Re: [PATCH] docs: dt: writing-bindings: Extend compatible fallbacks guideline

[Conor Dooley <conor@kernel.org>]

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On Wed, Apr 15, 2026 at 10:21:14AM +0200, Krzysztof Kozlowski wrote:
> Extend the guidelines when to use fallback compatibles to cover to
> common review responses.  Devices are most likely compatible and should
> use fallbacks when having:
> 
> 1. Compatible programming interface, meaning one is a subset, and Linux
>    device drivers can use the subset to correctly match/bind and still
>    operate with the subset features.
> 
> 2. Device variant discovery through some means, like registers.
> 
> Devices are incompatible and fallback is not suitable when that
> fallback cannot be used by the drivers to match/bind.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
> ---
>  Documentation/devicetree/bindings/writing-bindings.rst | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/writing-bindings.rst b/Documentation/devicetree/bindings/writing-bindings.rst
> index 667816dd7d50..03e29e2d50af 100644
> --- a/Documentation/devicetree/bindings/writing-bindings.rst
> +++ b/Documentation/devicetree/bindings/writing-bindings.rst
> @@ -53,7 +53,12 @@ Properties
>     - DON'T use wildcards or device-family names in compatible strings.
>  
>     - DO use fallback compatibles when devices are the same as or a superset of
> -     prior implementations.
> +     prior implementations.  Fallback compatibles are applicable especially
> +     when sharing a programming interface or when able to discover the
> +     variants.
> +
> +   - DON'T add fake fallback compatibles when software cannot use such to match
> +     and bind to a device, and still operate correctly.
>  
>     - DO add new compatibles in case there are new features or bugs.

Acked-by: Conor Dooley <conor.dooley@microchip.com>

     - DO use the commit message explain why devices that may appear
       compatible in a diff (e.g. no differences in property use) but
       are not compatible, are not compatible.

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