RADEON_DISP_MERGE_CNTL
disp_merge_cntl = RREG32(RADEON_DISP_MERGE_CNTL);
WREG32(RADEON_DISP_MERGE_CNTL, disp_merge_cntl);
disp_merge_cntl = RREG32(RADEON_DISP_MERGE_CNTL);
WREG32(RADEON_DISP_MERGE_CNTL, disp_merge_cntl);