xen/device-tree: Add dt_find_node_by_path_from() to find nodes in device tree

Add dt_find_node_by_path_from() to find a matching node with path for a
dt_device_node.

Reason behind this function:
    Each time overlay nodes are added using .dtbo, a new fdt (memcpy of
    device_tree_flattened) is created and updated with overlay nodes. This
    updated fdt is further unflattened to a dt_host_new. Next, we need to find
    the overlay nodes in dt_host_new, find the overlay node's parent in dt_host
    and add the nodes as child under their parent in the dt_host. Thus we need
    this function to search for node in different unflattened device trees.

Also, make dt_find_node_by_path() static inline.

Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/common/device_tree.c

@@ -358,11 +358,12 @@ struct dt_device_node *dt_find_node_by_type(struct dt_device_node *from,
     return np;
 }
 
-struct dt_device_node *dt_find_node_by_path(const char *path)
+struct dt_device_node *dt_find_node_by_path_from(struct dt_device_node *from,
+                                                 const char *path)
 {
     struct dt_device_node *np;
 
-    dt_for_each_device_node(dt_host, np)
+    dt_for_each_device_node(from, np)
         if ( np->full_name && (dt_node_cmp(np->full_name, path) == 0) )
             break;
 

xen/include/xen/device_tree.h

@@ -570,13 +570,26 @@ struct dt_device_node *dt_find_node_by_type(struct dt_device_node *from,
 struct dt_device_node *dt_find_node_by_alias(const char *alias);
 
 /**
- * dt_find_node_by_path - Find a node matching a full DT path
+ * dt_find_node_by_path_from - Generic function to find a node matching the
+ * full DT path for any given unflatten device tree
+ * @from: The device tree node to start searching from
  * @path: The full path to match
  *
  * Returns a node pointer.
  */
-struct dt_device_node *dt_find_node_by_path(const char *path);
+struct dt_device_node *dt_find_node_by_path_from(struct dt_device_node *from,
+                                                 const char *path);
 
+/**
+ * dt_find_node_by_path - Find a node matching a full DT path in dt_host
+ * @path: The full path to match
+ *
+ * Returns a node pointer.
+ */
+static inline struct dt_device_node *dt_find_node_by_path(const char *path)
+{
+    return dt_find_node_by_path_from(dt_host, path);
+}
 
 /**
  * dt_find_node_by_gpath - Same as dt_find_node_by_path but retrieve the