GPIO_IMR
bus_space_write_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR, 0);
mask = bus_space_read_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR);
bus_space_write_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR,
bus_space_read_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR) | 1 << irqno);
mask = bus_space_read_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR);
bus_space_write_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR, mask);
mask = bus_space_read_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR);
bus_space_write_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR, mask);
mask = bus_space_read_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR);
bus_space_write_4(sc->sc_iot, sc->sc_ioh, GPIO_IMR, mask);