linux-kernel - Re: [PATCH v5 04/11] dt-bindings: iio: adc: add AXP803 ADC bindings

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Date:   Wed, 31 Oct 2018 10:29:59 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     jic23@...23.retrosnub.co.uk
Cc:     Rob Herring <robh@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-iio@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Sebastian Reichel <sre@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>,
        devicetree <devicetree@...r.kernel.org>, oskari@...mela.net,
        linux-gpio@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Lee Jones <lee.jones@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Quentin Schulz <quentin.schulz@...tlin.com>
Subject: Re: [PATCH v5 04/11] dt-bindings: iio: adc: add AXP803 ADC bindings

On Mon, Oct 29, 2018 at 9:10 PM Quentin Schulz
<quentin.schulz@...tlin.com> wrote:
>
> Hi Jonathan,
>
> On Sun, Oct 28, 2018 at 03:40:11PM +0000, Jonathan Cameron wrote:
> > On Wed, 24 Oct 2018 08:56:33 -0500
> > Rob Herring <robh@...nel.org> wrote:
> >
> > > On Tue, 23 Oct 2018 21:53:23 +0300, Oskari Lemmela wrote:
> > > > The AXP803 ADC is compatible with AXP813 ADC, but add
> > > > specific compatible for it.
> > > >
> > > > Signed-off-by: Oskari Lemmela <oskari@...mela.net>
> > > > ---
> > > >  Documentation/devicetree/bindings/iio/adc/axp20x_adc.txt | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > >
> > > Reviewed-by: Rob Herring <robh@...nel.org>
> >
> > This doesn't seem to have any dependencies with the other patches
> > so applied to the togreg branch of iio.git and pushed out as testing
> > for the autobuilders to ignore.  However I am a little curious to know
> > why we would add the ID and then not use it (that I can see)?
> >
>
> Sometimes with Allwinner (and X-Powers), two IPs seem identical until we
> discover something that is slightly different. When this happens, we
> have to add a compatible to differentiate both. However, we would also
> need to change the Device Tree to change the compatible. We would need
> to handle the driver behaviour for both Device Trees.
>
> So better anticipate a possible difference so that we don't have to do
> some hacks in the driver to handle the device correctly.
>
> As always, Chen-Yu or Maxime may know better so I'm just stating what I
> seem to recall.

With Allwinner stuff (X-Powers included), sometimes the documents are
incomplete or have errors. We tend to add a model-specific compatible
just in case things turn out not to be so compatible, unless someone
has triple-checked everything, documents and actual hardware included.

However we don't actually document these, so this patch isn't strictly
needed. (I suppose this might annoy the device tree binding maintainers.)

ChenYu