CPSW_TXFRAGS
bus_dma_segment_t segs[CPSW_TXFRAGS];
if (i > CPSW_TXFRAGS)
cpsw_write_4(sc, CPSW_CPDMA_RX_PENDTHRESH(0), CPSW_TXFRAGS);
MCLBYTES, CPSW_TXFRAGS, /* maxsize, nsegments */