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

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

[Herve Codina]

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

[PATCH 0/7] of: overlay: Add support for export-symbols node feature

[Herve Codina]

Hi,

At Linux Plumbers Conference 2024, we (me and Luca Ceresolli) talked
about issues we have with runtime hotplug on non-discoverable busses
with device tree overlays [1].

On our system, a base board has a connector and addon boards can be
connected to this connector. Both boards are described using device
tree. The base board is described by a base device tree and addon boards
are describe by overlays device tree. More details can be found at [2].

This kind of use case can be found also on:
  - Grove Sunlight Sensor [3]
  - mikroBUS [4]

One of the issue we were facing on was referencing resources available
on the base board device tree from the addon overlay device tree.

Using a nexus node [5] helps decoupling resources and avoid the
knowledge of the full base board from the overlay. Indeed, with nexus
node, the overlay need to know only about the nexus node itself.

For instance, suppose a connector where a GPIO is connected at PinA. On
the base board this GPIO is connected to the GPIO 12 of the SoC GPIO
controller.

The base board can describe this GPIO using a nexus node:
    soc_gpio: gpio-controller {
      #gpio-cells = <2>;
    };

    connector1: connector1 {
        /*
         * Nexus node for the GPIO available on the connector.
         * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
         * controller
         */
        #gpio-cells = <2>;
        gpio-map = <0 0 &soc_gpio 12 0>;
        gpio-map-mask = <0xf 0x0>;
        gpio-map-pass-thru = <0x0 0xf>;
    };

The connector pin A GPIO can be referenced using:
  <&connector1 0 GPIO_ACTIVE_HIGH>

This implies that the overlay needs to know about exact label that
references the connector. This label can be different on a different
board and so applying the overlay could failed even if it is used to
describe the exact same addon board. Further more, a given base board
can have several connectors where the exact same addon board can be
connected. In that case, the same overlay cannot be used on both
connector. Indeed, the connector labels have to be different.

The export-symbols node introduced by this current series solves this
issue.

The idea of export-symbols is to have something similar to the global
__symbols__ node but local to a specific node. Symbols listed in this
export-symbols are local and visible only when an overlay is applied on
a node having an export-symbols subnode.

Using export-symbols, our example becomes:
    soc_gpio: gpio-controller {
      #gpio-cells = <2>;
    };

    connector1: connector1 {
        /*
         * Nexus node for the GPIO available on the connector.
         * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
         * controller
         */
        #gpio-cells = <2>;
        gpio-map = <0 0 &soc_gpio 12 0>;
        gpio-map-mask = <0xf 0x0>;
        gpio-map-pass-thru = <0x0 0xf>;

        export-symbols {
          connector = <&connector1>;
        };
    };

With that export-symbols node, an overlay applied on connector1 node can
have the symbol named 'connector' resolved to connector1. Indeed, the
export-symbols node available at connector1 node is used when the
overlay is applied. If the overlay has an unresolved 'connector' symbol,
it will be resolved to connector1 thanks to export-symbols.

Our overlay using the nexus node can contains:
   node {
      foo-gpio = <&connector 0 GPIO_ACTIVE_HIGH>;
   };
It used the GPIO 0 from the connector it is applied on.

A board with two connectors can be described with:
    connector1: connector1 {
        ...
        export-symbols {
          connector = <&connector1>;
        };
    };

    connector2: connector2 {
        ...
        export-symbols {
          connector = <&connector2>;
        };
    };

In that case, the same overlay with unresolved 'connector' symbol can be
applied on both connectors and the correct symbol resolution (connector1
or connector2) will be done.

This current series add support for the export-symbols node feature:
  - Patch 1 describes the export-symbols binding
  - Patches 2 to 6 prepare and add the support for the export-symbols
    feature
  - Patch 7 adds an unittest for the export-symbols feature

Compare to the previous iteration, the series has been rebased on
top of v6.15-rc1 and an compilation issue in unittest has been fixed.

Also it is worth noting the work already done by Ayush Singh related to
this topic on other repositories:
  - Add export-symbols in device-tree specification
      [PATCH v3] Add new `export-symbols` node [6]

  - Support for export-symbols in the device tree compiler
      [PATCH 0/3] Allow specifying target node in fdtoverlay [7]
      [PATCH] checks: Add support for export-symbols [8]

Best regards,
Hervé

[1] https://lpc.events/event/18/contributions/1696/
[2] https://lore.kernel.org/lkml/20240917-hotplug-drm-bridge-v4-0-bc4dfee61be6@bootlin.com/
[3] https://lore.kernel.org/lkml/20240702164403.29067-1-afd@ti.com/
[4] https://lore.kernel.org/lkml/20240627-mikrobus-scratch-spi-v5-0-9e6c148bf5f0@beagleboard.org/
[5] https://github.com/devicetree-org/devicetree-specification/blob/v0.4/source/chapter2-devicetree-basics.rst#nexus-nodes-and-specifier-mapping
[6] https://lore.kernel.org/all/20250411-export-symbols-v3-1-f59368d97063@beagleboard.org/
[7] https://lore.kernel.org/all/20250313-fdtoverlay-target-v1-0-dd5924e12bd3@beagleboard.org/
[8] https://lore.kernel.org/all/20250110-export-symbols-v1-1-b6213fcd6c82@beagleboard.org/

