linux-kernel - Re: [PATCH] of: property: do not create device links from *nr-gpios

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Date:   Mon, 5 Apr 2021 13:18:56 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] of: property: do not create device links from *nr-gpios

On Mon, Apr 5, 2021 at 1:10 PM Ilya Lipnitskiy
<ilya.lipnitskiy@...il.com> wrote:
>
> Hi Saravana,
>
> On Mon, Apr 5, 2021 at 1:01 PM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > On Sun, Apr 4, 2021 at 8:14 PM Ilya Lipnitskiy
> > <ilya.lipnitskiy@...il.com> wrote:
> > >
> > > [<vendor>,]nr-gpios property is used by some GPIO drivers[0] to indicate
> > > the number of GPIOs present on a system, not define a GPIO. nr-gpios is
> > > not configured by #gpio-cells and can't be parsed along with other
> > > "*-gpios" properties.
> > >
> > > scripts/dtc/checks.c also has a special case for nr-gpio{s}. However,
> > > nr-gpio is not really special, so we only need to fix nr-gpios suffix
> > > here.
> >
> > The only example of this that I see is "snps,nr-gpios".
> arch/arm64/boot/dts/apm/apm-shadowcat.dtsi uses "apm,nr-gpios", with
> parsing code in drivers/gpio/gpio-xgene-sb.c. There is also code in
> drivers/gpio/gpio-adnp.c and drivers/gpio/gpio-mockup.c using
> "nr-gpios" without any vendor prefix.

Ah ok. I just grepped the DT files. I'm not sure what Rob's position
is on supporting DT files not in upstream. Thanks for the
clarification.

> I personally don't think causing regressions is good for any reason,

I agree, but this is not a functional regression. Just a warning
that's spit out. I don't have a strong opinion on the stack dump vs
not, but I think we should at least reject future additions like this
and limit the exceptions to exactly what's allowed today. nr-gpios
(without any vendor prefix) is especially annoying to me.

Looks like even the DT spec has an exception only for vendor,nr and not just nr.
https://github.com/devicetree-org/dt-schema/blob/master/schemas/gpio/gpio-consumer.yaml#L20

-Saravana

> so I think we need to fix this in stable releases. The patch can be
> reverted when nr-gpios is no longer special. The logic here should
> also be aligned with scripts/dtc/checks.c, I actually submitted a
> patch to warn about "nr-gpios" only and not "nr-gpio" in dtc as well:
> https://www.spinics.net/lists/devicetree-compiler/msg03619.html
>
> Ilya