backlight: Move blank-state handling into helper

Move the handling of blank-state updates into a separate helper,
so that is can be called without the fbdev event. No functional
changes.

As a minor improvement over the original code, the update replaces
manual locking with a guard.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: "Daniel Thompson (RISCstar)" <danielt@kernel.org>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20250321095517.313713-6-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>

Author: Thomas Zimmermann

drivers/video/backlight/backlight.c

@@ -80,6 +80,30 @@ static const char *const backlight_scale_types[] = {
 
 #if defined(CONFIG_FB_CORE) || (defined(CONFIG_FB_CORE_MODULE) && \
 				defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
+static void backlight_notify_blank(struct backlight_device *bd,
+				   struct device *display_dev,
+				   bool fb_on, bool prev_fb_on)
+{
+	guard(mutex)(&bd->ops_lock);
+
+	if (!bd->ops)
+		return;
+	if (bd->ops->controls_device && !bd->ops->controls_device(bd, display_dev))
+		return;
+
+	if (fb_on && (!prev_fb_on || !bd->use_count)) {
+		if (!bd->use_count++) {
+			bd->props.state &= ~BL_CORE_FBBLANK;
+			backlight_update_status(bd);
+		}
+	} else if (!fb_on && prev_fb_on && bd->use_count) {
+		if (!(--bd->use_count)) {
+			bd->props.state |= BL_CORE_FBBLANK;
+			backlight_update_status(bd);
+		}
+	}
+}
+
 /*
  * fb_notifier_callback
  *
@@ -107,31 +131,15 @@ static int fb_notifier_callback(struct notifier_block *self,
 		return 0;
 
 	bd = container_of(self, struct backlight_device, fb_notif);
-	mutex_lock(&bd->ops_lock);
 
-	if (!bd->ops)
-		goto out;
-	if (bd->ops->controls_device && !bd->ops->controls_device(bd, info->device))
-		goto out;
 	if (fb_bd && fb_bd != bd)
-		goto out;
+		return 0;
 
 	fb_on = fb_blank[0] == FB_BLANK_UNBLANK;
 	prev_fb_on = fb_blank[1] == FB_BLANK_UNBLANK;
 
-	if (fb_on && (!prev_fb_on || !bd->use_count)) {
-		if (!bd->use_count++) {
-			bd->props.state &= ~BL_CORE_FBBLANK;
-			backlight_update_status(bd);
-		}
-	} else if (!fb_on && prev_fb_on && bd->use_count) {
-		if (!(--bd->use_count)) {
-			bd->props.state |= BL_CORE_FBBLANK;
-			backlight_update_status(bd);
-		}
-	}
-out:
-	mutex_unlock(&bd->ops_lock);
+	backlight_notify_blank(bd, info->device, fb_on, prev_fb_on);
+
 	return 0;
 }