SM502_GPIO_DATA0
reg = bus_space_read_4(sc->sc_memt, sc->sc_regh, SM502_GPIO_DATA0);
bus_space_write_4(sc->sc_memt, sc->sc_regh, SM502_GPIO_DATA0, reg);
reg = bus_space_read_4(sc->sc_memt, sc->sc_regh, SM502_GPIO_DATA0);
voyager_twiddle_bits(cookie, SM502_GPIO_DATA0, m_and, m_or)