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

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Message-ID: <CAMuHMdWm-gRPHeHyuX3_eR+9chJEw3iiZwCNBnoiRPHzoMAs6w@mail.gmail.com>
Date:   Wed, 22 Nov 2023 09:53:15 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Michal Simek <michal.simek@....com>
Cc:     Dragan Simic <dsimic@...jaro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        wens@...nel.org,
        Rafał Miłecki <zajec5@...il.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>,
        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

Hi Michal,

On Wed, Nov 22, 2023 at 9:50 AM Michal Simek <michal.simek@....com> wrote:
> On 11/22/23 09:29, Dragan Simic wrote:
> > On 2023-11-22 09:21, Krzysztof Kozlowski wrote:
> >> On 22/11/2023 09:09, Chen-Yu Tsai wrote:
> >>> On Wed, Nov 22, 2023 at 4:05 PM Krzysztof Kozlowski
> >>> <krzysztof.kozlowski@...aro.org> wrote:
> >>>>
> >>>> On 21/11/2023 14:50, Rafał Miłecki wrote:
> >>>>>> +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
> >
> > I agree with the "status" belonging to the very end, because it's both logical
> > and much more readable.  Also, "status" is expected to be modified in the
> > dependent DT files, which makes it kind of volatile and even more deserving to
> > be placed last.
>
> I am just curious if having status property at the end won't affect
> execution/boot up time. Not sure how it is done in Linux but in U-Boot at least
> (we want to have DTs in sync between Linux and U-Boot) of_find_property is
> pretty much big loop over all properties. And status property defined at the end
> means going over all of them to find it out to if device is present.
> Not sure if Linux works in the same way but at least of_get_property is done in
> the same way.

As the default is "okay", you have to loop over all properties anyway.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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