IER_ETXRDY
ns8250->ier |= IER_ETXRDY;
ns8250->ier &= ~IER_ETXRDY;
else if (sc->thre_int_pending && (sc->ier & IER_ETXRDY) != 0)
if ((sc->ier & IER_ETXRDY) == 0 && (value & IER_ETXRDY) != 0)