drm_wait_vblank
#define DRM_IOCTL_WAIT_VBLANK DRM_IOWR(0x3a, union drm_wait_vblank)
typedef union drm_wait_vblank drm_wait_vblank_t;
extern int drm_wait_vblank(struct drm_device *dev, void *data,
DRM_IOCTL_DEF(DRM_IOCTL_WAIT_VBLANK, drm_wait_vblank, DRM_UNLOCKED),
union drm_wait_vblank request;
err = drm_wait_vblank(dev, (void *)&request, file_priv);
union drm_wait_vblank *vblwait,
union drm_wait_vblank *vblwait = data;