linux-kernel - [PATCH] docs: dt: writing-schema: Describe defining properties in top-level

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Message-ID: <20250904142400.179955-2-krzysztof.kozlowski@linaro.org>
Date: Thu,  4 Sep 2025 16:24:01 +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] docs: dt: writing-schema: Describe defining properties in top-level

Document established Devicetree bindings maintainers review practice:
Properties having differences per each device in the binding, e.g.
different constraints for lists or different allowed values, should
still be defined in top-level 'properties' section and only customized
in 'if:then:'.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
---
 Documentation/devicetree/bindings/writing-schema.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/writing-schema.rst b/Documentation/devicetree/bindings/writing-schema.rst
index 470d1521fa17..e0859094575d 100644
--- a/Documentation/devicetree/bindings/writing-schema.rst
+++ b/Documentation/devicetree/bindings/writing-schema.rst
@@ -165,6 +165,14 @@ The YAML Devicetree format also makes all string values an array and scalar
 values a matrix (in order to define groupings) even when only a single value
 is present. Single entries in schemas are fixed up to match this encoding.
 
+When bindings cover multiple similar devices that differ in some properties,
+those properties should be constrained for each device. This usually means:
+
+ * In top level 'properties' define the property with the broadest constraints.
+ * In 'if:then:' blocks, further narrow the constraints for those properties.
+ * Do not define the properties within an 'if:then:' block (note that
+   'additionalItems' also won't allow that).
+
 Coding style
 ------------
 
-- 
2.48.1