Index: sys/powerpc/powermac/smu.c
===================================================================
--- sys/powerpc/powermac/smu.c
+++ sys/powerpc/powermac/smu.c
@@ -278,22 +278,14 @@
 	sc->sc_cmd_phys = segs[0].ds_addr;
 }
 
-static int
-smu_attach(device_t dev)
+static void
+smu_intrhook(void *xsc)
 {
-	struct smu_softc *sc;
+	struct smu_softc *sc = xsc;
 	phandle_t	node, child;
 	uint8_t		data[12];
 
-	sc = device_get_softc(dev);
-
-	mtx_init(&sc->sc_mtx, "smu", NULL, MTX_DEF);
-	sc->sc_cur_cmd = NULL;
-	sc->sc_doorbellirqid = -1;
-
-	sc->sc_u3 = 0;
-	if (OF_finddevice("/u3") != -1)
-		sc->sc_u3 = 1;
+	KASSERT(smu_doorbell != NULL, "SMC Dooorbell missing");
 
 	/*
 	 * Map the mailbox area. This should be determined from firmware,
@@ -405,6 +397,26 @@
 	return (bus_generic_attach(dev));
 }
 
+static int
+smu_attach(device_t dev)
+{
+	struct smu_softc *sc;
+
+	sc = device_get_softc(dev);
+
+	mtx_init(&sc->sc_mtx, "smu", NULL, MTX_DEF);
+	sc->sc_cur_cmd = NULL;
+	sc->sc_doorbellirqid = -1;
+
+	sc->sc_u3 = 0;
+	if (OF_finddevice("/u3") != -1)
+		sc->sc_u3 = 1;
+
+	/* Defer everything else until we have interrupts and the doorbell device */
+	config_intrhook_oneshot(smc_intrhook, sc);
+	return (0);
+}
+
 static const struct ofw_bus_devinfo *
 smu_get_devinfo(device_t bus, device_t dev)
 {