RXCFG_DRTH_SHIFT
min(val, (RXCFG_DRTH >> RXCFG_DRTH_SHIFT) * RXCFG_FIFO_UNIT);
rxcfg |= ((lp->rx_drain_threshold/RXCFG_FIFO_UNIT) << RXCFG_DRTH_SHIFT);