linux-kernel - Re: [PATCH 2/4] arm64: dts: qcom: add SC8280XP platform

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Date:   Wed, 22 Jun 2022 16:44:26 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Johan Hovold <johan+linaro@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] arm64: dts: qcom: add SC8280XP platform

On 22/06/2022 05:32, Bjorn Andersson wrote:
>>>>
>>>
>>> It's an interesting question, but I don't think it's possible to change
>>> the rate of this clock from one board to another.
>>>
>>> So I think it's best to keep this in the .dtsi, to avoid unnecessary
>>> duplication.
>>
>> It does not matter whether the frequency can be changed or not. This is
>> the same on almost every SoC and the same comments appear every time -
>> the clock is a property of the board, not of the SoC, so it should be in
>> the board DTSI. To avoid the duplication you can indeed keep here most
>> of the clock properties, but the frequency must be in board DTS.
>>
> 
> I find this to be a rather strict interpretation of "board specific",
> but I'm okay with it.

Yes, it is quite strict, but in the long term helps - people explicitly
need to enable/fill properties in new board DTSes, which hopefully will
trigger some thinking - "do I really have 385 MHz XO clock"?

Although here it might not really important, but that approach is useful
for all other cases, including aliases and buses. And one day, such
clear design will help new guys doing new hardware bring-up and they
will say: "I will start my new DTS board on some examples from mainline". :)

Best regards,
Krzysztof