linux-kernel - Re: [PATCH v2] docs: dt-bindings: add DTS Coding Style document

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Date:   Tue, 21 Nov 2023 11:28:29 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Michal Simek <michal.simek@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, Andrew Davis <afd@...com>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <andersson@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Heiko Stuebner <heiko@...ech.de>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Nishanth Menon <nm@...com>, Olof Johansson <olof@...om.net>,
        linux-rockchip@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org,
        linux-amlogic@...ts.infradead.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2] docs: dt-bindings: add DTS Coding Style document

On 21/11/2023 11:13, Dmitry Baryshkov wrote:
> On Tue, 21 Nov 2023 at 10:09, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>
>> Hi Krzysztof,
>>
>> On Tue, Nov 21, 2023 at 8:47 AM Krzysztof Kozlowski
>> <krzysztof.kozlowski@...aro.org> wrote:
>>> On 21/11/2023 08:33, Michal Simek wrote:
>>>> On 11/20/23 20:31, Krzysztof Kozlowski wrote:
>>>>> On 20/11/2023 20:18, Geert Uytterhoeven wrote:
>>>>>> On Mon, Nov 20, 2023 at 3:53 PM Krzysztof Kozlowski
>>>>>> <krzysztof.kozlowski@...aro.org> wrote:
>>>>>>> On 20/11/2023 15:01, Michal Simek wrote:> >
>>>>>>>> On 11/20/23 09:40, Krzysztof Kozlowski wrote:
>>>>>>>>> Document preferred coding style for Devicetree sources (DTS and DTSI),
>>>>>>>>> to bring consistency among all (sub)architectures and ease in reviews.
>>>>>>
>>>>>>>>> +Organizing DTSI and DTS
>>>>>>>>> +-----------------------
>>>>>>>>> +
>>>>>>>>> +The DTSI and DTS files should be organized in a way representing the common
>>>>>>>>> +(and re-usable) parts of the hardware.  Typically this means organizing DTSI
>>>>>>>>> +and DTS files into several files:
>>>>>>>>> +
>>>>>>>>> +1. DTSI with contents of the entire SoC (without nodes for hardware not present
>>>>>>>>> +   on the SoC).
>>>>>>>>> +2. If applicable: DTSI with common or re-usable parts of the hardware (e.g.
>>>>>>>>> +   entire System-on-Module).
>>>>>>>>
>>>>>>>> DTS/DTSI - SOMs can actually run as they are that's why it is fair to say that
>>>>>>>> there doesn't need to be DTS representing the board.
>>>>>>>
>>>>>>> I have never seen a SoM which can run without elaborate hardware-hacking
>>>>>>> (e.g. connecting multiple wires to the SoM pins). The definition of the
>>>>>>> SoM is that it is a module. Module can be re-used, just like SoC.
>>>>>>
>>>>>> /me looks at his board farm...
>>
>>>>>> I guess there are (many) other examples...
>>>>>
>>>>> OK, I never had such in my hands. Anyway, the SoM which can run
>>>>> standalone  has a meaning of a board, so how exactly you want to
>>>>> rephrase the paragraph?
>>>>
>>>> What about?
>>>>
>>>> 2. If applicable: DTSI with common or re-usable parts of the hardware (e.g.
>>>> entire System-on-Module). DTS if runs standalone.
>>>
>>> OK, but then it's duplicating the option 3. It also suggests that SoM
>>> should be a DTS, which is not what we want for such case. Such SoMs must
>>> have DTSI+DTS.
>>
>> So you want us to have a one-line <SoM>.dts, which just includes <SoM>.dtsi?
> 
> Well, I think it is impossible to run SoM directly. There is a carrier
> board anyway, which includes at least regulators. So, I guess, the
> SoM.dts will not be a oneline file.

Geert claims he has SoM with an USB connector which can run when power
is supplied by that USB connector. I can imagine a CPU board (so a SoM
in format of a board, not small DIMM-card) which has connectors e.g. for
power and a slot for external motherboard for additional, optional
interfaces.

Look at picture on 14th page:
https://www.renesas.com/us/en/document/mat/rza2m-cpu-board-users-manual

This looks like some case of SoM, although maybe not that popular
outside of Renesas :)

Best regards,
Krzysztof