RADEON_CRTC_V_TOTAL_DISP
(RREG32(RADEON_CRTC_V_TOTAL_DISP) >> 16) + 1;
vbl = (RREG32(RADEON_CRTC_V_TOTAL_DISP) &
WREG32(RADEON_CRTC_V_TOTAL_DISP + radeon_crtc->crtc_offset, crtc_v_total_disp);