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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 4 Jan 2022 10:47:21 +0100
Message-ID: <CAMuHMdWjGUHZQhKDPASfpfNOiUg9HP2f3DsUsmJoijap29xpyQ@mail.gmail.com>
Subject: Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq() and
 its ilk
To:     Marc Zyngier <maz@kernel.org>
Cc:     Sergey Shtylyov <s.shtylyov@omp.ru>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
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On Tue, Jan 4, 2022 at 10:26 AM Marc Zyngier <maz@kernel.org> wrote:
> [Adding Geert]
>
> On Sat, 06 Nov 2021 20:26:47 +0000,
> Sergey Shtylyov <s.shtylyov@omp.ru> wrote:
> > The commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is
> > invalid") only calls WARN() when IRQ0 is about to be returned, however
> > using IRQ0 is considered invalid (according to Linus) outside the arch/
> > code where it's used by the i8253 drivers. Many driver subsystems treat
> > 0 specially (e.g. as an indication of the polling mode by libata), so
> > the users of platform_get_irq[_byname]() in them would have to filter
> > out IRQ0 explicitly and this (quite obviously) doesn't scale...
> > Let's finally get this straight and return -EINVAL instead of IRQ0!
> >
> > Fixes: a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> > Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>

> > --- driver-core.orig/drivers/base/platform.c
> > +++ driver-core/drivers/base/platform.c
> > @@ -231,7 +231,8 @@ int platform_get_irq_optional(struct pla
> >  out_not_found:
> >       ret = -ENXIO;
> >  out:
> > -     WARN(ret == 0, "0 is an invalid IRQ number\n");
> > +     if (WARN(!ret, "0 is an invalid IRQ number\n"))
> > +             return -EINVAL;
> >       return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(platform_get_irq_optional);
> > @@ -445,7 +446,8 @@ static int __platform_get_irq_byname(str
> >
> >       r = platform_get_resource_byname(dev, IORESOURCE_IRQ, name);
> >       if (r) {
> > -             WARN(r->start == 0, "0 is an invalid IRQ number\n");
> > +             if (WARN(!r->start, "0 is an invalid IRQ number\n"))
> > +                     return -EINVAL;
> >               return r->start;
> >       }
>
> Geert recently mentioned that a few architectures (such as sh?) still
> use IRQ0 as something valid in limited cases.

https://lore.kernel.org/all/CAMuHMdUg3=q7gyaVHP0XcYUOo3PQUUv8Hc8wp5faVQ+bTBpg4A@mail.gmail.com

TL;DR: Probably only smsc911x Ethernet on the AP-SH4A-3A and
AP-SH4AD-0A boards, which should trigger the warning since v5.8.

> From my PoV, this patch is fine, but please be prepared to fix things
> in a couple of years when someone decides to boot a recent kernel on
> their pet dinosaur. With that in mind:
>
> Acked-by: Marc Zyngier <maz@kernel.org>

TBH, I don't see much point in this patch, as the WARN() has been
there since a while, and the end goal is to return zero instead of
-ENXIO for no interrupt, right?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds