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

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Message-ID: <20210406174050.GA1963300@robh.at.kernel.org>
Date:   Tue, 6 Apr 2021 12:40:50 -0500
From:   Rob Herring <robh@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>,
        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 05, 2021 at 01:18:56PM -0700, Saravana Kannan wrote:
> 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.

If it's something we had documented, then we have to support it (also 
conditioned on someone noticing). I'm hoping we can just delete APM and 
other defunct ARM server DTs soon, but we could update them to use 
'ngpios' instead.

gpio-mockup doesn't have a binding, so no DT ABI. Hard to tell if 
gpio-adnp.c has any users.

Rob