Changes v1 -> v2
  v1: https://lore.kernel.org/all/20241209151830.95723-1-herve.codina@bootlin.com/

  - All patches
    Add 'Tested-by: Ayush Singh <ayush@beagleboard.org>'

  - Patch 1
    Update the 'patternProperties' regexp

  - Patch 2 and 4
    Fix conflicts due to the rebase on top of v6.15-rc1

  - Patch 5
    Fix a typo in commit log

  - Patch 7
    Fix a compilation issue detected by a kernel test robot

Herve Codina (7):
  dt-bindings: Add support for export-symbols node
  of: resolver: Introduce get_phandle_from_symbols_node()
  of: resolver: Add export_symbols in of_resolve_phandles() parameters
  of: resolver: Add support for the export symbols node
  of: overlay: Add export_symbols_name in of_overlay_fdt_apply()
    parameters
  of: overlay: Add support for the export symbols node
  of: unittest: Add tests for export symbols

 .../devicetree/bindings/export-symbols.yaml   | 43 +++++++++++
 drivers/misc/lan966x_pci.c                    |  3 +-
 drivers/of/of_kunit_helpers.c                 |  2 +-
 drivers/of/of_private.h                       |  2 +-
 drivers/of/overlay.c                          | 30 +++++++-
 drivers/of/resolver.c                         | 75 ++++++++++++++----
 drivers/of/unittest-data/Makefile             |  5 ++
 .../unittest-data/overlay_export_symbols.dtso | 15 ++++
 .../of/unittest-data/testcases_common.dtsi    |  1 +
 .../unittest-data/tests-export-symbols.dtsi   | 30 ++++++++
 drivers/of/unittest.c                         | 77 +++++++++++++++++--
 include/linux/of.h                            |  6 +-
 12 files changed, 258 insertions(+), 31 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/export-symbols.yaml
 create mode 100644 drivers/of/unittest-data/overlay_export_symbols.dtso
 create mode 100644 drivers/of/unittest-data/tests-export-symbols.dtsi

-- 
2.49.0

[PATCH 1/7] dt-bindings: Add support for export-symbols node

[Herve Codina]

An export-symbols node allows to export symbols for symbols resolution
performed when applying a device tree overlay.

When a device tree overlay is applied on a node having an export-symbols
node, symbols listed in the export-symbols node are used to resolve
undefined symbols referenced from the overlay.

This allows:
  - Referencing symbols from an device tree overlay without the need to
    know the full base board. Only the connector definition is needed.

  - Using the exact same overlay on several connectors available on a given
    board.

For instance, the following description is supported with the
export-symbols node:
 - Base device tree board A:
    ...
    foo_connector: connector1 {
        export-symbols {
           connector = <&foo_connector>;
        };
    };

    bar_connector: connector2 {
        export-symbols {
           connector = <&bar_connector>;
        };
    };
    ...

 - Base device tree board B:
    ...
    front_connector: addon-connector {
        export-symbols {
           connector = <&front_connector>;
        };
    };
    ...

 - Overlay describing an addon board the can be connected on connectors:
    ...
    node {
        ...
        connector = <&connector>;
        ...
    };
    ...

Thanks to the export-symbols node, the overlay can be applied on
connector1 or connector2 available on board A but also on
addon-connector available on board B.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 .../devicetree/bindings/export-symbols.yaml   | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/export-symbols.yaml

diff --git a/Documentation/devicetree/bindings/export-symbols.yaml b/Documentation/devicetree/bindings/export-symbols.yaml
new file mode 100644
index 000000000000..0e404eff8937
--- /dev/null
+++ b/Documentation/devicetree/bindings/export-symbols.yaml
@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/export-symbols.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Export symbols
+
+maintainers:
+  - Herve Codina <herve.codina@bootlin.com>
+
+description: |
+  An export-symbols node allows to export symbols for symbols resolution
+  performed when applying a device tree overlay.
+
+  When a device tree overlay is applied on a node having an export-symbols
+  node, symbols listed in the export-symbols node are used to resolve undefined
+  symbols referenced from the overlay.
+
+properties:
+  $nodename:
+    const: export-symbols
+
+patternProperties:
+  "^[a-zA-Z_]?[a-zA-Z0-9_]*$":
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description:
+      A symbol exported in the form <symbol_name>=<phandle>.
+
+additionalProperties: false
+
+examples:
+  - |
+    /*
+     * Allows 'connector' symbol used in a device-tree overlay to be resolved to
+     * connector0 when the device-tree overlay is applied on connector0 node.
+     */
+    connector0: connector0 {
+      export-symbols {
+        connector = <&connector0>;
+      };
+    };
+...
-- 
2.49.0

