platform/x86: asus-wmi: add keyboard brightness event handler

The keyboard brightness control of Asus WMI keyboards is handled in
kernel, which leads to the shortcut going from brightness 0, to 1,
to 2, and 3.

However, for HID keyboards it is exposed as a key and handled by the
user's desktop environment. For the toggle button, this means that
brightness control becomes on/off. In addition, in the absence of a
DE, the keyboard brightness does not work.

Therefore, expose an event handler for the keyboard brightness control
which can then be used by hid-asus. Since this handler is called from
an interrupt context, defer the actual work to a workqueue.

In the process, introduce ASUS_EV_MAX_BRIGHTNESS to hold the constant
for maximum brightness since it is shared between hid-asus/asus-wmi.

Reviewed-by: Luke D. Jones <luke@ljones.dev>
Tested-by: Luke D. Jones <luke@ljones.dev>
Acked-by: Benjamin Tissoires <bentiss@kernel.org>
Reviewed-by: Denis Benato <benato.denis96@gmail.com>
Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
Link: https://patch.msgid.link/20260122075044.5070-11-lkml@antheas.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: antheas

drivers/platform/x86/asus-wmi.c

@@ -1719,6 +1719,44 @@ static void kbd_led_update_all(struct work_struct *work)
 	}
 }
 
+/*
+ * This function is called from hid-asus to inform asus-wmi of brightness
+ * changes initiated by the keyboard backlight keys.
+ */
+int asus_hid_event(enum asus_hid_event event)
+{
+	struct asus_wmi *asus;
+	int brightness;
+
+	guard(spinlock_irqsave)(&asus_ref.lock);
+	asus = asus_ref.asus;
+	if (!asus || !asus->kbd_led_registered)
+		return -EBUSY;
+
+	brightness = asus->kbd_led_wk;
+
+	switch (event) {
+	case ASUS_EV_BRTUP:
+		brightness += 1;
+		break;
+	case ASUS_EV_BRTDOWN:
+		brightness -= 1;
+		break;
+	case ASUS_EV_BRTTOGGLE:
+		if (brightness >= ASUS_EV_MAX_BRIGHTNESS)
+			brightness = 0;
+		else
+			brightness += 1;
+		break;
+	}
+
+	asus->kbd_led_wk = clamp_val(brightness, 0, ASUS_EV_MAX_BRIGHTNESS);
+	asus->kbd_led_notify = true;
+	queue_work(asus->led_workqueue, &asus->kbd_led_work);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(asus_hid_event);
+
 /*
  * These functions actually update the LED's, and are called from a
  * workqueue. By doing this as separate work rather than when the LED
@@ -1801,13 +1839,11 @@ static void do_kbd_led_set(struct led_classdev *led_cdev, int value)
 {
 	struct asus_hid_listener *listener;
 	struct asus_wmi *asus;
-	int max_level;
 
 	asus = container_of(led_cdev, struct asus_wmi, kbd_led);
-	max_level = asus->kbd_led.max_brightness;
 
 	scoped_guard(spinlock_irqsave, &asus_ref.lock)
-		asus->kbd_led_wk = clamp_val(value, 0, max_level);
+		asus->kbd_led_wk = clamp_val(value, 0, ASUS_EV_MAX_BRIGHTNESS);
 
 	if (asus->kbd_led_avail)
 		kbd_led_update(asus);
@@ -2011,7 +2047,7 @@ static int asus_wmi_led_init(struct asus_wmi *asus)
 	asus->kbd_led.flags = LED_BRIGHT_HW_CHANGED;
 	asus->kbd_led.brightness_set_blocking = kbd_led_set;
 	asus->kbd_led.brightness_get = kbd_led_get;
-	asus->kbd_led.max_brightness = 3;
+	asus->kbd_led.max_brightness = ASUS_EV_MAX_BRIGHTNESS;
 	asus->kbd_led_avail = !kbd_led_read(asus, &led_val, NULL);
 	INIT_WORK(&asus->kbd_led_work, kbd_led_update_all);
 
@@ -4530,7 +4566,7 @@ static void asus_wmi_handle_event_code(int code, struct asus_wmi *asus)
 		return;
 	}
 	if (code == NOTIFY_KBD_BRTTOGGLE) {
-		if (led_value >= asus->kbd_led.max_brightness)
+		if (led_value >= ASUS_EV_MAX_BRIGHTNESS)
 			kbd_led_set_by_kbd(asus, 0);
 		else
 			kbd_led_set_by_kbd(asus, led_value + 1);

include/linux/platform_data/x86/asus-wmi.h

@@ -178,6 +178,14 @@ struct asus_hid_listener {
 	void (*brightness_set)(struct asus_hid_listener *listener, int brightness);
 };
 
+enum asus_hid_event {
+	ASUS_EV_BRTUP,
+	ASUS_EV_BRTDOWN,
+	ASUS_EV_BRTTOGGLE,
+};
+
+#define ASUS_EV_MAX_BRIGHTNESS 3
+
 #if IS_REACHABLE(CONFIG_ASUS_WMI)
 void set_ally_mcu_hack(enum asus_ally_mcu_hack status);
 void set_ally_mcu_powersave(bool enabled);
@@ -186,6 +194,7 @@ int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param, u32 *retval);
 int asus_wmi_evaluate_method(u32 method_id, u32 arg0, u32 arg1, u32 *retval);
 int asus_hid_register_listener(struct asus_hid_listener *cdev);
 void asus_hid_unregister_listener(struct asus_hid_listener *cdev);
+int asus_hid_event(enum asus_hid_event event);
 #else
 static inline void set_ally_mcu_hack(enum asus_ally_mcu_hack status)
 {
@@ -213,6 +222,10 @@ static inline int asus_hid_register_listener(struct asus_hid_listener *bdev)
 static inline void asus_hid_unregister_listener(struct asus_hid_listener *bdev)
 {
 }
+static inline int asus_hid_event(enum asus_hid_event event)
+{
+	return -ENODEV;
+}
 #endif
 
 #endif	/* __PLATFORM_DATA_X86_ASUS_WMI_H */