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

Geert Uytterhoeven
2023-11-20T19:19:28Z

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...

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds