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

[Geert Uytterhoeven]

On Wed, Nov 22, 2023 at 9:21 AM Krzysztof Kozlowski
<krzysztof.kozlowski at linaro.org> wrote:
> On 22/11/2023 09:09, Chen-Yu Tsai wrote:
> > On Wed, Nov 22, 2023 at 4:05 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski at linaro.org> wrote:
> >> On 21/11/2023 14:50, Rafał Miłecki wrote:
> >>>> +Order of Nodes
> >>>> +--------------
> >>>> +
> >>>> +1. Nodes within any bus, thus using unit addresses for children, shall be
> >>>> +   ordered incrementally by unit address.
> >>>> +   Alternatively for some sub-architectures, nodes of the same type can be
> >>>> +   grouped together (e.g. all I2C controllers one after another even if this
> >>>> +   breaks unit address ordering).
> >>>> +
> >>>> +2. Nodes without unit addresses should be ordered alpha-numerically by the node
> >>>> +   name.  For a few types of nodes, they can be ordered by the main property
> >>>> +   (e.g. pin configuration states ordered by value of "pins" property).
> >>>> +
> >>>> +3. When extending nodes in the board DTS via &label, the entries should be
> >>>> +   ordered alpha-numerically.
> >>>
> >>> Just an idea. Would that make (more) sense to make &label-like entries
> >>> match order of nodes in included .dts(i)?
> >>>
> >>> Adventages:
> >>> 1. We keep unit address incremental order that is unlikely to change
> >>>
> >>> Disadventages:
> >>> 1. More difficult to verify
> >>
> >> Rob also proposed this and I believe above disadvantage here is crucial.
> >> If you add new SoC with board DTS you are fine. But if you add only new
> >> board, the order of entries look random in the diff hunk. Reviewer must
> >> open SoC DTSI to be able to review the patch with board DTS.
> >>
> >> If review is tricky and we do not have tool to perform it automatically,
> >> I am sure submissions will have disordered board DTS.
> >>
> >>>
> >>>
> >>>> +Example::
> >>>> +
> >>>> +    // SoC DTSI
> >>>> +
> >>>> +    / {
> >>>> +            cpus {
> >>>> +                    // ...
> >>>> +            };
> >>>> +
> >>>> +            psci {
> >>>> +                    // ...
> >>>> +            };
> >>>> +
> >>>> +            soc@ {
> >>>> +                    dma: dma-controller at 10000 {
> >>>> +                            // ...
> >>>> +                    };
> >>>> +
> >>>> +                    clk: clock-controller at 80000 {
> >>>> +                            // ...
> >>>> +                    };
> >>>> +            };
> >>>> +    };
> >>>> +
> >>>> +    // Board DTS
> >>>> +
> >>>> +    &clk {
> >>>> +            // ...
> >>>> +    };
> >>>> +
> >>>> +    &dma {
> >>>> +            // ...
> >>>> +    };
> >>>> +
> >>>> +
> >>>> +Order of Properties in Device Node
> >>>> +----------------------------------
> >>>> +
> >>>> +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
> >>>> +
> >>>> +The "status" property is by default "okay", thus it can be omitted.
> >>>
> >>> I think it would really help to include position of #address-cells and
> >>> #size-cells here. In some files I saw them above "compatible" that seems
> >>> unintuitive. Some prefer putting them at end which I think makes sense
> >>> as they affect children nodes.
> >>>
> >>> Whatever you choose it'd be just nice to have things consistent.
> >>
> >> This is a standard/common property, thus it goes to (4) above.
> >
> > It's probably a mix, but AFAIK a lot of the device trees in tree have
> > #*-cells after "status". In some cases they are added in the board
> > .dts files, not the chip/module .dtsi files.
>
> Existing DTS is not a good example :)
>
> >
> > +1 that it makes sense at the end as they affect child nodes.
>
> I still insist that status must be the last, because:
> 1. Many SoC nodes have address/size cells but do not have any children
> (I2C, SPI), so we put useless information at the end.
> 2. Status should be the final information to say whether the node is
> ready or is not. I read the node, check properties and then look at the end:
> a. Lack of status means it is ready.
> b. status=disabled means device still needs board resources/customization

+1 for status at the end (before children), so it's easy to find.
Also, reality can look like the example in the bindings, with an optional
status property appended.

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