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

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Date:   Mon, 20 Nov 2023 20:31:13 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     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 20/11/2023 20:18, Geert Uytterhoeven wrote:
> Hi Krzysztof,
> 
> 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...
> 
> The Renesas White-Hawk CPU board can be used standalone, and has a
> separate power input connector for this operation mode.  As it has RAM,
> Ethernet, serial console, eMMC, and even mini-DP, it can serve useful
> purposes on its own.
> I agree it's not a super-good example, as the board is not really a
> "SoM", and we currently don't have r8a779g0-white-hawk-cpu.dts, only
> r8a779g0-white-hawk-cpu.dtsi.
> 
> The RZ/A2M CPU Board is a real SoM, which can be powered over USB.
> It has less standard connectors (microSD, USB, MIPI CSI-2), but still
> sufficient features to be usable on its own.
> Again, we're doing a bad job, as we only have a DTS for the full eval
> board (r7s9210-rza2mevb.dts).
> 
> 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?

Best regards,
Krzysztof