powerpc: Don't try OPAL takeover on old 970 blades

The firmware on old 970 blades supports some kind of takeover called
"TNK takeover" which will crash if we try to probe for OPAL takeover,
so don't do it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/prom_init.c

@@ -1313,6 +1313,16 @@ static void prom_query_opal(void)
 {
 	long rc;
 
+	/* We must not query for OPAL presence on a machine that
+	 * supports TNK takeover (970 blades), as this uses the same
+	 * h-call with different arguments and will crash
+	 */
+	if (PHANDLE_VALID(call_prom("finddevice", 1, 1,
+				    ADDR("/tnk-memory-map")))) {
+		prom_printf("TNK takeover detected, skipping OPAL check\n");
+		return;
+	}
+
 	prom_printf("Querying for OPAL presence... ");
 	rc = opal_query_takeover(&RELOC(prom_opal_size),
 				 &RELOC(prom_opal_align));