RADEON_CRTC_V_DISP_SHIFT
if( v_display > V_2PIX(RADEON_CRTC_V_DISP >> RADEON_CRTC_V_DISP_SHIFT) - 5)
v_display = V_2PIX(RADEON_CRTC_V_DISP >> RADEON_CRTC_V_DISP_SHIFT) - 5;
| (((mode->timing.v_display - 1) << RADEON_CRTC_V_DISP_SHIFT) & RADEON_CRTC_V_DISP);
b = (r & RADEON_CRTC_V_DISP) >> RADEON_CRTC_V_DISP_SHIFT;