leds: backlight trigger: Replace fb events with a dedicated function call

Remove support for fb events from the led backlight trigger. Provide
the helper ledtrig_backlight_blank() instead. Call it from fbdev to
inform the trigger of changes to a display's blank state.

Fbdev maintains a list of all installed notifiers. Instead of the fbdev
notifiers, maintain an internal list of led backlight triggers.

v3:
- export ledtrig_backlight_blank()
v2:
- maintain global list of led backlight triggers (Lee)
- avoid IS_REACHABLE() in source file (Lee)
- notify on changes to blank state instead of display state
- use lock guards
- initialize led list and list mutex

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20250321095517.313713-11-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>

Author: Thomas Zimmermann

drivers/leds/trigger/ledtrig-backlight.c

@@ -10,7 +10,6 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/init.h>
-#include <linux/fb.h>
 #include <linux/leds.h>
 #include "../leds.h"
 
@@ -21,10 +20,14 @@ struct bl_trig_notifier {
 	struct led_classdev *led;
 	int brightness;
 	int old_status;
-	struct notifier_block notifier;
 	unsigned invert;
+
+	struct list_head entry;
 };
 
+static DEFINE_MUTEX(ledtrig_backlight_list_mutex);
+static LIST_HEAD(ledtrig_backlight_list);
+
 static void ledtrig_backlight_notify_blank(struct bl_trig_notifier *n, int new_status)
 {
 	struct led_classdev *led = n->led;
@@ -42,26 +45,17 @@ static void ledtrig_backlight_notify_blank(struct bl_trig_notifier *n, int new_s
 	n->old_status = new_status;
 }
 
-static int fb_notifier_callback(struct notifier_block *p,
-				unsigned long event, void *data)
+void ledtrig_backlight_blank(bool blank)
 {
-	struct bl_trig_notifier *n = container_of(p,
-					struct bl_trig_notifier, notifier);
-	struct fb_event *fb_event = data;
-	int *blank;
-	int new_status;
-
-	/* If we aren't interested in this event, skip it immediately ... */
-	if (event != FB_EVENT_BLANK)
-		return 0;
-
-	blank = fb_event->data;
-	new_status = *blank ? BLANK : UNBLANK;
+	struct bl_trig_notifier *n;
+	int new_status = blank ? BLANK : UNBLANK;
 
-	ledtrig_backlight_notify_blank(n, new_status);
+	guard(mutex)(&ledtrig_backlight_list_mutex);
 
-	return 0;
+	list_for_each_entry(n, &ledtrig_backlight_list, entry)
+		ledtrig_backlight_notify_blank(n, new_status);
 }
+EXPORT_SYMBOL(ledtrig_backlight_blank);
 
 static ssize_t bl_trig_invert_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
@@ -106,8 +100,6 @@ ATTRIBUTE_GROUPS(bl_trig);
 
 static int bl_trig_activate(struct led_classdev *led)
 {
-	int ret;
-
 	struct bl_trig_notifier *n;
 
 	n = kzalloc(sizeof(struct bl_trig_notifier), GFP_KERNEL);
@@ -118,11 +110,9 @@ static int bl_trig_activate(struct led_classdev *led)
 	n->led = led;
 	n->brightness = led->brightness;
 	n->old_status = UNBLANK;
-	n->notifier.notifier_call = fb_notifier_callback;
 
-	ret = fb_register_client(&n->notifier);
-	if (ret)
-		dev_err(led->dev, "unable to register backlight trigger\n");
+	guard(mutex)(&ledtrig_backlight_list_mutex);
+	list_add(&n->entry, &ledtrig_backlight_list);
 
 	return 0;
 }
@@ -131,7 +121,9 @@ static void bl_trig_deactivate(struct led_classdev *led)
 {
 	struct bl_trig_notifier *n = led_get_trigger_data(led);
 
-	fb_unregister_client(&n->notifier);
+	guard(mutex)(&ledtrig_backlight_list_mutex);
+	list_del(&n->entry);
+
 	kfree(n);
 }
 

drivers/video/fbdev/core/fbmem.c

@@ -16,6 +16,7 @@
 #include <linux/fb.h>
 #include <linux/fbcon.h>
 #include <linux/lcd.h>
+#include <linux/leds.h>
 
 #include <video/nomodeset.h>
 
@@ -369,11 +370,17 @@ static void fb_lcd_notify_blank(struct fb_info *info)
 	lcd_notify_blank_all(info->device, power);
 }
 
+static void fb_ledtrig_backlight_notify_blank(struct fb_info *info)
+{
+	if (info->blank == FB_BLANK_UNBLANK)
+		ledtrig_backlight_blank(false);
+	else
+		ledtrig_backlight_blank(true);
+}
+
 int fb_blank(struct fb_info *info, int blank)
 {
 	int old_blank = info->blank;
-	struct fb_event event;
-	int data[2];
 	int ret;
 
 	if (!info->fbops->fb_blank)
@@ -382,11 +389,6 @@ int fb_blank(struct fb_info *info, int blank)
 	if (blank > FB_BLANK_POWERDOWN)
 		blank = FB_BLANK_POWERDOWN;
 
-	data[0] = blank;
-	data[1] = old_blank;
-	event.info = info;
-	event.data = data;
-
 	info->blank = blank;
 
 	ret = info->fbops->fb_blank(blank, info);
@@ -395,8 +397,7 @@ int fb_blank(struct fb_info *info, int blank)
 
 	fb_bl_notify_blank(info, old_blank);
 	fb_lcd_notify_blank(info);
-
-	fb_notifier_call_chain(FB_EVENT_BLANK, &event);
+	fb_ledtrig_backlight_notify_blank(info);
 
 	return 0;
 

include/linux/leds.h

@@ -640,6 +640,12 @@ static inline void ledtrig_flash_ctrl(bool on) {}
 static inline void ledtrig_torch_ctrl(bool on) {}
 #endif
 
+#if IS_REACHABLE(CONFIG_LEDS_TRIGGER_BACKLIGHT)
+void ledtrig_backlight_blank(bool blank);
+#else
+static inline void ledtrig_backlight_blank(bool blank) {}
+#endif
+
 /*
  * Generic LED platform data for describing LED names and default triggers.
  */