[PATCH 2/7] of: resolver: Introduce get_phandle_from_symbols_node()

[Herve Codina]

In order to simplify the introduction of the export symbols node
handling, group necessary operations done to get a phandle from the
__symbols__ node in this dedicated get_phandle_from_symbols_node()
function.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 drivers/of/resolver.c | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
index 86424e145919..2c7a3b479b15 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c
@@ -212,6 +212,28 @@ static int adjust_local_phandle_references(const struct device_node *local_fixup
 	return 0;
 }
 
+static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
+					 const char *symbol_name,
+					 phandle *phandle)
+{
+	struct device_node *refnode;
+	const char *refpath;
+	int err;
+
+	err = of_property_read_string(tree_symbols, symbol_name, &refpath);
+	if (err)
+		return err;
+
+	refnode = of_find_node_by_path(refpath);
+	if (!refnode)
+		return -ENOENT;
+
+	*phandle = refnode->phandle;
+	of_node_put(refnode);
+
+	return 0;
+}
+
 /**
  * of_resolve_phandles - Relocate and resolve overlay against live tree
  *
@@ -247,11 +269,9 @@ static int adjust_local_phandle_references(const struct device_node *local_fixup
  */
 int of_resolve_phandles(struct device_node *overlay)
 {
-	struct device_node *child, *refnode;
-	struct device_node *overlay_fixups;
+	struct device_node *child, *overlay_fixups;
 	struct device_node __free(device_node) *local_fixups = NULL;
 	struct property *prop;
-	const char *refpath;
 	phandle phandle, phandle_delta;
 	int err;
 
@@ -298,21 +318,14 @@ int of_resolve_phandles(struct device_node *overlay)
 		if (!of_prop_cmp(prop->name, "name"))
 			continue;
 
-		err = of_property_read_string(tree_symbols,
-				prop->name, &refpath);
+		err = get_phandle_from_symbols_node(tree_symbols, prop->name,
+						    &phandle);
 		if (err) {
-			pr_err("node label '%s' not found in live devicetree symbols table\n",
+			pr_err("node label '%s' not found or invalid in live devicetree symbols table\n",
 			       prop->name);
 			return err;
 		}
 
-		refnode = of_find_node_by_path(refpath);
-		if (!refnode)
-			return -ENOENT;
-
-		phandle = refnode->phandle;
-		of_node_put(refnode);
-
 		err = update_usages_of_a_phandle_reference(overlay, prop, phandle);
 		if (err)
 			break;
-- 
2.49.0

[PATCH 3/7] of: resolver: Add export_symbols in of_resolve_phandles() parameters

[Herve Codina]

In order to prepare the introduction of the export symbols node
handling, add a export_symbols parameter in of_resolve_phandles().

The export_symbols is the export symbols device tree node the resolver
will use for the overlay symbols resolution.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 drivers/of/of_private.h | 2 +-
 drivers/of/overlay.c    | 2 +-
 drivers/of/resolver.c   | 9 +++++++--
 drivers/of/unittest.c   | 4 ++--
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index df0bb00349e0..cf68edb873ab 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -94,7 +94,7 @@ static inline void __of_detach_node_sysfs(struct device_node *np) {}
 #endif
 
 #if defined(CONFIG_OF_RESOLVE)
-int of_resolve_phandles(struct device_node *tree);
+int of_resolve_phandles(struct device_node *tree, const struct device_node *export_symbols);
 #endif
 
 void __of_phandle_cache_inv_entry(phandle handle);
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 1af6f52d0708..aa1b97e634aa 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -919,7 +919,7 @@ static int of_overlay_apply(struct overlay_changeset *ovcs,
 {
 	int ret = 0, ret_revert, ret_tmp;
 
-	ret = of_resolve_phandles(ovcs->overlay_root);
+	ret = of_resolve_phandles(ovcs->overlay_root, NULL);
 	if (ret)
 		goto out;
 
diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
index 2c7a3b479b15..5c492711b21f 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c
@@ -237,7 +237,8 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
 /**
  * of_resolve_phandles - Relocate and resolve overlay against live tree
  *
- * @overlay:	Pointer to devicetree overlay to relocate and resolve
+ * @overlay:		Pointer to devicetree overlay to relocate and resolve
+ * @export_symbols:	Pointer to devicetree export symbols node.
  *
  * Modify (relocate) values of local phandles in @overlay to a range that
  * does not conflict with the live expanded devicetree.  Update references
@@ -257,6 +258,10 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
  * corresponding to that symbol in the live tree.  Update the references in
  * the overlay with the phandle values in the live tree.
  *
+ * @export_symbols can be use in this references update. The resolver tries
+ * first to find a match in the @export_symbols. If not found, it uses the
+ * "__symbol__" node in the live tree.
+ *
  * @overlay must be detached.
  *
  * Resolving and applying @overlay to the live expanded devicetree must be
@@ -267,7 +272,7 @@ static int get_phandle_from_symbols_node(const struct device_node *tree_symbols,
  *
  * Return: %0 on success or a negative error value on error.
  */
-int of_resolve_phandles(struct device_node *overlay)
+int of_resolve_phandles(struct device_node *overlay, const struct device_node *export_symbols)
 {
 	struct device_node *child, *overlay_fixups;
 	struct device_node __free(device_node) *local_fixups = NULL;
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 64d301893af7..620237365566 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -2026,7 +2026,7 @@ static int __init unittest_data_add(void)
 	 */
 	of_overlay_mutex_lock();
 
