DMAC_STOP
error = mgb_dmac_control(sc, start, channel, DMAC_STOP);
case DMAC_STOP:
mgb_dmac_control(sc, MGB_DMAC_RX_START, 0, DMAC_STOP);
mgb_dmac_control(sc, MGB_DMAC_TX_START, 0, DMAC_STOP);