linux-kernel - Re: [PATCH v2 2/5] dt-bindings: gpio: pca95xx: add entry for pcal6534 and PI4IOE5V6534Q

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Date:   Tue, 6 Sep 2022 09:19:52 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...el.com>,
        Martyn Welch <martyn.welch@...labora.co.uk>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Martyn Welch <martyn.welch@...labora.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] dt-bindings: gpio: pca95xx: add entry for pcal6534
 and PI4IOE5V6534Q

On Tue, Sep 6, 2022 at 8:33 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Tue, Sep 6, 2022 at 3:20 PM Andy Shevchenko
> <andriy.shevchenko@...el.com> wrote:
> > On Tue, Sep 06, 2022 at 03:08:00PM +0200, Linus Walleij wrote:
> > > On Tue, Sep 6, 2022 at 2:19 PM Andy Shevchenko
> > > <andriy.shevchenko@...el.com> wrote:
> > > > On Tue, Sep 06, 2022 at 09:28:16AM +0100, Martyn Welch wrote:
> > > > > From: Martyn Welch <martyn.welch@...labora.com>
> > > > >
> > > > > The NXP PCAL6534 is a 34-bit I2C I/O expander similar to the PCAL6524. The
> > > > > Diodes PI4IOE5V6534Q is a functionally identical chip provided by Diodes
> > > > > Inc.
> > > >
> > > > ...
> > > >
> > > > > +    oneOf:
> > > > > +      - items:
> > > > > +        - const: diodes,pi4ioe5v6534q
> > > > > +        - const: nxp,pcal6534
> > > >
> > > > ^^^
> > > >
> > > > > +      - items:
> > > > > +        - enum:
> > > >
> > > > > +          - nxp,pcal6534
> > > >
> > > > ^^^
> > > >
> > > > Not sure why is this dup?
> > >
> > > No that is how DT compatibles work. One version of the component,
> > > bought from NXP will look like this:
> > >
> > > compatible = "nxp,pcal6534";
> > >
> > > Another version bought from diodes will look like this:
> > >
> > > compatible = "diodes,pi4ioe5v6534q", "nxp,pcal6534";
> > >
> > > Then the drivers are probed matching from left to right,
> > > with the "most compatible" matching first.
> > >
> > > This also answers your question on the implementation.
> >
> > Then I don't understand why the const list above is only for new chips
> > and not for the old one where the same can be applied.
>
> That's YAML. It's because the const list is the most compact way
> to express two precise items following after each other, and the enum
> list is an implicit list of single-item const:s, as you cannot enum
> tuples.
>
> > Mysterious ways of DT...
>
> It's not DT, it's YAML that is mysterious. DT itself is a pretty
> straight-forward
> grammar, while YAML is a meta-grammar describing the DT grammar

Not YAML, but json-schema is the grammar. YAML is just the file format
and it's a JSON compatible subset of YAML (no anchors, refs, tags).

> (ML stands for Meta Language).

Huh? yaml.org says: YAML Ain't Markup Language™

Rob