of: detect invalid phandle in overlay

Overlays are not allowed to modify phandle values of previously existing
nodes because there is no information available to allow fixup up
properties that use the previously existing phandle.
Signed-off-by: NFrank Rowand <frank.rowand@sony.com>
Signed-off-by: NRob Herring <robh@kernel.org>

drivers/of/overlay.c

@@ -132,6 +132,10 @@ static int of_overlay_apply_single_device_node(struct of_overlay *ov,
 	/* NOTE: Multiple mods of created nodes not supported */
 	tchild = of_get_child_by_name(target, cname);
 	if (tchild != NULL) {
+		/* new overlay phandle value conflicts with existing value */
+		if (child->phandle)
+			return -EINVAL;
+
 		/* apply overlay recursively */
 		ret = of_overlay_apply_one(ov, tchild, child);
 		of_node_put(tchild);