mmLB_VLINE_STATUS
tmp = RREG32(mmLB_VLINE_STATUS + crtc_offsets[crtc]);
WREG32(mmLB_VLINE_STATUS + crtc_offsets[crtc], tmp);
WREG32(mmLB_VLINE_STATUS + crtc_offsets[crtc], LB_VLINE_STATUS__VLINE_ACK_MASK);