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

[Frank Li <Frank.li@nxp.com>]

On Fri, Sep 05, 2025 at 08:49:01AM +0200, Krzysztof Kozlowski wrote:
> On 04/09/2025 17:30, Frank Li wrote:
> >> 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).
> >> +
> >
> > I can understand what your said. I think it would be better if add some
> > simple examples.
> Example for that is already there - at the bottom of this file.

example-schema.yaml is big, it is hard to match to this specific rule. some
small section will be helpful

              properties:
                a:               # define 'a' at top
                  enum: [0, 1]   # width range in here
              allOf:
                - if:
                    ...          # some condition
                  then:
                    properties:
                      a:
                        const: 0 # allow only 0 for some specific condition.

Frank


>
> Best regards,
> Krzysztof