linux-kernel - Re: [PATCH 1/2] dt-bindings: PCI: qcom: Add SC8280XP/SA8540P interconnects

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Date:   Thu, 20 Oct 2022 08:29:02 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        quic_vbadigan@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: PCI: qcom: Add SC8280XP/SA8540P
 interconnects

On 20/10/2022 03:57, Johan Hovold wrote:
> On Wed, Oct 19, 2022 at 10:37:31AM -0400, Krzysztof Kozlowski wrote:
>> On 17/10/2022 07:24, Johan Hovold wrote:
>>> Add the missing SC8280XP/SA8540P "pcie-mem" and "cpu-pcie" interconnect
>>> paths to the bindings.
>>>
>>> Fixes: 76d777ae045e ("dt-bindings: PCI: qcom: Add SC8280XP to binding")
>>> Fixes: 76c4207f4085 ("dt-bindings: PCI: qcom: Add SA8540P to binding")
>>> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
>>> ---
>>>  .../devicetree/bindings/pci/qcom,pcie.yaml    | 25 +++++++++++++++++++
>>>  1 file changed, 25 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>> index 22a2aac4c23f..a55434f95edd 100644
>>> --- a/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>> +++ b/Documentation/devicetree/bindings/pci/qcom,pcie.yaml
>>> @@ -62,6 +62,12 @@ properties:
>>>      minItems: 3
>>>      maxItems: 12
>>>  
>>> +  interconnects:
>>> +    maxItems: 2
>>> +
>>> +  interconnect-names:
>>> +    maxItems: 2
>>> +
>>>    resets:
>>>      minItems: 1
>>>      maxItems: 12
>>> @@ -629,6 +635,25 @@ allOf:
>>>            items:
>>>              - const: pci # PCIe core reset
>>>  
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          contains:
>>> +            enum:
>>> +              - qcom,pcie-sa8540p
>>> +              - qcom,pcie-sc8280xp
>>> +    then:
>>> +      properties:
>>> +        interconnects:
>>> +          maxItems: 2
>>
>> No need for this.
>>
>>> +        interconnect-names:
>>> +          items:
>>> +            - const: pcie-mem
>>> +            - const: cpu-pcie
>>> +      required:
>>> +        - interconnects
>>> +        - interconnect-names
>>
>> else:
>>   ??
>>
>> Otherwise, you allow any names for other variants.
> 
> Are you suggesting something like moving the names to the common
> constraints for now:
> 
>   interconnects:
>     maxItems: 2
> 
>   interconnect-names:
>     items:
>       - const: pcie-mem
>       - const: cpu-pcie
> 
> and then in the allOf:
> 
>   - if:
>       properties:
>         compatible:
>           contains:
>             enum:
>               - qcom,pcie-sa8540p
>               - qcom,pcie-sc8280xp
>     then:
>       required:
>         - interconnects
>         - interconnect-names
>     else:
>       properties:
>         interconnects: false
>         interconnect-names: false
> 
> This way we'd catch anyone adding interconnects to a DTS without first
> updating the bindings, but it also seems to go against the idea of
> bindings fully describing the hardware by saying that no other platforms
> have interconnects (when they actually do even if we don't describe it
> just yet).

You can add a comment to the else like "TODO: Not described yet". I
would prefer to have specific but incomplete bindings, instead of loose
one which later might cause people adding whatever names they like.

> Or should we do the above but without the else clause to have some
> constraints in place on the names at least?

This would work as well if you think the names are applicable for other
devices.

Best regards,
Krzysztof