VID_C_DMA_CTL
bus_space_write_4(sc->sc_memt, sc->sc_memh, VID_C_DMA_CTL, 0);
bus_space_write_4(sc->sc_memt, sc->sc_memh, VID_C_DMA_CTL, 0);
bus_space_write_4(sc->sc_memt, sc->sc_memh, VID_C_DMA_CTL, 0);
v = bus_space_read_4(sc->sc_memt, sc->sc_memh, VID_C_DMA_CTL);
bus_space_write_4(sc->sc_memt, sc->sc_memh, VID_C_DMA_CTL, v);