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

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Date:   Mon, 5 Apr 2021 13:10:47 -0700
From:   Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
To:     Saravana Kannan <saravanak@...gle.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

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.

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