-	rc = of_resolve_phandles(unittest_data_node);
+	rc = of_resolve_phandles(unittest_data_node, NULL);
 	if (rc) {
 		pr_err("%s: Failed to resolve phandles (rc=%i)\n", __func__, rc);
 		of_overlay_mutex_unlock();
@@ -3915,7 +3915,7 @@ static __init void of_unittest_overlay_high_level(void)
 	 * because kmalloc() was not yet available.
 	 */
 	of_overlay_mutex_lock();
-	of_resolve_phandles(overlay_base_root);
+	of_resolve_phandles(overlay_base_root, NULL);
 	of_overlay_mutex_unlock();
 
 
-- 
2.49.0

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

[Herve Codina]

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>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 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 5c492711b21f..c2b63cec1865 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c
@@ -220,6 +220,9 @@ 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;
@@ -234,6 +237,25 @@ 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
  *
@@ -312,7 +334,7 @@ int of_resolve_phandles(struct device_node *overlay, const struct device_node *e
 		return 0;
 
 	struct device_node __free(device_node) *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");
 		return -EINVAL;
 	}
@@ -323,10 +345,13 @@ 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);
 			return err;
 		}
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 620237365566..658690fd6980 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -4146,7 +4146,7 @@ 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");
 
@@ -4156,7 +4156,7 @@ 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;
 
-- 
2.49.0

[PATCH 5/7] of: overlay: Add export_symbols_name in of_overlay_fdt_apply() parameters

[Herve Codina]

In order to prepare the introduction of the export symbols node
handling, add a export_symbols_name parameter in of_overlay_fdt_apply().

The export_symbols_name is the name of the export symbols subnode
available in the base node that will be used by the resolver to handle
export symbols resolution.

Having the name of the subnode in parameters instead of the subnode
itself avoids the use of an export symbol node that is not directly
related to the base node.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 drivers/misc/lan966x_pci.c    | 3 ++-
 drivers/of/of_kunit_helpers.c | 2 +-
 drivers/of/overlay.c          | 7 ++++++-
 drivers/of/unittest.c         | 4 ++--
 include/linux/of.h            | 6 ++++--
 5 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/misc/lan966x_pci.c b/drivers/misc/lan966x_pci.c
index 9c79b58137e5..f05cb040ec69 100644
--- a/drivers/misc/lan966x_pci.c
+++ b/drivers/misc/lan966x_pci.c
@@ -128,7 +128,8 @@ static int lan966x_pci_load_overlay(struct lan966x_pci *data)
 	u32 dtbo_size = __dtbo_lan966x_pci_end - __dtbo_lan966x_pci_begin;
 	void *dtbo_start = __dtbo_lan966x_pci_begin;
 
-	return of_overlay_fdt_apply(dtbo_start, dtbo_size, &data->ovcs_id, dev_of_node(data->dev));
+	return of_overlay_fdt_apply(dtbo_start, dtbo_size, &data->ovcs_id,
+				    dev_of_node(data->dev), NULL);
 }
 
 static void lan966x_pci_unload_overlay(struct lan966x_pci *data)
diff --git a/drivers/of/of_kunit_helpers.c b/drivers/of/of_kunit_helpers.c
index 7b3ed5a382aa..476b43474168 100644
--- a/drivers/of/of_kunit_helpers.c
+++ b/drivers/of/of_kunit_helpers.c
@@ -56,7 +56,7 @@ int of_overlay_fdt_apply_kunit(struct kunit *test, void *overlay_fdt,
 		return -ENOMEM;
 
 	ret = of_overlay_fdt_apply(overlay_fdt, overlay_fdt_size,
-				   ovcs_id, NULL);
+				   ovcs_id, NULL, NULL);
 	if (ret)
 		return ret;
 
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index aa1b97e634aa..73ff38c41de2 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -968,6 +968,10 @@ static int of_overlay_apply(struct overlay_changeset *ovcs,
  * @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
+ * @export_symbols_name:
+ *			Name of the export symbol subnode of the @base node to
+ *			provide extra symbols. Those extra symbols are used in
+ *			the overlay symbols resolution.
  *
  * Creates and applies an overlay changeset.
  *
@@ -983,7 +987,8 @@ static int of_overlay_apply(struct overlay_changeset *ovcs,
  */
 
