VIO9P_SEGSIZE
VIO9P_N_SEGMENTS, VIO9P_SEGSIZE, 0, BUS_DMA_WAITOK, &sc->sc_dmamap_tx);
VIO9P_N_SEGMENTS, VIO9P_SEGSIZE, 0, BUS_DMA_WAITOK, &sc->sc_dmamap_rx);
#define VIO9P_N_SEGMENTS (VIO9P_MAX_REQLEN / VIO9P_SEGSIZE)