[PATCH v2 4/5] dt-bindings/perf: Add Arm CoreSight PMU

[Robin Murphy]

On 2023-12-18 7:03 am, Krzysztof Kozlowski wrote:
> On 15/12/2023 19:39, Robin Murphy wrote:
>>>> +required:
>>>> +  - compatible
>>>> +  - reg
>>>> +
>>>> +additionalProperties: false
>>>
>>> Why no example to validate the binding?
>>
>> IMO for such a trivial binding built out of common properties, an
>> equally trivial example isn't going to add any value, since it won't do
>> anything more than re-state the individual property definitions above.
>> In bindings where we have conditional relationships between properties,
>> or complex encodings where a practical example can help explain a
>> definition (e.g. a map/mask pair for a set of input values), then
>> absolutely, an example can add something more to help the author and/or
>> users. But otherwise, the thing I've really grown to like about schema
>> is how thoroughly self-describing the definitions themselves can now be.
> 
> The example is used to validate the schema.

Can you clarify what that *means*, though? As far as I can tell from a 
bit of experimentation, "make dt_bindings_check" picks up errors in the 
schema definition itself just the same whether an example is present or 
not. Thus I still fail to understand what else would be validated by me 
writing an example here, other than my personal ability to comprehend my 
own binding.

Yes, I'm well aware that back when we were bootstrapping dtschema it was 
useful to confirm that schemas were written to correctly describe 
*existing* known-good DT fragments. However with new bindings like this 
we've already reached the end goal, where we write an authoritative 
schema first, then the users follow from there. As I alluded to above, 
there are reasons why I would actually prefer *not* to provide a usage 
example here - frankly if a user doesn't understand which parts of the 
architecture their hardware implements, and/or can't figure out how to 
copy a single compatible string and write a standard reg property, I 
would much rather they come to me asking how to write a DT entry, than 
blindly copy-paste a verbatim example into their DTS, then come to me 
reporting a "bug" with the driver crashing or failing to probe. I'd love 
to say I have no experience to base that judgement on, but...

Thanks,
Robin.