linux-kernel - Re: [PATCH 02/14] dt-bindings: phy: qcom,qmp-usb3-dp: fix sc8280xp bindings

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Date:   Mon, 14 Nov 2022 17:56:21 +0100
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>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/14] dt-bindings: phy: qcom,qmp-usb3-dp: fix sc8280xp
 bindings

On 14/11/2022 17:48, Johan Hovold wrote:
> On Mon, Nov 14, 2022 at 05:39:26PM +0100, Krzysztof Kozlowski wrote:
>> On 14/11/2022 17:32, Johan Hovold wrote:
> 
>>> Fair enough, I'll drop it. But there doesn't seem to be a good way to
>>> describe the indexes currently and most bindings simply ignore to do so.
>>>
>>> So what is the preference then? Just leave things undocumented, listing
>>> indexes in a free-text 'description', or adding a free-text reference to
>>> a binding header file and using those define names in a free-text
>>> 'description'?
>>
>> Either 2 or 3. Several bindings for small number of constants choose
>> option 2.
> 
> Ok, we have three now, but USB4 will bump this to ten or so.

Then probably header file is the way to go.

>  
>>> And if going with the last option, does this mean that every SoC and PHY
>>> type needs its own header for those three clocks or so to avoid having
>>> a common dumping ground header file where indexes will not necessarily
>>> be 0-based and consecutive.
>>
>> phy-qcom-qmp-combo.c has one qcom_qmp_dp_clks_hw_get(), so why would you
>> have many of header files?
> 
> We don't know what kind of clock outputs later revisions of these PHYs
> will have. The only way to guarantee 0-based consecutive indexes appears
> to be to use per-SoC defines (e.g. as for the GCC bindings).

Which is also fine. I don't understand still why it is a problem - even
if you have multiple files, one for each SoC/phy. If USB4 brings here 10
more clocks and other SoCs/phys might bring many more options, then what
else can you do? Grow the binding file with big text-based mapping of
IDs? It's not a viable solution. Header or headers is the only
maintainable way for such cases.

Best regards,
Krzysztof