amr_mailbox64
sc->amr_mailbox64->sg64_hi = ac->ac_sg64_hi;
sc->amr_mailbox64->sg64_lo = ac->ac_sg64_lo;
p = (void *)(uintptr_t)(volatile void *)sc->amr_mailbox64;
sizeof(struct amr_mailbox64), /* maxsize */
sizeof(struct amr_mailbox64), amr_sglist_helper, &baddr, 0);
sc->amr_mailboxphys = baddr + offsetof(struct amr_mailbox64, mb);
bzero(p, sizeof(struct amr_mailbox64));
sc->amr_mailbox64 = (struct amr_mailbox64 *)p;
sc->amr_mailbox = &sc->amr_mailbox64->mb;
volatile struct amr_mailbox64 *amr_mailbox64;