect the hardware state.

Add a new interface called led_trigger_notify_hw_control_changed(), so
that LED drivers can call it to notify the LED core about the
transition.

The interface only allows two transitions:

1. "none" => private trigger
2. private trigger => "none"

If the current trigger is neither the private trigger nor "none", no
transition will be made. This protects the currently selected software
trigger.

Note that LED_OFF won't be emitted during the #2 transition, as some
hardware may have selected a new brightness level during its hardware
state transition (e.g., laptop keyboards with a shortcut cycling through
different backlight brightnesses and auto mode).

The interface is designed as a void function as any failure should be
non-fatal and the result of transition should not have any impact on the
LED drivers' event handling procedures.

To use the interface, the config LEDS_TRIGGERS_HW_CHANGED must be
enabled, and the LED driver must set the LED_TRIG_HW_CHANGED flag for
the classdev.

By default, the config is enabled when LEDS_BRIGHTNESS_HW_CHANGED is
enabled.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20260921-leds-trigger-hw-changed-v7-10-fe3cdb6dec51@rong.moe
Signed-off-by: Lee Jones <lee@kernel.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/leds.h b/include/linux/leds.h
index 9a0bfd985b46..beaf23993063 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -109,6 +109,7 @@ struct led_classdev {
 #define LED_INIT_DEFAULT_TRIGGER BIT(23)
 #define LED_REJECT_NAME_CONFLICT BIT(24)
 #define LED_MULTI_COLOR		BIT(25)
+#define LED_TRIG_HW_CHANGED	BIT(26)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;
@@ -239,6 +240,11 @@ struct led_classdev {
 	struct kernfs_node	*brightness_hw_changed_kn;
 #endif
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+	bool			trigger_hw_changed;
+	struct work_struct	trigger_hw_changed_work;
+#endif
+
 	/* Ensures consistent access to the LED class device */
 	struct mutex		led_access;
 };
@@ -609,6 +615,13 @@ led_trigger_get_brightness(const struct led_trigger *trigger)
 
 #endif /* CONFIG_LEDS_TRIGGERS */
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+void led_trigger_notify_hw_control_changed(struct led_classdev *led_cdev, bool activate);
+#else
+static inline void led_trigger_notify_hw_control_changed(struct led_classdev *led_cdev,
+							 bool activate) {}
+#endif
+
 /* Trigger specific enum */
 enum led_trigger_netdev_modes {
 	TRIGGER_NETDEV_LINK = 0,