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

Krzysztof Kozlowski
2023-11-20T19:31:54Z

On 20/11/2023 20:18, Geert Uytterhoeven wrote:
> Hi Krzysztof,
>
> On Mon, Nov 20, 2023 at 3:53 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.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