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

[Krzysztof Kozlowski]

On 27/04/2026 16:37, Rob Herring wrote:
> On Wed, Apr 15, 2026 at 03:46:41PM +0100, Conor Dooley wrote:
>> 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@xxxxxxxxxxxxxxxx>
>>> ---
>>>  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@xxxxxxxxxxxxx>
>>
>>      - 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.
> 
> Can you respin with Conor's addition.

Ack

Best regards,
Krzysztof