twa_request_bus_scan
static int twa_request_bus_scan(device_t, const char *, const int *);
twa_match, twa_attach, NULL, NULL, twa_request_bus_scan, NULL, 0);
error = twa_request_bus_scan(self, NULL, NULL);
twa_request_bus_scan(sc->twa_dv, "twa", 0);