ACPI / video: Don't register acpi_video_resume notifier without backlight devices

If we're not going to be registering any backlight devices then
acpi_video_resume is always nop, so don't register it in that case.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/video.c

@@ -150,6 +150,7 @@ struct acpi_video_enumerated_device {
 
 struct acpi_video_bus {
 	struct acpi_device *device;
+	bool backlight_registered;
 	u8 dos_setting;
 	struct acpi_video_enumerated_device *attached_array;
 	u8 attached_count;
@@ -1666,7 +1667,6 @@ acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
 
 static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 {
-	if (acpi_video_verify_backlight_support()) {
 	struct backlight_properties props;
 	struct pci_dev *pdev;
 	acpi_handle acpi_parent;
@@ -1714,11 +1714,9 @@ static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 				device->dev, &video_cooling_ops);
 	if (IS_ERR(device->cooling_dev)) {
 		/*
-			 * Set cooling_dev to NULL so we don't crash trying to
-			 * free it.
-			 * Also, why the hell we are returning early and
-			 * not attempt to register video output if cooling
-			 * device registration failed?
+		 * Set cooling_dev to NULL so we don't crash trying to free it.
+		 * Also, why the hell we are returning early and not attempt to
+		 * register video output if cooling device registration failed?
 		 * -- dtor
 		 */
 		device->cooling_dev = NULL;
@@ -1736,18 +1734,22 @@ static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 			&device->dev->dev.kobj, "device");
 	if (result)
 		printk(KERN_ERR PREFIX "Create sysfs link\n");
-	}
 }
 
 static int acpi_video_bus_register_backlight(struct acpi_video_bus *video)
 {
 	struct acpi_video_device *dev;
 
+	if (!acpi_video_verify_backlight_support())
+		return 0;
+
 	mutex_lock(&video->device_list_lock);
 	list_for_each_entry(dev, &video->video_device_list, entry)
 		acpi_video_dev_register_backlight(dev);
 	mutex_unlock(&video->device_list_lock);
 
+	video->backlight_registered = true;
+
 	video->pm_nb.notifier_call = acpi_video_resume;
 	video->pm_nb.priority = 0;
 	return register_pm_notifier(&video->pm_nb);
@@ -1775,13 +1777,20 @@ static void acpi_video_dev_unregister_backlight(struct acpi_video_device *device
 static int acpi_video_bus_unregister_backlight(struct acpi_video_bus *video)
 {
 	struct acpi_video_device *dev;
-	int error = unregister_pm_notifier(&video->pm_nb);
+	int error;
+
+	if (!video->backlight_registered)
+		return 0;
+
+	error = unregister_pm_notifier(&video->pm_nb);
 
 	mutex_lock(&video->device_list_lock);
 	list_for_each_entry(dev, &video->video_device_list, entry)
 		acpi_video_dev_unregister_backlight(dev);
 	mutex_unlock(&video->device_list_lock);
 
+	video->backlight_registered = false;
+
 	return error;
 }