drm_vblank_count
.get_vblank_counter = drm_vblank_count,
extern u32 drm_vblank_count(struct drm_device *dev, int crtc);
seq = drm_vblank_count(dev, crtc);
while (((drm_vblank_count(dev, crtc) - vblwait->request.sequence) >
EXPORT_SYMBOL(drm_vblank_count);