linux-kernel - [PATCH] dt-bindings: writing-schema: Explain sub-nodes with additionalProperties:true

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Message-ID: <20250331081345.37103-1-krzysztof.kozlowski@linaro.org>
Date: Mon, 31 Mar 2025 10:13:45 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: [PATCH] dt-bindings: writing-schema: Explain sub-nodes with additionalProperties:true

Document recently introduced pattern of using additionalProperties: true
for sub-nodes with their own schema.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
---
 .../devicetree/bindings/example-schema.yaml       | 15 ++++++++++++++-
 .../devicetree/bindings/writing-schema.rst        | 11 ++++++++---
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/example-schema.yaml b/Documentation/devicetree/bindings/example-schema.yaml
index 484f8babcda4..c731d5045e80 100644
--- a/Documentation/devicetree/bindings/example-schema.yaml
+++ b/Documentation/devicetree/bindings/example-schema.yaml
@@ -178,7 +178,9 @@ properties:
     description: Child nodes are just another property from a json-schema
       perspective.
     type: object  # DT nodes are json objects
-    # Child nodes also need additionalProperties or unevaluatedProperties
+    # Child nodes also need additionalProperties or unevaluatedProperties, where
+    # 'false' should be used in most cases (see 'child-node-with-own-schema'
+    # below).
     additionalProperties: false
     properties:
       vendor,a-child-node-property:
@@ -189,6 +191,17 @@ properties:
     required:
       - vendor,a-child-node-property
 
+  child-node-with-own-schema:
+    description: |
+      Child node with their own compatible and device schema which ends in
+      'additionalProperties: false' or 'unevaluatedProperties: false' can
+      mention only the compatible and use here 'additionalProperties: true'.
+    type: object
+    additionalProperties: true
+    properties:
+      compatible:
+        const: vendor,sub-device
+
 # Describe the relationship between different properties
 dependencies:
   # 'vendor,bool-property' is only allowed when 'vendor,string-array-property'
diff --git a/Documentation/devicetree/bindings/writing-schema.rst b/Documentation/devicetree/bindings/writing-schema.rst
index eb8ced400c7e..fc73072f12fc 100644
--- a/Documentation/devicetree/bindings/writing-schema.rst
+++ b/Documentation/devicetree/bindings/writing-schema.rst
@@ -117,9 +117,14 @@ additionalProperties / unevaluatedProperties
       should be allowed.
 
   * additionalProperties: true
-      Rare case, used for schemas implementing common set of properties. Such
-      schemas are supposed to be referenced by other schemas, which then use
-      'unevaluatedProperties: false'.  Typically bus or common-part schemas.
+      - Top-level part:
+        Rare case, used for schemas implementing common set of properties. Such
+        schemas are supposed to be referenced by other schemas, which then use
+        'unevaluatedProperties: false'.  Typically bus or common-part schemas.
+      - Nested node:
+        When listing only the expected compatible of the nested node and there
+        is an another schema matching that compatible which ends with one of
+        two above cases ('false').
 
 examples
   Optional. A list of one or more DTS hunks implementing this binding only.
-- 
2.43.0