[PATCH 4/7] of: resolver: Add support for the export symbols node

[Herve Codina <herve.codina@bootlin.com>]

Symbols resolution done when an overlay is applied looks only at the
global __symbol__ node to resolve unknown symbols from the overlay (i.e
symbols listed in the overlay __fixups__ node).

In order to provide flexibilities and allow to define some additional
symbols visible only when an overlay is applied to a specific node,
introduce the export symbols node.

The export symbols node adds some additional symbols that can be used
in the symbols resolution. The resolver tries to match unresolved
symbols first using the export symbols node and, if a match is not
found, it tries to match using the global __symbol__ node.

Contrary to symbols available in the global __symbols__ node, symbols
listed in the export symbols node can be considered as local symbols.
Indeed, they can be changed depending on the node the overlay is going
to be applied to and are only visibible from the current recolver call.

Handle those additional symbols given by the export symbols node in the
symbols resolution.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/of/resolver.c | 33 +++++++++++++++++++++++++++++----
 drivers/of/unittest.c |  4 ++--
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
index f5f6c46231d1..b685c46b20b8 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c
@@ -222,6 +222,9 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
 	const char *refpath;
 	int err;
 
+	if (!tree_symbols)
+		return -ENOENT;
+
 	err = of_property_read_string(tree_symbols, symbol_name, &refpath);
 	if (err)
 		return err;
@@ -236,6 +239,25 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
 	return 0;
 }
 
+static int get_phandle_from_export_node(const struct device_node *export_symbols,
+					const char *symbol_name,
+					phandle *phandle)
+{
+	struct device_node *refnode;
+
+	if (!export_symbols)
+		return -ENOENT;
+
+	refnode = of_parse_phandle(export_symbols, symbol_name, 0);
+	if (!refnode)
+		return -ENOENT;
+
+	*phandle = refnode->phandle;
+	of_node_put(refnode);
+
+	return 0;
+}
+
 /**
  * of_resolve_phandles - Relocate and resolve overlay against live tree
  *
@@ -320,7 +342,7 @@ int of_resolve_phandles(struct device_node *overlay, const struct device_node *e
 	}
 
 	tree_symbols = of_find_node_by_path("/__symbols__");
-	if (!tree_symbols) {
+	if (!tree_symbols && !export_symbols) {
 		pr_err("no symbols in root of device tree.\n");
 		err = -EINVAL;
 		goto out;
@@ -332,10 +354,13 @@ int of_resolve_phandles(struct device_node *overlay, const struct device_node *e
 		if (!of_prop_cmp(prop->name, "name"))
 			continue;
 
-		err = get_phandle_from_symbols_node(tree_symbols, prop->name,
-						    &phandle);
+		err = get_phandle_from_export_node(export_symbols, prop->name,
+						   &phandle);
+		if (err)
+			err = get_phandle_from_symbols_node(tree_symbols, prop->name,
+							    &phandle);
 		if (err) {
-			pr_err("node label '%s' not found or invalid in live devicetree symbols table\n",
+			pr_err("node label '%s' not found or invalid in live devicetree symbols or export tables\n",
 			       prop->name);
 			goto out;
 		}
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 7b97d4fc0236..e76ac087ea98 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -4025,7 +4025,7 @@ static __init void of_unittest_overlay_high_level(void)
 	/* ---  overlay_bad_unresolved  --- */
 
 	EXPECT_BEGIN(KERN_ERR,
-		     "OF: resolver: node label 'this_label_does_not_exist' not found in live devicetree symbols table");
+		     "OF: resolver: node label 'this_label_does_not_exist' not found or invalid in live devicetree symbols or export tables");
 	EXPECT_BEGIN(KERN_ERR,
 		     "OF: resolver: overlay phandle fixup failed: -22");
 
@@ -4035,7 +4035,7 @@ static __init void of_unittest_overlay_high_level(void)
 	EXPECT_END(KERN_ERR,
 		   "OF: resolver: overlay phandle fixup failed: -22");
 	EXPECT_END(KERN_ERR,
-		   "OF: resolver: node label 'this_label_does_not_exist' not found in live devicetree symbols table");
+		   "OF: resolver: node label 'this_label_does_not_exist' not found or invalid in live devicetree symbols or export tables");
 
 	return;
 
-- 
2.47.0