[PATCH v5 3/9] of/overlay: look up absolute target-paths absolutely

[Abdurrahman Hussain]

find_target() with a non-NULL target base concatenates the base path
and the fragment's target-path via "%pOF%s": target-path="/foo"
resolves to "<base>/foo" and can never reach the DT root. An overlay
applied with a base cannot both extend the base subtree and add
/aliases entries, which is what a PCI device declaring its
peripherals under dev_of_node() needs for alias-based bus numbering.

Treat any non-empty target-path as absolute. An empty target-path
still means the base itself, the only form used by the one in-tree
caller passing a base (drivers/misc/lan966x_pci.c).

Spell the contract out in the kernel-doc for @base/@target_base and
in find_target()'s strategy comment.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
---
 drivers/of/overlay.c | 38 ++++++++++++++++++--------------------
 1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 08d5351746be..74aea704835a 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -688,12 +688,15 @@ static int build_changeset(struct overlay_changeset *ovcs)
  *
  * 1) "target" property containing the phandle of the target
  * 2) "target-path" property containing the path of the target
+ *
+ * With a non-NULL @target_base, an empty "target-path" means
+ * @target_base itself; any non-empty "target-path" is resolved
+ * absolutely from the live-tree root.
  */
 static struct device_node *find_target(const struct device_node *info_node,
 				       const struct device_node *target_base)
 {
 	struct device_node *node;
-	char *target_path;
 	const char *path;
 	u32 val;
 	int ret;
@@ -709,23 +712,14 @@ static struct device_node *find_target(const struct device_node *info_node,
 
 	ret = of_property_read_string(info_node, "target-path", &path);
 	if (!ret) {
-		if (target_base) {
-			target_path = kasprintf(GFP_KERNEL, "%pOF%s", target_base, path);
-			if (!target_path)
-				return NULL;
-			node = of_find_node_by_path(target_path);
-			if (!node) {
-				pr_err("find target, node: %pOF, path '%s' not found\n",
-				       info_node, target_path);
-			}
-			kfree(target_path);
-		} else {
-			node =  of_find_node_by_path(path);
-			if (!node) {
-				pr_err("find target, node: %pOF, path '%s' not found\n",
-				       info_node, path);
-			}
-		}
+		/* an empty target-path means the target base itself */
+		if (target_base && path[0] == '\0')
+			return of_node_get((struct device_node *)target_base);
+
+		node = of_find_node_by_path(path);
+		if (!node)
+			pr_err("find target, node: %pOF, path '%s' not found\n",
+			       info_node, path);
 		return node;
 	}
 
@@ -737,7 +731,9 @@ static struct device_node *find_target(const struct device_node *info_node,
 /**
  * init_overlay_changeset() - initialize overlay changeset from overlay tree
  * @ovcs:		Overlay changeset to build
- * @target_base:	Point to the target node to apply overlay
+ * @target_base:	Target for fragments with an empty "target-path";
+ *			fragments with a non-empty "target-path" resolve
+ *			absolutely and ignore @target_base
  *
  * Initialize @ovcs.  Populate @ovcs->fragments with node information from
  * the top level of @overlay_root.  The relevant top level nodes are the
@@ -982,7 +978,9 @@ static int of_overlay_apply(struct overlay_changeset *ovcs,
  * @overlay_fdt:	pointer to overlay FDT
  * @overlay_fdt_size:	number of bytes in @overlay_fdt
  * @ret_ovcs_id:	pointer for returning created changeset id
- * @base:		pointer for the target node to apply overlay
+ * @base:		target for fragments with an empty "target-path";
+ *			fragments with a non-empty "target-path" resolve
+ *			absolutely and ignore @base
  *
  * Creates and applies an overlay changeset.
  *

-- 
2.54.0