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
-			 int *ret_ovcs_id, const struct device_node *base)
+			 int *ret_ovcs_id, const struct device_node *base,
+			 const char *export_symbols_name)
 {
 	void *new_fdt;
 	void *new_fdt_align;
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 658690fd6980..11091b0176e0 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -3858,7 +3858,7 @@ static int __init overlay_data_apply(const char *overlay_name, int *ovcs_id)
 		pr_err("no overlay data for %s\n", overlay_name);
 
 	ret = of_overlay_fdt_apply(info->dtbo_begin, size, &info->ovcs_id,
-				   NULL);
+				   NULL, NULL);
 	if (ovcs_id)
 		*ovcs_id = info->ovcs_id;
 	if (ret < 0)
@@ -4198,7 +4198,7 @@ static int testdrv_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	}
 
 	size = info->dtbo_end - info->dtbo_begin;
-	ret = of_overlay_fdt_apply(info->dtbo_begin, size, &ovcs_id, dn);
+	ret = of_overlay_fdt_apply(info->dtbo_begin, size, &ovcs_id, dn, NULL);
 	of_node_put(dn);
 	if (ret)
 		return ret;
diff --git a/include/linux/of.h b/include/linux/of.h
index a62154aeda1b..d8e0dd210e09 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -1749,7 +1749,8 @@ struct of_overlay_notify_data {
 #ifdef CONFIG_OF_OVERLAY
 
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
-			 int *ovcs_id, const struct device_node *target_base);
+			 int *ovcs_id, const struct device_node *target_base,
+			 const char *export_symbols_name);
 int of_overlay_remove(int *ovcs_id);
 int of_overlay_remove_all(void);
 
@@ -1759,7 +1760,8 @@ int of_overlay_notifier_unregister(struct notifier_block *nb);
 #else
 
 static inline int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
-				       int *ovcs_id, const struct device_node *target_base)
+				       int *ovcs_id, const struct device_node *target_base,
+				       const char *export_symbols_name)
 {
 	return -ENOTSUPP;
 }
-- 
2.49.0

[PATCH 6/7] of: overlay: Add support for the export symbols node

[Herve Codina]

The resolver already supports the use of the export symbol node.

Add support of the export symbol node feature in of_overlay_fdt_apply()
simply getting the export node from its name and passing it to the
resolver.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 drivers/of/overlay.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 73ff38c41de2..7c55d39f89af 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -891,6 +891,10 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
  * of_overlay_apply() - Create and apply an overlay changeset
  * @ovcs:	overlay changeset
  * @base:	point to the target node to apply overlay
+ * @export_symbols_name:
+ *		Name of the export symbol subnode of the @base node to
+ *		provide extra symbols. Those extra symbols are used in
+ *		the overlay symbols resolution.
  *
  * Creates and applies an overlay changeset.
  *
@@ -915,11 +919,24 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
  */
 
 static int of_overlay_apply(struct overlay_changeset *ovcs,
-			    const struct device_node *base)
+			    const struct device_node *base,
+			    const char *export_symbols_name)
 {
+	struct device_node *export_symbols = NULL;
 	int ret = 0, ret_revert, ret_tmp;
 
-	ret = of_resolve_phandles(ovcs->overlay_root, NULL);
+	if (base && export_symbols_name) {
+		export_symbols = of_get_child_by_name(base, export_symbols_name);
+		if (!export_symbols) {
+			pr_err("overlay get export symbols '%s' from %pOF failed\n",
+			       export_symbols_name, base);
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+
+	ret = of_resolve_phandles(ovcs->overlay_root, export_symbols);
+	of_node_put(export_symbols);
 	if (ret)
 		goto out;
 
@@ -1059,7 +1076,7 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	}
 	ovcs->overlay_mem = overlay_mem;
 
-	ret = of_overlay_apply(ovcs, base);
+	ret = of_overlay_apply(ovcs, base, export_symbols_name);
 	/*
 	 * If of_overlay_apply() error, calling free_overlay_changeset() may
 	 * result in a memory leak if the apply partly succeeded, so do NOT
-- 
2.49.0

[PATCH 7/7] of: unittest: Add tests for export symbols

[Herve Codina]

The export symbols feature allows to use some additional symbols
provided in an export symbols node to resolve overlay symbols.

Add tests to exercise the export symbols feature.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Tested-by: Ayush Singh <ayush@beagleboard.org>
---
 drivers/of/unittest-data/Makefile             |  5 ++
 .../unittest-data/overlay_export_symbols.dtso | 15 +++++
 .../of/unittest-data/testcases_common.dtsi    |  1 +
 .../unittest-data/tests-export-symbols.dtsi   | 30 +++++++++
 drivers/of/unittest.c                         | 65 +++++++++++++++++++
 5 files changed, 116 insertions(+)
 create mode 100644 drivers/of/unittest-data/overlay_export_symbols.dtso
 create mode 100644 drivers/of/unittest-data/tests-export-symbols.dtsi

diff --git a/drivers/of/unittest-data/Makefile b/drivers/of/unittest-data/Makefile
index 01a966e39f23..b51be046749a 100644
--- a/drivers/of/unittest-data/Makefile
+++ b/drivers/of/unittest-data/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_OF_OVERLAY) += overlay.dtbo.o \
 			    overlay_gpio_04a.dtbo.o \
 			    overlay_gpio_04b.dtbo.o \
 			    overlay_pci_node.dtbo.o \
+			    overlay_export_symbols.dtbo.o \
 			    overlay_bad_unresolved.dtbo.o
 
