linux-kernel - Re: [PATCH v1 1/1] x86/platform: Increase maximum GPIO number for X86

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Date:   Mon, 16 Aug 2021 15:55:59 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v1 1/1] x86/platform: Increase maximum GPIO number for X86_64

On Mon, Aug 16, 2021 at 3:35 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Aug 16, 2021 at 03:25:13PM +0200, Rafael J. Wysocki wrote:
> > On Fri, Aug 6, 2021 at 4:44 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > > By default the 512 GPIOs is a maximum on any x86 platform.
> > > With, for example, Intel Tiger Lake-H the SoC based controller
> > > occupies up to 480 pins. This leaves only 32 available for
> > > GPIO expanders or other drivers, like PMIC. Hence, bump the
> > > maximum GPIO number to 1024 for X86_64 and leave 512 for X86_32.
>
> Thanks for review, my answers below.
>
> > > +# The GPIO number here must be sorted by descending number. In case of
> > > +# a multiplatform kernel, we just want the highest value required by the
> > > +# selected platforms.
> > > +config ARCH_NR_GPIO
> > > +       int
> > > +       default 1024 if X86_64
> > > +       default 512 if X86_32
> > > +       default 0
> >
> > Wouldn't
> >
> > default 1024 if X86_64
> > default 512
> >
> > be sufficient?
> >
> > It's either X86_64 or X86_32 anyway AFAICS.
>
> I guess so.
>
> > > +       help
> > > +         Maximum number of GPIOs in the system.
> > > +
> > > +         If unsure, leave the default value.
>
> Btw, what do you think. do we need comment above and help text here? I copied
> these from ARM, but I'm not sure it would be useful on x86 as much.

Both the comment and the help text aren't particularly useful IMO.

The comment is a bit confusing even, because x86 kernels are
multiplatform as a rule.