libfdt: overlay: Fix phandle overwrite check for new subtrees

If the overlay's target is only created in a previous fragment, it
doesn't exist in the unmodified base device tree. For the phandle
overwrite check this can be ignored because in this case the base tree
doesn't contain a phandle that could be overwritten.

Adapt the corresponding check to not error out if that happens but just
continue with the next fragment.

This is currently triggered by
arch/arm64/boot/dts/renesas/salvator-panel-aa104xd12.dtso in the kernel
repository which creates /panel in its first fragment and modifies it in
its second.

Reported-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/all/CAL_JsqL9MPycDjqQfPNAuGfC6EMrdzUivr+fuOS7YgU3biGd4A@mail.gmail.com/
Fixes: 1fad065080 ("libfdt: overlay: ensure that existing phandles are not overwritten")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Message-ID: <20240626075551.2493048-2-u.kleine-koenig@baylibre.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_overlay.c

@@ -729,7 +729,13 @@ static int overlay_prevent_phandle_overwrite(void *fdt, void *fdto)
 			return overlay;
 
 		target = fdt_overlay_target_offset(fdt, fdto, fragment, NULL);
-		if (target < 0)
+		if (target == -FDT_ERR_NOTFOUND)
+			/*
+			 * The subtree doesn't exist in the base, so nothing
+			 * will be overwritten.
+			 */
+			continue;
+		else if (target < 0)
 			return target;
 
 		ret = overlay_prevent_phandle_overwrite_node(fdt, target,

tests/overlay_overlay_bypath.dts

@@ -46,3 +46,7 @@
 		new-sub-test-property;
 	};
 };
+
+&{/new-local-node} {
+	another-new-property;
+};

tests/overlay_overlay_no_fixups.dts

@@ -72,6 +72,14 @@
 		};
 	};
 
+	fragment@7 {
+		target-path = "/new-local-node";
+
+		__overlay__ {
+			another-new-property;
+		};
+	};
+
 	__local_fixups__ {
 		fragment@5 {
 			__overlay__ {