 # enable creation of __symbols__ node
@@ -66,6 +67,10 @@ DTC_FLAGS_testcases += -Wno-interrupts_property \
 #			  overlay_bad_add_dup_prop.dtbo \
 #			  overlay_bad_phandle.dtbo \
 #			  overlay_bad_symbol.dtbo \
+#
+# Also overlay_export_symbols_ovl.dtbo is designed to be applied to a specific
+# node and cannot be applied statically with fdtoverlay
+
 
 apply_static_overlay_1 := overlay_0.dtbo \
 			  overlay_1.dtbo \
diff --git a/drivers/of/unittest-data/overlay_export_symbols.dtso b/drivers/of/unittest-data/overlay_export_symbols.dtso
new file mode 100644
index 000000000000..89c9df4ef89b
--- /dev/null
+++ b/drivers/of/unittest-data/overlay_export_symbols.dtso
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+/dts-v1/;
+/plugin/;
+
+/ {
+	fragment@0 {
+		target-path="";
+		__overlay__ {
+			ovl_node {
+				ref-base = <&test_export_base>;
+				ref-node = <&test_export_node>;
+			};
+		};
+	};
+};
diff --git a/drivers/of/unittest-data/testcases_common.dtsi b/drivers/of/unittest-data/testcases_common.dtsi
index 1c2cdf353ae3..21ffe0fb03ef 100644
--- a/drivers/of/unittest-data/testcases_common.dtsi
+++ b/drivers/of/unittest-data/testcases_common.dtsi
@@ -18,4 +18,5 @@ node-remove {
 #include "tests-address.dtsi"
 #include "tests-platform.dtsi"
 #include "tests-overlay.dtsi"
+#include "tests-export-symbols.dtsi"
 #include "tests-lifecycle.dtsi"
diff --git a/drivers/of/unittest-data/tests-export-symbols.dtsi b/drivers/of/unittest-data/tests-export-symbols.dtsi
new file mode 100644
index 000000000000..1650289b34cd
--- /dev/null
+++ b/drivers/of/unittest-data/tests-export-symbols.dtsi
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/ {
+	testcase-data {
+		test-export-symbols {
+			test_export_symbols_b0: base0 {
+				test_export_symbols_n0: node {
+					dummy;
+				};
+
+				export-symbols {
+					test_export_base = <&test_export_symbols_b0>;
+					test_export_node = <&test_export_symbols_n0>;
+				};
+			};
+
+			test_export_symbols_b1: base1 {
+
+				test_export_symbols_n1: node {
+					dummy;
+				};
+
+				export-symbols {
+					test_export_base = <&test_export_symbols_b1>;
+					test_export_node = <&test_export_symbols_n1>;
+				};
+			};
+		};
+	};
+};
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 11091b0176e0..bf286902c65b 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -4164,6 +4164,69 @@ static __init void of_unittest_overlay_high_level(void)
 	mutex_unlock(&of_mutex);
 }
 
+OVERLAY_INFO_EXTERN(overlay_export_symbols);
+
+static __init void of_unittest_export_symbols(const char *prefix,
+					      const char *base_full_path)
+{
+	const struct overlay_info ovl = OVERLAY_INFO(overlay_export_symbols, 0, 0);
+	struct device_node *ovl_node;
+	struct device_node *base;
+	struct device_node *node;
+	struct device_node *ref;
+	int ovcs_id;
+	u32 size;
+	int ret;
+
+	base = of_find_node_by_path(base_full_path);
+	if (unittest(base, "%s: Get base (%s) failed\n", prefix, base_full_path))
+		return;
+
+	node = of_get_child_by_name(base, "node");
+	if (unittest(base, "%s: Get node from %pOF failed\n", prefix, base))
+		goto end_put_base;
+
+	size = ovl.dtbo_end - ovl.dtbo_begin;
+	ret = of_overlay_fdt_apply(ovl.dtbo_begin, size, &ovcs_id, base, "export-symbols");
+	if (unittest(!ret, "%s: Apply '%s' failed (%d)\n", prefix, ovl.name, ret))
+		goto end_put_node;
+
+	ovl_node = of_get_child_by_name(base, "ovl_node");
+	if (unittest(ovl_node, "%s: Get ovl_node from %pOF failed\n", prefix, base))
+		goto end_remove_overlay;
+
+	ref = of_parse_phandle(ovl_node, "ref-base", 0);
+	if (unittest(ref, "%s: Parse 'ref-base' from %pOF failed\n", prefix, ovl_node))
+		goto end_put_ovl_node;
+	unittest(ref == base,
+		 "%s: Node from 'ref-base' phandle mismatches (got %pOF, expected %pOF)\n",
+		 prefix, ref, base);
+	of_node_put(ref);
+
+	ref = of_parse_phandle(ovl_node, "ref-node", 0);
+	if (unittest(ref, "%s: Parse 'ref-node' from %pOF failed\n", prefix, ovl_node))
+		goto end_put_ovl_node;
+	unittest(ref == node,
+		 "%s: Node from 'ref-node' phandle mismatches (got %pOF, expected %pOF)\n",
+		 prefix, ref, node);
+	of_node_put(ref);
+
+end_put_ovl_node:
+	of_node_put(ovl_node);
+end_remove_overlay:
+	of_overlay_remove(&ovcs_id);
+end_put_node:
+	of_node_put(node);
+end_put_base:
+	of_node_put(base);
+}
+
+static __init void of_unittest_overlay_export_symbols(void)
+{
+	of_unittest_export_symbols("base0", "/testcase-data/test-export-symbols/base0");
+	of_unittest_export_symbols("base1", "/testcase-data/test-export-symbols/base1");
+}
+
 static int of_unittest_pci_dev_num;
 static int of_unittest_pci_child_num;
 
