Re: [PATCH] dt-bindings: examples: Add GPIO hogs and variable-lists

[Rob Herring <robh@kernel.org>]

On Thu, Sep 26, 2024 at 03:42:18PM +0200, Krzysztof Kozlowski wrote:
> Same Devicetree binding can be expressed multiple ways thus no wonder
> we have multiple variants of similar concept.  All such code could be
> cleaned up, but even then new contributor might not be able to find
> good, existing binding solving their case.
> 
> Add subdirectory with two Devicetree schema examples (GPIO hog and
> variable lists like clocks), hoping it will grow with reference-designs.
> All these bindings use valid compatibles, although with "test" vendor
> prefix, so they will be validated by DT schema.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> 
> ---
> 
> If approach is accepted, I will come with more ideas, as commented
> during LPC DT BoF to creates examples based on review.
> 
> Cc: Nishanth Menon <nm@ti.com>
> Cc: Bjorn Andersson <andersson@kernel.org>
> ---
>  .../devicetree/bindings/example-schema.yaml   |   2 +
>  .../examples/gpio-controller-and-hogs.yaml    |  72 ++++++++++++
>  .../multiple-variants-and-variable-lists.yaml | 110 ++++++++++++++++++
>  .../devicetree/bindings/writing-schema.rst    |   6 +-
>  4 files changed, 189 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/devicetree/bindings/examples/gpio-controller-and-hogs.yaml
>  create mode 100644 Documentation/devicetree/bindings/examples/multiple-variants-and-variable-lists.yaml
> 
> diff --git a/Documentation/devicetree/bindings/example-schema.yaml b/Documentation/devicetree/bindings/example-schema.yaml
> index a41f9b9a196b..0aece1823fde 100644
> --- a/Documentation/devicetree/bindings/example-schema.yaml
> +++ b/Documentation/devicetree/bindings/example-schema.yaml
> @@ -25,6 +25,8 @@ description: |
>    indentation less than the first line of the literal block. Lines also cannot
>    begin with a tab character.
>  
> +  See also examples/ subdirectory for more detailed code snippets.
> +
>  select: false
>    # 'select' is a schema applied to a DT node to determine if this binding
>    # schema should be applied to the node. It is optional and by default the
> diff --git a/Documentation/devicetree/bindings/examples/gpio-controller-and-hogs.yaml b/Documentation/devicetree/bindings/examples/gpio-controller-and-hogs.yaml
> new file mode 100644
> index 000000000000..597a847daa12
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/examples/gpio-controller-and-hogs.yaml
> @@ -0,0 +1,72 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/examples/gpio-controller-and-hogs.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: An Example GPIO Controller with Hogs
> +
> +maintainers:
> +  - Rob Herring <robh@kernel.org>
> +  - Krzysztof Kozlowski <krzk@kernel.org>
> +  - Conor Dooley <conor@kernel.org>
> +
> +properties:
> +  compatible:
> +    const: test,gpio-controller-and-hogs
> +
> +  gpio-controller: true
> +
> +  "#gpio-cells":
> +    const: 2
> +
> +  gpio-line-names:
> +    minItems: 1
> +    maxItems: 32
> +
> +  gpio-ranges:
> +    minItems: 1
> +    maxItems: 16
> +
> +  # Not every GPIO controller is an interrupt-controller
> +  interrupt-controller: true
> +
> +  "#interrupt-cells":
> +    const: 2
> +
> +patternProperties:
> +  "-hog(-[0-9]+)?$":
> +    type: object
> +    required:
> +      - gpio-hog

The best way to ensure this is done right is eliminate the need rather 
than adding examples to be ignored.

I think we need to make gpio provider bindings reference gpio.yaml and 
then handle hogs there. Generally, the pattern is that providers which 
just list properties don't have a $ref to the provider schema and are 
always applied. Schemas that have child nodes like bus schemas are 
referenced by the specific controller schemas. GPIO started out as the 
former, but the addition of hogs made it more like the latter. That of 
course means that every GPIO provider can have hogs, but I think that's 
the right answer even though I'd really prefer no hogs at all.

Always applying schemas like gpio.yaml has some benefits over relying 
on applying it via $ref, but that's diminished once everything has a 
schema. Of course, we can do both at the expense of applying the schema 
twice.

Rob