mmLB_VBLANK_STATUS
tmp = RREG32(mmLB_VBLANK_STATUS + crtc_offsets[crtc]);
WREG32(mmLB_VBLANK_STATUS + crtc_offsets[crtc], tmp);
WREG32(mmLB_VBLANK_STATUS + crtc_offsets[crtc], LB_VBLANK_STATUS__VBLANK_ACK_MASK);