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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 27 Dec 2021 11:19:29 +0100
Message-ID: <CAMuHMdU+PpVM=_+og0pr8T_O6Dh7gRfA9i-77qKsuJpxzg1SvA@mail.gmail.com>
Subject: Re: [PATCH] irqchip/renesas-irqc: Use platform_get_irq_optional() to
 get the interrupt
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@gmail.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Precedence: bulk

Hi Andy,

On Mon, Dec 27, 2021 at 11:06 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Mon, Dec 27, 2021 at 12:02 PM Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
> > On Mon, Dec 27, 2021 at 10:57 AM Andy Shevchenko
> > <andy.shevchenko@gmail.com> wrote:
> > > On Mon, Dec 27, 2021 at 11:45 AM Geert Uytterhoeven
> > > <geert@linux-m68k.org> wrote:
> > > > On Sun, Dec 26, 2021 at 9:49 AM Andy Shevchenko
> > > > <andy.shevchenko@gmail.com> wrote:
> > > > > On Sun, Dec 26, 2021 at 1:59 AM Lad, Prabhakar
> > > > > <prabhakar.csengg@gmail.com> wrote:
> > > > > > On Sat, Dec 25, 2021 at 5:40 PM Andy Shevchenko
> > > > > > <andy.shevchenko@gmail.com> wrote:
> > > > > > > On Sat, Dec 25, 2021 at 7:28 PM Lad, Prabhakar
> > > > > > > <prabhakar.csengg@gmail.com> wrote:
> > > > > > > > On Sat, Dec 25, 2021 at 4:46 PM Andy Shevchenko
> > > > > > > > <andy.shevchenko@gmail.com> wrote:
> > > > > > > > > On Thu, Dec 16, 2021 at 9:52 AM Lad Prabhakar
> > > > > > > > > <prabhakar.mahadev-lad.rj@bp.renesas.com> wrote:
> > > > > > >
> > > > > > > > > ret = platform_get_irq_optional(...);
> > > > > > > > > if (ret < 0 && ret != -ENXIO)
> > > > > > > > >   return ret;
> > > > > > > > > if (ret > 0)
> > > > > > > > >   ...we got it...
> > > > > > > > >
> > > > > > > > > It will allow the future API fix of platform_get_irq_optional() to be
> > > > > > > > > really optional.
> > > > > > > > >
> > > > > > > > Later patch [0] (merged into -next) does check for -ENXIO first.
> > > > > > > >
> > > > > > > > [0] https://lore.kernel.org/lkml/20211216182121.5323-1-prabhakar.mahadev-lad.rj@bp.renesas.com/t/
> > > > > > >
> > > > > > > The problem is that it doesn't consider 0 as no IRQ.
> > > > > > >
> > > > > > Can you please point me to the discussion/patch where this API change
> > > > > > is considered/discussed. Just to clarify now the new API for
> > > > > > platform_get_irq_optional() will return "0" in case there is no
> > > > > > interrupt and not not -ENXIO anymore?
> > > > >
> > > > > The longest one happened here:
> > > > > https://lore.kernel.org/linux-ide/20211209145937.77719-1-andriy.shevchenko@linux.intel.com/T/#u
> > > > >
> > > > > It has links to some other discussions on the topic.
> > > > >
> > > > > > When will this patch be merged for the new api, so that I can base my
> > > > > > patches on top of it to avoid more changes?
> > > > >
> > > > > You can simply imply that, I dunno when it gets merged (from my point
> > > > > of view the users should be fixed first, and since you are adding
> > > > > users, the burden is increasing).
> > > >
> > > > Not only users (drivers), but also providers (architecture-specific code).
> > > > IRQ zero is still valid on some architectures, e.g. on SH[1].
> > >
> > > Are we talking about vIRQ?
> > > And users are fine with a big warning?
> >
> > The warning is only seen when a driver uses platorm_get_irq{,_optional}().
> > There are several other ways to obtain interrupts, avoiding the
> > big warning.
> >
> > > My understanding is that the architecture code there is broken. It
> > > needs to be fixed to use IRQ domains and all that machinery instead of
> > > what it does.
> > >
> > > 0 is "no IRQ" in Linux.
> > >
> > > > [1] https://lore.kernel.org/linux-renesas-soc/CAMuHMdUg3=q7gyaVHP0XcYUOo3PQUUv8Hc8wp5faVQ+bTBpg4A@mail.gmail.com/
> >
> > BTW, perhaps the IRQ subsystem should switch from integer IRQ numbers
> > to an opaque object, like was done for GPIO before?
>
> Hasn't it been done a long time ago?
> IIRC somewhere in ~2014 timeframe.
>
> > The IRQ subsystem
> > is one of the few (only?) subsystems still using plain integers.
>
> It uses opaque objects for which the plain integer is a unique key.

And the key "cannot" be zero.

"cannot": that was the end goal, which is AFAIK still not reached, as we
still have IRQ zero is struct resource in platform files.

>
> > That
> > way we don't need this two-step platform_get_irq_optional() conversion
> > (step 1: check for both -ENXIO and zero, step 2: drop the check for
> > -ENXIO).

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