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, 1 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index dcc6f159fd94..35ce07b6a5bc 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -107,12 +107,10 @@ int die(const char *str, struct pt_regs *regs, long err)
         if (machine_is(powermac) && pmac_backlight) {
                 struct backlight_properties *props;
 
-                down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
                 props->brightness = props->max_brightness;
                 props->power = FB_BLANK_UNBLANK;
-                props->update_status(pmac_backlight);
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
         }
         mutex_unlock(&pmac_backlight_mutex);
 #endif