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

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Date:   Tue, 6 Apr 2021 14:28:00 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Cc:     Rob Herring <robh@...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 Tue, Apr 6, 2021 at 12:28 PM Ilya Lipnitskiy
<ilya.lipnitskiy@...il.com> wrote:
>
> On Tue, Apr 6, 2021 at 10:40 AM Rob Herring <robh@...nel.org> wrote:
> >
> > 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
> Do I read this correctly as a sort-of Ack of my proposed [PATCH v2] in
> this thread, since it aligns the code with the published DT schema?

He's talking about the DT binding documentation in the kernel.

I interpret Rob's reply as, you can do all of this:
1. Just fix up all drivers that use "*nr-gpios" that don't have
binding documentation in the kernel. Change them to use ngpios.
2. Try to switch away old defunct ARM server DTs from nr-gpios to
ngpios (both drivers and DT) and see if people notice.
3. Change the fw_devlink parsing code to have exceptions only for
cases that are using nr-gpios after (1) and (2).

-Saravana