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>

1 files changed, 0 insertions, 6 deletions

diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
index 416cde5893af..cd2c5574cf93 100644
--- a/drivers/usb/misc/appledisplay.c
+++ b/drivers/usb/misc/appledisplay.c
@@ -189,11 +189,9 @@ static void appledisplay_work(struct work_struct *work)
                 container_of(work, struct appledisplay, work.work);
         int retval;
 
-        up(&pdata->bd->sem);
         retval = appledisplay_bl_get_brightness(pdata->bd);
         if (retval >= 0)
                 pdata->bd->props->brightness = retval;
-        down(&pdata->bd->sem);
 
         /* Poll again in about 125ms if there's still a button pressed */
         if (pdata->button_pressed)
@@ -288,9 +286,7 @@ static int appledisplay_probe(struct usb_interface *iface,
         }
 
         /* Try to get brightness */
-        up(&pdata->bd->sem);
         brightness = appledisplay_bl_get_brightness(pdata->bd);
-        down(&pdata->bd->sem);
 
         if (brightness < 0) {
                 retval = brightness;
@@ -299,9 +295,7 @@ static int appledisplay_probe(struct usb_interface *iface,
         }
 
         /* Set brightness in backlight device */
-        up(&pdata->bd->sem);
         pdata->bd->props->brightness = brightness;
-        down(&pdata->bd->sem);
 
         /* save our data pointer in the interface device */
         usb_set_intfdata(iface, pdata);