linux-kernel - Re: [PATCH 17/43] dt-bindings: phy: qcom,qmp-pcie: add missing child node schema

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Date:   Tue, 5 Jul 2022 20:21:12 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 17/43] dt-bindings: phy: qcom,qmp-pcie: add missing child
 node schema

On 05/07/2022 14:11, Johan Hovold wrote:
> On Tue, Jul 05, 2022 at 01:56:32PM +0200, Krzysztof Kozlowski wrote:
>> On 05/07/2022 13:51, Johan Hovold wrote:
>>> On Tue, Jul 05, 2022 at 12:18:37PM +0200, Krzysztof Kozlowski wrote:
>>>> On 05/07/2022 11:42, Johan Hovold wrote:
>>>>> Add the missing the description of the PHY-provider child node which was
>>>>> ignored when converting to DT schema.
>>>>>
>>>>> Also fix up the incorrect description that claimed that one child node
>>>>> per lane was required.
>>>>>
>>>>> Fixes: ccf51c1cedfd ("dt-bindings: phy: qcom,qmp: Convert QMP PHY bindings to yaml")
>>>>> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
>>>>> ---
>>>>>  .../bindings/phy/qcom,qmp-pcie-phy.yaml       | 88 ++++++++++++++++++-
>>>>>  1 file changed, 85 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/phy/qcom,qmp-pcie-phy.yaml b/Documentation/devicetree/bindings/phy/qcom,qmp-pcie-phy.yaml
>>>>> index ff1577f68a00..5a1ebf874559 100644
>>>>> --- a/Documentation/devicetree/bindings/phy/qcom,qmp-pcie-phy.yaml
>>>>> +++ b/Documentation/devicetree/bindings/phy/qcom,qmp-pcie-phy.yaml
>>>>> @@ -69,9 +69,37 @@ properties:
>>>
>>>>> +  - if:
>>>>> +      properties:
>>>>> +        compatible:
>>>>> +          contains:
>>>>> +            enum:
>>>>> +              - qcom,sm8250-qmp-gen3x2-pcie-phy
>>>>> +              - qcom,sm8250-qmp-modem-pcie-phy
>>>>> +              - qcom,sm8450-qmp-gen4x2-pcie-phy
>>>>> +    then:
>>>>> +      patternProperties:
>>>>> +        "^phy@[0-9a-f]+$":
>>>>> +          properties:
>>>>> +            reg:
>>>>> +              items:
>>>>> +                - description: TX lane 1
>>>>> +                - description: RX lane 1
>>>>> +                - description: PCS
>>>>> +                - description: TX lane 2
>>>>> +                - description: RX lane 2
>>>>> +                - description: PCS_MISC
>>>>> +    else:
>>>>> +      patternProperties:
>>>>> +        "^phy@[0-9a-f]+$":
>>>>> +          properties:
>>>>> +            reg:
>>>>> +              minItems: 3
>>>>> +              maxItems: 4
>>>>> +              items:
>>>>> +                - description: TX
>>>>> +                - description: RX
>>>>> +                - description: PCS
>>>>> +                - description: PCS_MISC
>>>>> +      if:
>>>>
>>>> Do not include if within other if. Just split the entire section to its
>>>> own if:.
>>>
>>> That sounds like it would just obfuscate the logic. The else clause
>>> specified 3-4 registers and the nested if determines which compatibles
>>> use which by further narrowing the range.
>>>
>>> If you move it out to the else: this would be really hard understand and
>>> verify.
>>
>> Every bindings are expected to do that way and most of them are doing
>> it: define broad constraints in properties:, then define strict
>> constraints per each variant. Easy to follow code. This binding is not
>> particularly special to make it different than other ones. Doing
>> semi-strict constraints in if: and then additional constrain in nested
>> if: is not easy to understand and verify.
> 
> Ok, so you want to flatten this by repeating also the register
> descriptions?
> 
> That wouldn't hurt readability as much, but doing so would be more error
> prone as it's easy to miss adding a new compatible in every group of
> conditionals and there's no else clause to catch the mistake.
> 
> Right know the logic is
> 
> 	if dual-lane
> 		items = 6
> 	else
> 		items = 3 or 4
> 		if single-lane-exception
> 			items = 3
> 		else
> 			items = 4
> 
> Flattening this gives
> 
> 	if dual-lane
> 		items = 6
> 	if single-lane-normal
> 		items = 4
> 	if single-lane-exception
> 		items = 3
> 
> Which means that every compatible must now be listed in one of the
> conditionals.

Yes, because it's explicit and easy to read. Handling compatibles in
'else' makes it opposite - one cannot use grep and cannot easily find
what is actually covered by maxItems:4 (you need to check all 7
compatibles to find what is not covered here).

> 
> Fine with me, but please confirm that I understood you correctly.

You have already flattened if-if-if for clocks and resets, so this
should follow similar approach. I don't think it could be squashed with
that previous if-if-if, though.

Best regards,
Krzysztof