backlight: Rework backlight/fb interaction simplifying, lots

fb_info->bl_mutex is badly thought out and the backlight class doesn't
need it if the framebuffer/backlight register/unregister order is
consistent, particularly after the backlight locking fixes.

Fix the drivers to use the order:

backlight_device_register()
register_framebuffer()
unregister_framebuffer()
backlight_device_unregister()

and turn bl_mutex into a lock for the bl_curve data only.

Signed-off-by: Richard Purdie <rpurdie@rpsys.net>

1 files changed, 3 insertions, 6 deletions

diff --git a/include/linux/fb.h b/include/linux/fb.h
index bf7158b59b25..be913ec87169 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -769,16 +769,13 @@ struct fb_info {
         struct fb_videomode *mode;      /* current mode */
 
 #ifdef CONFIG_FB_BACKLIGHT
-        /* Lock ordering:
-         * bl_mutex (protects bl_dev and bl_curve)
-         *   bl_dev->sem (backlight class)
-         */
-        struct mutex bl_mutex;
-
         /* assigned backlight device */
+        /* set before framebuffer registration, 
+           remove after unregister */
         struct backlight_device *bl_dev;
 
         /* Backlight level curve */
+        struct mutex bl_curve_mutex;    
         u8 bl_curve[FB_BACKLIGHT_LEVELS];
 #endif