drm: Send pending vblank events before disabling vblank.

This is the least-bad behaviour.  It means that we signal the
vblank event before it actually happens, but since we're disabling
vblanks there's no guarantee that it will *ever* happen otherwise.

This prevents GL applications which use WaitMSC from hanging
indefinitely.

Signed-off-by: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_irq.c

@@ -932,11 +932,34 @@ EXPORT_SYMBOL(drm_vblank_put);
 
 void drm_vblank_off(struct drm_device *dev, int crtc)
 {
+	struct drm_pending_vblank_event *e, *t;
+	struct timeval now;
 	unsigned long irqflags;
+	unsigned int seq;
 
 	spin_lock_irqsave(&dev->vbl_lock, irqflags);
 	vblank_disable_and_save(dev, crtc);
 	DRM_WAKEUP(&dev->vbl_queue[crtc]);
+
+	/* Send any queued vblank events, lest the natives grow disquiet */
+	seq = drm_vblank_count_and_time(dev, crtc, &now);
+	list_for_each_entry_safe(e, t, &dev->vblank_event_list, base.link) {
+		if (e->pipe != crtc)
+			continue;
+		DRM_DEBUG("Sending premature vblank event on disable: \
+			  wanted %d, current %d\n",
+			  e->event.sequence, seq);
+
+		e->event.sequence = seq;
+		e->event.tv_sec = now.tv_sec;
+		e->event.tv_usec = now.tv_usec;
+		drm_vblank_put(dev, e->pipe);
+		list_move_tail(&e->base.link, &e->base.file_priv->event_list);
+		wake_up_interruptible(&e->base.file_priv->event_wait);
+		trace_drm_vblank_event_delivered(e->base.pid, e->pipe,
+						 e->event.sequence);
+	}
+
 	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
 }
 EXPORT_SYMBOL(drm_vblank_off);