of: overlay: Extend of_overlay_fdt_apply() to specify the target node

Currently, in an overlay fdt fragment, it needs to specify the exact
location in base DT. In another word, when the fdt fragment is generated,
the base DT location for the fragment is already known.

There is new use case that the base DT location is unknown when fdt
fragment is generated. For example, the add-on device provide a fdt
overlay with its firmware to describe its downstream devices. Because it
is add-on device which can be plugged to different systems, its firmware
will not be able to know the overlay location in base DT. Instead, the
device driver will load the overlay fdt and apply it to base DT at runtime.
In this case, of_overlay_fdt_apply() needs to be extended to specify
the target node for device driver to apply overlay fdt.
int overlay_fdt_apply(..., struct device_node *base);

Signed-off-by: Lizhi Hou <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

drivers/of/overlay.c

···
  * 1) "target" property containing the phandle of the target
  * 2) "target-path" property containing the path of the target
  */
-static struct device_node *find_target(struct device_node *info_node)
+static struct device_node *find_target(struct device_node *info_node,
+				       struct device_node *target_base)
 {
 	struct device_node *node;
+	char *target_path;
 	const char *path;
 	u32 val;
 	int ret;
···
 
 	ret = of_property_read_string(info_node, "target-path", &path);
 	if (!ret) {
-		node =  of_find_node_by_path(path);
-		if (!node)
-			pr_err("find target, node: %pOF, path '%s' not found\n",
-			       info_node, path);
+		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);
+			}
+		}
 		return 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
  *
  * Initialize @ovcs.  Populate @ovcs->fragments with node information from
  * the top level of @overlay_root.  The relevant top level nodes are the
···
  * detected in @overlay_root.  On error return, the caller of
  * init_overlay_changeset() must call free_overlay_changeset().
  */
-static int init_overlay_changeset(struct overlay_changeset *ovcs)
+static int init_overlay_changeset(struct overlay_changeset *ovcs,
+				  struct device_node *target_base)
 {
 	struct device_node *node, *overlay_node;
 	struct fragment *fragment;
···
 
 		fragment = &fragments[cnt];
 		fragment->overlay = overlay_node;
-		fragment->target = find_target(node);
+		fragment->target = find_target(node, target_base);
 		if (!fragment->target) {
 			of_node_put(fragment->overlay);
 			ret = -EINVAL;
···
  *
  * of_overlay_apply() - Create and apply an overlay changeset
  * @ovcs:	overlay changeset
+ * @base:	point to the target node to apply overlay
  *
  * Creates and applies an overlay changeset.
  *
···
  * the caller of of_overlay_apply() must call free_overlay_changeset().
  */
 
-static int of_overlay_apply(struct overlay_changeset *ovcs)
+static int of_overlay_apply(struct overlay_changeset *ovcs,
+			    struct device_node *base)
 {
 	int ret = 0, ret_revert, ret_tmp;
 
···
 	if (ret)
 		goto out;
 
-	ret = init_overlay_changeset(ovcs);
+	ret = init_overlay_changeset(ovcs, base);
 	if (ret)
 		goto out;
 
···
  * @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
  *
  * Creates and applies an overlay changeset.
  *
···
  */
 
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
-			 int *ret_ovcs_id)
+			 int *ret_ovcs_id, struct device_node *base)
 {
 	void *new_fdt;
 	void *new_fdt_align;
···
 	}
 	ovcs->overlay_mem = overlay_mem;
 
-	ret = of_overlay_apply(ovcs);
+	ret = of_overlay_apply(ovcs, base);
 	/*
 	 * If of_overlay_apply() error, calling free_overlay_changeset() may
 	 * result in a memory leak if the apply partly succeeded, so do NOT

drivers/of/unittest.c

···
 	if (!size)
 		pr_err("no overlay data for %s\n", overlay_name);
 
-	ret = of_overlay_fdt_apply(info->dtbo_begin, size, &info->ovcs_id);
+	ret = of_overlay_fdt_apply(info->dtbo_begin, size, &info->ovcs_id,
+				   NULL);
 	if (ovcs_id)
 		*ovcs_id = info->ovcs_id;
 	if (ret < 0)

include/linux/of.h

···
 #ifdef CONFIG_OF_OVERLAY
 
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
-			 int *ovcs_id);
+			 int *ovcs_id, struct device_node *target_base);
 int of_overlay_remove(int *ovcs_id);
 int of_overlay_remove_all(void);