@@ -4349,6 +4412,7 @@ static void __init of_unittest_pci_node(void)
 #else
 
 static inline __init void of_unittest_overlay_high_level(void) {}
+static inline __init void of_unittest_overlay_export_symbols(void) {}
 static inline __init void of_unittest_pci_node(void) { }
 
 #endif
@@ -4404,6 +4468,7 @@ static int __init of_unittest(void)
 	of_unittest_overlay();
 	of_unittest_lifecycle();
 	of_unittest_pci_node();
+	of_unittest_overlay_export_symbols();
 
 	/* Double check linkage after removing testcase data */
 	of_unittest_check_tree_linkage();
-- 
2.49.0

Re: [PATCH 0/7] of: overlay: Add support for export-symbols node feature

[Herve Codina]

Hi all,

Sorry, this should be a v2 series.

I resend as v2.

Please ighnore this one.

Best regards,
Hervé


On Wed, 30 Apr 2025 14:48:59 +0200
Herve Codina <herve.codina@bootlin.com> wrote:

> Hi,
> 
> At Linux Plumbers Conference 2024, we (me and Luca Ceresolli) talked
> about issues we have with runtime hotplug on non-discoverable busses
> with device tree overlays [1].
> 
> On our system, a base board has a connector and addon boards can be
> connected to this connector. Both boards are described using device
> tree. The base board is described by a base device tree and addon boards
> are describe by overlays device tree. More details can be found at [2].
> 
> This kind of use case can be found also on:
>   - Grove Sunlight Sensor [3]
>   - mikroBUS [4]
> 
> One of the issue we were facing on was referencing resources available
> on the base board device tree from the addon overlay device tree.
> 
> Using a nexus node [5] helps decoupling resources and avoid the
> knowledge of the full base board from the overlay. Indeed, with nexus
> node, the overlay need to know only about the nexus node itself.
> 
> For instance, suppose a connector where a GPIO is connected at PinA. On
> the base board this GPIO is connected to the GPIO 12 of the SoC GPIO
> controller.
> 
> The base board can describe this GPIO using a nexus node:
>     soc_gpio: gpio-controller {
>       #gpio-cells = <2>;
>     };
> 
>     connector1: connector1 {
>         /*
>          * Nexus node for the GPIO available on the connector.
>          * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
>          * controller
>          */
>         #gpio-cells = <2>;
>         gpio-map = <0 0 &soc_gpio 12 0>;
>         gpio-map-mask = <0xf 0x0>;
>         gpio-map-pass-thru = <0x0 0xf>;
>     };
> 
> The connector pin A GPIO can be referenced using:
>   <&connector1 0 GPIO_ACTIVE_HIGH>
> 
> This implies that the overlay needs to know about exact label that
> references the connector. This label can be different on a different
> board and so applying the overlay could failed even if it is used to
> describe the exact same addon board. Further more, a given base board
> can have several connectors where the exact same addon board can be
> connected. In that case, the same overlay cannot be used on both
> connector. Indeed, the connector labels have to be different.
> 
> The export-symbols node introduced by this current series solves this
> issue.
> 
> The idea of export-symbols is to have something similar to the global
> __symbols__ node but local to a specific node. Symbols listed in this
> export-symbols are local and visible only when an overlay is applied on
> a node having an export-symbols subnode.
> 
> Using export-symbols, our example becomes:
>     soc_gpio: gpio-controller {
>       #gpio-cells = <2>;
>     };
> 
>     connector1: connector1 {
>         /*
>          * Nexus node for the GPIO available on the connector.
>          * GPIO 0 (Pin A GPIO) is connected to GPIO 12 of the SoC gpio
>          * controller
>          */
>         #gpio-cells = <2>;
>         gpio-map = <0 0 &soc_gpio 12 0>;
>         gpio-map-mask = <0xf 0x0>;
>         gpio-map-pass-thru = <0x0 0xf>;
> 
>         export-symbols {
>           connector = <&connector1>;
>         };
>     };
> 
> With that export-symbols node, an overlay applied on connector1 node can
> have the symbol named 'connector' resolved to connector1. Indeed, the
> export-symbols node available at connector1 node is used when the
> overlay is applied. If the overlay has an unresolved 'connector' symbol,
> it will be resolved to connector1 thanks to export-symbols.
