[PATCH 1/2] fdt: Allow stacked overlays phandle references

@@ -15,3 +15,4 @@ lex.yy.c
 /fdtput
 /patches
 /.pc
+/fdtoverlay

@@ -590,7 +590,7 @@ static int overlay_apply_node(void *fdt, int target,
  *
  * overlay_merge() merges an overlay into its base device tree.
  *
- * This is the final step in the device tree overlay application
+ * This is the next to last step in the device tree overlay application
  * process, when all the phandles have been adjusted and resolved and
  * you just have to merge overlay into the base device tree.
  *

@@ -630,6 +630,148 @@ static int overlay_merge(void *fdt, void *fdto)
 	return 0;
 }
 
+/**
+ * overlay_symbol_update - Update the symbols of base tree after a merge
+ * @fdt: Base Device Tree blob
+ * @fdto: Device tree overlay blob
+ *
+ * overlay_symbol_update() updates the symbols of the base tree with the
+ * symbols of the applied overlay
+ *
+ * This is the last step in the device tree overlay application
+ * process, allowing the reference of overlay symbols by subsequent
+ * overlay operations.
+ *
+ * returns:
+ *      0 on success
+ *      Negative error code on failure
+ */
+static int overlay_symbol_update(void *fdt, void *fdto)
+{
+	int root_sym, ov_sym, prop, path_len, fragment, target;
+	int len, frag_name_len, ret, rel_path_len;
+	const char *s;
+	const char *path;
+	const char *name;
+	const char *frag_name;
+	const char *rel_path;
+	char *buf = NULL;
+
+	root_sym = fdt_subnode_offset(fdt, 0, "__symbols__");
+	ov_sym = fdt_subnode_offset(fdto, 0, "__symbols__");
+
+	/* if neither exist we can't update symbols, but that's OK */
+	if (root_sym < 0 || ov_sym < 0)
+		return 0;
+
+	buf = malloc(FDT_PATH_MAX);
+	if (!buf)
+		return -FDT_ERR_NOSPACE;
+
+	/* iterate over each overlay symbol */
+	fdt_for_each_property_offset(prop, fdto, ov_sym) {
+
+		path = fdt_getprop_by_offset(fdto, prop, &name, &path_len);
+		if (!path) {
+			ret = path_len;
+			goto out;
+		}
+
+		/* skip autogenerated properties */
+		if (!strcmp(name, "name"))
+			continue;
+
+		/* format: /<fragment-name>/__overlay__/<relative-subnode-path> */
+
+		if (*path != '/') {
+			ret = -FDT_ERR_BADVALUE;
+			goto out;
+		}
+
+		/* get frag name first */
+		s = strchr(path + 1, '/');
+		if (!s) {
+			ret = -FDT_ERR_BADVALUE;
+			goto out;
+		}
+		frag_name = path + 1;
+		frag_name_len = s - path - 1;
+
+		/* verify format */
+		len = strlen("/__overlay__/");
+		if (strncmp(s, "/__overlay__/", len)) {
+			ret = -FDT_ERR_NOTFOUND;
+			goto out;
+		}
+
+		rel_path = s + len;
+		rel_path_len = strlen(rel_path);
+
+		/* find the fragment index in which the symbol lies */
+		fdt_for_each_subnode(fragment, fdto, 0) {
+
+			s = fdt_get_name(fdto, fragment, &len);
+			if (!s)
+				continue;
+
+			/* name must match */
+			if (len == frag_name_len && !memcmp(s, frag_name, len))
+				break;
+		}
+
+		/* not found? */
+		if (fragment < 0) {
+			ret = -FDT_ERR_NOTFOUND;
+			goto out;
+		}
+
+		/* an __overlay__ subnode must exist */
+		ret = fdt_subnode_offset(fdto, fragment, "__overlay__");
+		if (ret < 0)
+			goto out;
+
+		/* get the target of the fragment */
+		ret = overlay_get_target(fdt, fdto, fragment);
+		if (ret < 0)
+			goto out;
+		target = ret;
+
+		/* get the path of the target */
+		ret = fdt_get_path(fdt, target, buf, FDT_PATH_MAX);
+		if (ret < 0)
+			goto out;
+
+		len = strlen(buf);
+
+		/* if the target is root strip leading / */
+		if (len == 1 && buf[0] == '/')
+			len = 0;
+
+		/* make sure we have enough space */
+		if (len + 1 + rel_path_len + 1 > FDT_PATH_MAX) {
+			ret = -FDT_ERR_NOSPACE;
+			goto out;
+		}
+
+		/* create new symbol path in place */
+		buf[len] = '/';
+		memcpy(buf + len + 1, rel_path, rel_path_len);
+		buf[len + 1 + rel_path_len] = '\0';
+
+		ret = fdt_setprop_string(fdt, root_sym, name, buf);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = 0;
+
+out:
+	if (buf)
+		free(buf);
+
+	return ret;
+}
+
 int fdt_overlay_apply(void *fdt, void *fdto)
 {
 	uint32_t delta = fdt_get_max_phandle(fdt);

@@ -654,6 +796,10 @@ int fdt_overlay_apply(void *fdt, void *fdto)
 	if (ret)
 		goto err;
 
+	ret = overlay_symbol_update(fdt, fdto);
+	if (ret)
+		goto err;
+
 	/*
 	 * The overlay has been damaged, erase its magic.
 	 */