MGB_DMAC_RX_START
mgb_dmac_control(sc, MGB_DMAC_RX_START, 0, DMAC_RESET);
KASSERT(MGB_DMAC_STATE_IS_INITIAL(sc, MGB_DMAC_RX_START, channel),
mgb_dmac_control(sc, MGB_DMAC_RX_START, channel, DMAC_START);
mgb_dmac_control(sc, MGB_DMAC_RX_START, 0, DMAC_STOP);