dm: core: Add ofnode functions to obtain an oftree

At present dm_test_ofnode_root() does this manually. Add some inline
functions to handle it, so this code can be centralised.

Add oftree functions to produce a null tree and to check whether a tree
is valid or not.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/dm/ofnode.h

@@ -173,6 +173,38 @@ static inline bool ofnode_equal(ofnode ref1, ofnode ref2)
 	return ref1.of_offset == ref2.of_offset;
 }
 
+/**
+ * oftree_valid() - check if an oftree is valid
+ *
+ * @tree: Reference containing oftree
+ * Return: true if the reference contains a valid oftree, false if node
+ */
+static inline bool oftree_valid(oftree tree)
+{
+	if (of_live_active())
+		return tree.np;
+	else
+		return tree.fdt;
+}
+
+/**
+ * oftree_null() - Obtain a null oftree
+ *
+ * This returns an oftree which points to no tree. It works both with the flat
+ * tree and livetree.
+ */
+static inline oftree oftree_null(void)
+{
+	oftree tree;
+
+	if (of_live_active())
+		tree.np = NULL;
+	else
+		tree.fdt = NULL;
+
+	return tree;
+}
+
 /**
  * ofnode_null() - Obtain a null ofnode
  *
@@ -234,6 +266,37 @@ static inline oftree oftree_default(void)
 	return tree;
 }
 
+/**
+ * oftree_from_np() - Returns an oftree from a node pointer
+ *
+ * @root: Root node of the tree
+ * Returns: reference to the given node
+ */
+static inline oftree oftree_from_np(struct device_node *root)
+{
+	oftree tree;
+
+	tree.np = root;
+
+	return tree;
+}
+
+/**
+ * oftree_from_fdt() - Returns an oftree from a flat device tree pointer
+ *
+ * @fdt: Device tree to use
+ *
+ * Returns: reference to the given node
+ */
+static inline oftree oftree_from_fdt(void *fdt)
+{
+	oftree tree;
+
+	tree.fdt = fdt;
+
+	return tree;
+}
+
 /**
  * ofnode_name_eq() - Check if the node name is equivalent to a given name
  *                    ignoring the unit address

test/dm/ofnode.c

@@ -518,13 +518,16 @@ static int dm_test_ofnode_root(struct unit_test_state *uts)
 	ut_assert(ofnode_valid(node));
 	ut_asserteq_str("sbe5", ofnode_get_name(node));
 
+	ut_assert(!oftree_valid(oftree_null()));
+
 	ut_assertok(make_ofnode_fdt(uts, fdt, sizeof(fdt)));
 	if (of_live_active()) {
 		ut_assertok(unflatten_device_tree(fdt, &root));
-		tree.np = root;
+		tree = oftree_from_np(root);
 	} else {
-		tree.fdt = fdt;
+		tree = oftree_from_fdt(fdt);
 	}
+	ut_assert(oftree_valid(tree));
 
 	/* Make sure they don't work on this new tree */
 	node = ofnode_path_root(tree, "mmc0");