[PATCH v3] docs: dt-bindings: add DTS Coding Style document

[Geert Uytterhoeven]

Hi Francesco,

On Wed, Nov 29, 2023 at 8:29 AM Francesco Dolcini <francesco at dolcini.it> wrote:
> On Sat, Nov 25, 2023 at 07:44:22PM +0100, Krzysztof Kozlowski wrote:
> > Document preferred coding style for Devicetree sources (DTS and DTSI),
> > to bring consistency among all (sub)architectures and ease in reviews.
>
> Thank Krzysztof, we had most of this collected as BKM in some internal
> documents and it's great to see the effort to consolidate this and add
> it to the kernel documentation.
>
> > ---
> > +Following order of properties in device nodes is preferred:
> > +
> > +1. compatible
> > +2. reg
> > +3. ranges
> > +4. Standard/common properties (defined by common bindings, e.g. without
> > +   vendor-prefixes)
> > +5. Vendor-specific properties
> > +6. status (if applicable)
> > +7. Child nodes, where each node is preceded with a blank line
>
> On point 4, do you have a more explicit way to define what is an actual
> standard/common property? You mention the vendor-prefixes as an example,
> is this just an example or this is the whole definition?

I think there are three classes of standard properties:
  1. Device Tree Specification (from devicetree.org)
  2. dt-schema
  3. Common subsystem bindings (Documentation/devicetree/bindings/)
     (may be moved to 2).

> What would be the order for this for example (from an existing DTS file)?
>
>         reg_sdhc1_vmmc: regulator-sdhci1 {
>                 compatible = "regulator-fixed";
>                 pinctrl-names = "default";
>                 pinctrl-0 = <&pinctrl_sd1_pwr_en>;
>                 enable-active-high;
>                 gpio = <&main_gpio0 29 GPIO_ACTIVE_HIGH>;
>                 off-on-delay-us = <100000>;
>                 regulator-max-microvolt = <3300000>;
>                 regulator-min-microvolt = <3300000>;
>                 regulator-name = "+V3.3_SD";
>                 startup-delay-us = <2000>;
>         };
>
> I guess the point that is not obvious to me here is where do we want
> pinctrl. I like it at position between 3 and 4, the rationale is that is
> a very frequent property and this way it will be in a similar place for
> every node.

The pinctrl properties are only present in board DTS files, not in
SoC DTSi files.  There are two classes of them:
  1. Extension of on-SoC devices, where they are added to already
     existing nodes, defined in the SoC DTSi files, e.g. (from the same
     existing DTS file):

         &cpsw3g {
                 pinctrl-names = "default";
                 pinctrl-0 = <&pinctrl_rgmii1>;
                 status = "disabled";
         };

  2. Pure board devices, in new nodes (e.g. your regulator example).
     These are less common, so I don't even know from the top of my
     mind when I last added one, and where ;-)
     I'd guess after all standard properties?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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