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Date:   Tue, 6 Sep 2022 16:53:03 +0300
From:   Andy Shevchenko <andriy.shevchenko@intel.com>
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Martyn Welch <martyn.welch@collabora.co.uk>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Martyn Welch <martyn.welch@collabora.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/5] dt-bindings: gpio: pca95xx: add entry for
 pcal6534 and PI4IOE5V6534Q
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On Tue, Sep 06, 2022 at 03:33:34PM +0200, Linus Walleij wrote:
> On Tue, Sep 6, 2022 at 3:20 PM Andy Shevchenko
> <andriy.shevchenko@intel.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@intel.com> wrote:
> > > > On Tue, Sep 06, 2022 at 09:28:16AM +0100, Martyn Welch wrote:

...

> > > > > +    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.

This makes a lot of sense, thank you for explaining this. Indeed, now I
understand the absence of Diodes in the code.

> > 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
> (ML stands for Meta Language).
> 
> All meta languages are mysterious.

Yeah :-)

-- 
With Best Regards,
Andy Shevchenko