GUS_DMAIN_ACTIVE
KASSERT((sc->sc_flags & GUS_DMAIN_ACTIVE) == 0);
if (sc->sc_flags & GUS_DMAIN_ACTIVE) {
sc->sc_flags |= GUS_DMAIN_ACTIVE;
sc->sc_flags &= ~GUS_DMAIN_ACTIVE;
sc->sc_flags &= ~GUS_DMAIN_ACTIVE;