RADEON_CRTC_V_SYNC_STRT
if( v_sync_start > V_2PIX(RADEON_CRTC_V_SYNC_STRT) - 4)
v_sync_start = V_2PIX(RADEON_CRTC_V_SYNC_STRT) - 4;
((mode->timing.v_sync_start - 1) & RADEON_CRTC_V_SYNC_STRT)
di->fp_info.v_over_plus = (r & RADEON_CRTC_V_SYNC_STRT) - b;