WDS_NSEG
sc->sc_maxsegs = WDS_NSEG;
#define WDS_MAXXFER ((WDS_NSEG - 1) << PGSHIFT)
error = bus_dmamap_create(dmat, WDS_MAXXFER, WDS_NSEG, WDS_MAXXFER,
struct wds_scat_gath scat_gath[WDS_NSEG];