dvma_alloc
si->si_dmaaddr = dvma_alloc(dip->d_dmabytes);
extern char *dvma_alloc(int);
dd->rbuf = dvma_alloc(dd->rbuf_len);
dd->tbuf = dvma_alloc(dd->tbuf_len);
si->si_dmaaddr = dvma_alloc(dip->d_dmabytes);