backlight: Remove notifier

backlight_register_notifier and backlight_unregister_notifier have
been unused since commit 6cb634d ("ACPI: video: Remove code to
unregister acpi_video backlight when a native backlight registers")

With those not being called, it means that the backlight_notifier
list is always empty.

Remove the functions, the list itself and the enum used in the
notifications.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20240919232758.639925-1-linux@treblig.org
Signed-off-by: Lee Jones <lee@kernel.org>

Author: Dr. David Alan Gilbert

drivers/video/backlight/backlight.c

@@ -65,7 +65,6 @@
 
 static struct list_head backlight_dev_list;
 static struct mutex backlight_dev_list_mutex;
-static struct blocking_notifier_head backlight_notifier;
 
 static const char *const backlight_types[] = {
 	[BACKLIGHT_RAW] = "raw",
@@ -467,9 +466,6 @@ struct backlight_device *backlight_device_register(const char *name,
 	list_add(&new_bd->entry, &backlight_dev_list);
 	mutex_unlock(&backlight_dev_list_mutex);
 
-	blocking_notifier_call_chain(&backlight_notifier,
-				     BACKLIGHT_REGISTERED, new_bd);
-
 	return new_bd;
 }
 EXPORT_SYMBOL(backlight_device_register);
@@ -539,9 +535,6 @@ void backlight_device_unregister(struct backlight_device *bd)
 	mutex_unlock(&pmac_backlight_mutex);
 #endif
 
-	blocking_notifier_call_chain(&backlight_notifier,
-				     BACKLIGHT_UNREGISTERED, bd);
-
 	mutex_lock(&bd->ops_lock);
 	bd->ops = NULL;
 	mutex_unlock(&bd->ops_lock);
@@ -566,40 +559,6 @@ static int devm_backlight_device_match(struct device *dev, void *res,
 	return *r == data;
 }
 
-/**
- * backlight_register_notifier - get notified of backlight (un)registration
- * @nb: notifier block with the notifier to call on backlight (un)registration
- *
- * Register a notifier to get notified when backlight devices get registered
- * or unregistered.
- *
- * RETURNS:
- *
- * 0 on success, otherwise a negative error code
- */
-int backlight_register_notifier(struct notifier_block *nb)
-{
-	return blocking_notifier_chain_register(&backlight_notifier, nb);
-}
-EXPORT_SYMBOL(backlight_register_notifier);
-
-/**
- * backlight_unregister_notifier - unregister a backlight notifier
- * @nb: notifier block to unregister
- *
- * Register a notifier to get notified when backlight devices get registered
- * or unregistered.
- *
- * RETURNS:
- *
- * 0 on success, otherwise a negative error code
- */
-int backlight_unregister_notifier(struct notifier_block *nb)
-{
-	return blocking_notifier_chain_unregister(&backlight_notifier, nb);
-}
-EXPORT_SYMBOL(backlight_unregister_notifier);
-
 /**
  * devm_backlight_device_register - register a new backlight device
  * @dev: the device to register
@@ -767,7 +726,6 @@ static int __init backlight_class_init(void)
 
 	INIT_LIST_HEAD(&backlight_dev_list);
 	mutex_init(&backlight_dev_list_mutex);
-	BLOCKING_INIT_NOTIFIER_HEAD(&backlight_notifier);
 
 	return 0;
 }

include/linux/backlight.h

@@ -66,24 +66,6 @@ enum backlight_type {
 	BACKLIGHT_TYPE_MAX,
 };
 
-/**
- * enum backlight_notification - the type of notification
- *
- * The notifications that is used for notification sent to the receiver
- * that registered notifications using backlight_register_notifier().
- */
-enum backlight_notification {
-	/**
-	 * @BACKLIGHT_REGISTERED: The backlight device is registered.
-	 */
-	BACKLIGHT_REGISTERED,
-
-	/**
-	 * @BACKLIGHT_UNREGISTERED: The backlight revice is unregistered.
-	 */
-	BACKLIGHT_UNREGISTERED,
-};
-
 /** enum backlight_scale - the type of scale used for brightness values
  *
  * The type of scale used for brightness values.
@@ -421,8 +403,6 @@ void devm_backlight_device_unregister(struct device *dev,
 				      struct backlight_device *bd);
 void backlight_force_update(struct backlight_device *bd,
 			    enum backlight_update_reason reason);
-int backlight_register_notifier(struct notifier_block *nb);
-int backlight_unregister_notifier(struct notifier_block *nb);
 struct backlight_device *backlight_device_get_by_name(const char *name);
 struct backlight_device *backlight_device_get_by_type(enum backlight_type type);
 int backlight_device_set_brightness(struct backlight_device *bd,