Fix vblank enable/disable callbacks

There were two problems with the existing callback code:  the vblank
enable callback happened multiple times per disable, making drivers more
complex than they had to be, and there was a race between the final
decrement of the vblank usage counter and the next enable call, which
could have resulted in a put->schedule disable->get->enable->disable
sequence, which would be bad.

So add a new vblank_enabled array to track vblank enable on per-pipe
basis, and add a lock to protect it along with the refcount +
enable/disable calls to fix the race.

1 files changed, 2 insertions, 0 deletions

diff --git a/linux-core/drmP.h b/linux-core/drmP.h
index 4e8b087b..33f3649e 100644
--- a/linux-core/drmP.h
+++ b/linux-core/drmP.h
@@ -836,6 +836,8 @@ struct drm_device {
 	u32 *last_vblank;		/* protected by dev->vbl_lock, used */
 					/* for wraparound handling */
 	u32 *vblank_offset;		/* used to track how many vblanks */
+	int *vblank_enabled;		/* so we don't call enable more than
+					   once per disable */
 	u32 *vblank_premodeset;		/*  were lost during modeset */
 	struct timer_list vblank_disable_timer;