> 
> Our overlay using the nexus node can contains:
>    node {
>       foo-gpio = <&connector 0 GPIO_ACTIVE_HIGH>;
>    };
> It used the GPIO 0 from the connector it is applied on.
> 
> A board with two connectors can be described with:
>     connector1: connector1 {
>         ...
>         export-symbols {
>           connector = <&connector1>;
>         };
>     };
> 
>     connector2: connector2 {
>         ...
>         export-symbols {
>           connector = <&connector2>;
>         };
>     };
> 
> In that case, the same overlay with unresolved 'connector' symbol can be
> applied on both connectors and the correct symbol resolution (connector1
> or connector2) will be done.
> 
> This current series add support for the export-symbols node feature:
>   - Patch 1 describes the export-symbols binding
>   - Patches 2 to 6 prepare and add the support for the export-symbols
>     feature
>   - Patch 7 adds an unittest for the export-symbols feature
> 
> Compare to the previous iteration, the series has been rebased on
> top of v6.15-rc1 and an compilation issue in unittest has been fixed.
> 
> Also it is worth noting the work already done by Ayush Singh related to
> this topic on other repositories:
>   - Add export-symbols in device-tree specification
>       [PATCH v3] Add new `export-symbols` node [6]
> 
>   - Support for export-symbols in the device tree compiler
>       [PATCH 0/3] Allow specifying target node in fdtoverlay [7]
>       [PATCH] checks: Add support for export-symbols [8]
> 
> Best regards,
> Hervé
> 
> [1] https://lpc.events/event/18/contributions/1696/
> [2] https://lore.kernel.org/lkml/20240917-hotplug-drm-bridge-v4-0-bc4dfee61be6@bootlin.com/
> [3] https://lore.kernel.org/lkml/20240702164403.29067-1-afd@ti.com/
> [4] https://lore.kernel.org/lkml/20240627-mikrobus-scratch-spi-v5-0-9e6c148bf5f0@beagleboard.org/
> [5] https://github.com/devicetree-org/devicetree-specification/blob/v0.4/source/chapter2-devicetree-basics.rst#nexus-nodes-and-specifier-mapping
> [6] https://lore.kernel.org/all/20250411-export-symbols-v3-1-f59368d97063@beagleboard.org/
> [7] https://lore.kernel.org/all/20250313-fdtoverlay-target-v1-0-dd5924e12bd3@beagleboard.org/
> [8] https://lore.kernel.org/all/20250110-export-symbols-v1-1-b6213fcd6c82@beagleboard.org/
> 
> Changes v1 -> v2
>   v1: https://lore.kernel.org/all/20241209151830.95723-1-herve.codina@bootlin.com/
> 
>   - All patches
>     Add 'Tested-by: Ayush Singh <ayush@beagleboard.org>'
> 
>   - Patch 1
>     Update the 'patternProperties' regexp
> 
>   - Patch 2 and 4
>     Fix conflicts due to the rebase on top of v6.15-rc1
> 
>   - Patch 5
>     Fix a typo in commit log
> 
>   - Patch 7
>     Fix a compilation issue detected by a kernel test robot
> 
> Herve Codina (7):
>   dt-bindings: Add support for export-symbols node
>   of: resolver: Introduce get_phandle_from_symbols_node()
>   of: resolver: Add export_symbols in of_resolve_phandles() parameters
>   of: resolver: Add support for the export symbols node
>   of: overlay: Add export_symbols_name in of_overlay_fdt_apply()
>     parameters
>   of: overlay: Add support for the export symbols node
>   of: unittest: Add tests for export symbols
> 
>  .../devicetree/bindings/export-symbols.yaml   | 43 +++++++++++
>  drivers/misc/lan966x_pci.c                    |  3 +-
>  drivers/of/of_kunit_helpers.c                 |  2 +-
>  drivers/of/of_private.h                       |  2 +-
>  drivers/of/overlay.c                          | 30 +++++++-
>  drivers/of/resolver.c                         | 75 ++++++++++++++----
>  drivers/of/unittest-data/Makefile             |  5 ++
>  .../unittest-data/overlay_export_symbols.dtso | 15 ++++
>  .../of/unittest-data/testcases_common.dtsi    |  1 +
>  .../unittest-data/tests-export-symbols.dtsi   | 30 ++++++++
>  drivers/of/unittest.c                         | 77 +++++++++++++++++--
>  include/linux/of.h                            |  6 +-
>  12 files changed, 258 insertions(+), 31 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/export-symbols.yaml
>  create mode 100644 drivers/of/unittest-data/overlay_export_symbols.dtso
>  create mode 100644 drivers/of/unittest-data/tests-export-symbols.dtsi
> 



-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com