backlight: Fix external uses of backlight internal semaphore

backlight_device->sem has a very specific use as documented in the
header file. The external users of this are using it for a different
reason, to serialise access to the update_status() method.

backlight users were supposed to implement their own internal
serialisation of update_status() if needed but everyone is doing
things differently and incorrectly. Therefore add a global mutex to
take care of serialisation for everyone, once and for all.

Locking for get_brightness remains optional since most users don't
need it.

Also update the lcd class in a similar way.

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

2 files changed, 5 insertions, 6 deletions

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 7a85be4d2b0a..347081daf7a4 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -37,8 +37,7 @@ static int fb_notifier_callback(struct notifier_block *self,
                 if (!bd->props->check_fb ||
                     bd->props->check_fb(evdata->info)) {
                         bd->props->fb_blank = *(int *)evdata->data;
-                        if (bd->props && bd->props->update_status)
-                                bd->props->update_status(bd);
+                        backlight_update_status(bd);
                 }
         up(&bd->sem);
         return 0;
@@ -97,8 +96,7 @@ static ssize_t backlight_store_power(struct class_device *cdev, const char *buf,
         if (bd->props) {
                 pr_debug("backlight: set power to %d\n", power);
                 bd->props->power = power;
-                if (bd->props->update_status)
-                        bd->props->update_status(bd);
+                backlight_update_status(bd);
                 rc = count;
         }
         up(&bd->sem);
@@ -140,8 +138,7 @@ static ssize_t backlight_store_brightness(struct class_device *cdev, const char
                         pr_debug("backlight: set brightness to %d\n",
                                  brightness);
                         bd->props->brightness = brightness;
-                        if (bd->props->update_status)
-                                bd->props->update_status(bd);
+                        backlight_update_status(bd);
                         rc = count;
                 }
         }
@@ -230,6 +227,7 @@ struct backlight_device *backlight_device_register(const char *name,
         if (!new_bd)
                 return ERR_PTR(-ENOMEM);
 
+        mutex_init(&new_bd->update_lock);
         init_MUTEX(&new_bd->sem);
         new_bd->props = bp;
         memset(&new_bd->class_dev, 0, sizeof(new_bd->class_dev));
diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
index 959024812abc..1e1e61a4b5da 100644
--- a/drivers/video/backlight/lcd.c
+++ b/drivers/video/backlight/lcd.c
@@ -198,6 +198,7 @@ struct lcd_device *lcd_device_register(const char *name, void *devdata,
                 return ERR_PTR(-ENOMEM);
 
         init_MUTEX(&new_ld->sem);
+        mutex_init(&new_ld->update_lock);
         new_ld->props = lp;
         memset(&new_ld->class_dev, 0, sizeof(new_ld->class_dev));
         new_ld->class_dev.class = &lcd_class;