1 files changed, 39 insertions, 11 deletions

diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index a5cf1beacb44..1023ba0d6e55 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -9,17 +9,28 @@
 #define _LINUX_BACKLIGHT_H
 
 #include <linux/device.h>
+#include <linux/mutex.h>
 #include <linux/notifier.h>
 
+/* Notes on locking:
+ *
+ * backlight_device->ops_lock is an internal backlight lock protecting the
+ * ops pointer and no code outside the core should need to touch it.
+ *
+ * Access to update_status() is serialised by the update_lock mutex since
+ * most drivers seem to need this and historically get it wrong.
+ *
+ * Most drivers don't need locking on their get_brightness() method.
+ * If yours does, you need to implement it in the driver. You can use the
+ * update_lock mutex if appropriate.
+ *
+ * Any other use of the locks below is probably wrong.
+ */
+
 struct backlight_device;
 struct fb_info;
 
-/* This structure defines all the properties of a backlight
-   (usually attached to a LCD). */
-struct backlight_properties {
-        /* Owner module */
-        struct module *owner;
-
+struct backlight_ops {
         /* Notify the backlight driver some property has changed */
         int (*update_status)(struct backlight_device *);
         /* Return the current backlight brightness (accounting for power,
@@ -28,7 +39,10 @@ struct backlight_properties {
         /* Check if given framebuffer device is the one bound to this backlight;
            return 0 if not, !=0 if it is. If NULL, backlight always matches the fb. */
         int (*check_fb)(struct fb_info *);
+};
 
+/* This structure defines all the properties of a backlight */
+struct backlight_properties {
         /* Current User requested brightness (0 - max_brightness) */
         int brightness;
         /* Maximal value for brightness (read-only) */
@@ -41,20 +55,34 @@ struct backlight_properties {
 };
 
 struct backlight_device {
-        /* This protects the 'props' field. If 'props' is NULL, the driver that
+        /* Backlight properties */
+        struct backlight_properties props;
+
+        /* Serialise access to update_status method */
+        struct mutex update_lock;
+
+        /* This protects the 'ops' field. If 'ops' is NULL, the driver that
            registered this device has been unloaded, and if class_get_devdata()
            points to something in the body of that driver, it is also invalid. */
-        struct semaphore sem;
-        /* If this is NULL, the backing module is unloaded */
-        struct backlight_properties *props;
+        struct mutex ops_lock;
+        struct backlight_ops *ops;
+
         /* The framebuffer notifier block */
         struct notifier_block fb_notif;
         /* The class device structure */
         struct class_device class_dev;
 };
 
+static inline void backlight_update_status(struct backlight_device *bd)
+{
+        mutex_lock(&bd->update_lock);
+        if (bd->ops && bd->ops->update_status)
+                bd->ops->update_status(bd);
+        mutex_unlock(&bd->update_lock);
+}
+
 extern struct backlight_device *backlight_device_register(const char *name,
-        struct device *dev,void *devdata,struct backlight_properties *bp);
+        struct device *dev, void *devdata, struct backlight_ops *ops);
 extern void backlight_device_unregister(struct backlight_device *bd);
 
 #define to_backlight_device(obj) container_of(obj, struct backlight_device, class_dev)