drm_crtc_next_vblank_start
if (drm_crtc_next_vblank_start(crtc, &v))
EXPORT_SYMBOL(drm_crtc_next_vblank_start);
int drm_crtc_next_vblank_start(struct drm_crtc *crtc, ktime_t *vblanktime);