DP_MIX
regw(sc, DP_MIX, (MIX_SRC << 16) | MIX_DST);
regw(sc, DP_MIX, ((MIX_SRC & 0xffff) << 16) | MIX_SRC);
regw(sc, DP_MIX, (rop & 0xffff) << 16);
regw(sc, DP_MIX, ((MIX_SRC & 0xffff) << 16) | MIX_SRC);
regw(sc, DP_MIX, MIX_SRC << 16);