backlight: Add backlight_device_get_by_name()

Add a way to lookup a backlight device based on its name.
Will be used by a USB display gadget getting the name from configfs.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/video/backlight/backlight.c

@@ -432,6 +432,27 @@ struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
 }
 EXPORT_SYMBOL(backlight_device_get_by_type);
 
+/**
+ * backlight_device_get_by_name - Get backlight device by name
+ * @name: Device name
+ *
+ * This function looks up a backlight device by its name. It obtains a reference
+ * on the backlight device and it is the caller's responsibility to drop the
+ * reference by calling backlight_put().
+ *
+ * Returns:
+ * A pointer to the backlight device if found, otherwise NULL.
+ */
+struct backlight_device *backlight_device_get_by_name(const char *name)
+{
+	struct device *dev;
+
+	dev = class_find_device_by_name(backlight_class, name);
+
+	return dev ? to_backlight_device(dev) : NULL;
+}
+EXPORT_SYMBOL(backlight_device_get_by_name);
+
 /**
  * backlight_device_unregister - unregisters a backlight device object.
  * @bd: the backlight device object to be unregistered and freed.

include/linux/backlight.h

@@ -190,6 +190,7 @@ extern void backlight_force_update(struct backlight_device *bd,
 extern int backlight_register_notifier(struct notifier_block *nb);
 extern int backlight_unregister_notifier(struct notifier_block *nb);
 extern struct backlight_device *backlight_device_get_by_type(enum backlight_type type);
+struct backlight_device *backlight_device_get_by_name(const char *name);
 extern int backlight_device_set_brightness(struct backlight_device *bd, unsigned long brightness);
 
 #define to_backlight_device(obj) container_of(obj, struct backlight_device, dev)