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Date:   Tue, 6 Sep 2022 16:19:57 +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 03:08:00PM +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:
> > > From: Martyn Welch <martyn.welch@collabora.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.

Mysterious ways of DT...

-- 
With Best Regards,
Andy Shevchenko