linux-kernel - Re: [PATCH] irqchip/renesas-irqc: Use platform_get_irq

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Date:   Mon, 27 Dec 2021 13:04:19 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip/renesas-irqc: Use platform_get_irq_optional() to
 get the interrupt

On Mon, Dec 27, 2021 at 12:58 PM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Mon, Dec 27, 2021 at 11:49 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Mon, Dec 27, 2021 at 12:24 PM Geert Uytterhoeven
> > <geert@...ux-m68k.org> wrote:
> > > On Mon, Dec 27, 2021 at 11:10 AM Andy Shevchenko
> > > <andy.shevchenko@...il.com> wrote:
> > > > On Mon, Dec 27, 2021 at 12:02 PM Geert Uytterhoeven
> > > > <geert@...ux-m68k.org> wrote:
> > > > > On Mon, Dec 27, 2021 at 10:57 AM Andy Shevchenko
> > > > > <andy.shevchenko@...il.com> wrote:
> > > > > > On Mon, Dec 27, 2021 at 11:45 AM Geert Uytterhoeven
> > > > > > <geert@...ux-m68k.org> wrote:
> > > > > > > On Sun, Dec 26, 2021 at 9:49 AM Andy Shevchenko
> > > > > > > <andy.shevchenko@...il.com> wrote:
> > > > > > > > On Sun, Dec 26, 2021 at 1:59 AM Lad, Prabhakar
> > > > > > > > <prabhakar.csengg@...il.com> wrote:
> > > > > > > > > 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.
> > > >
> > > > Forgot to comment on this, then why is it a problem to allow
> > > > platfiorm_get_irq_optional() use 0 for no IRQ?
> > > > So, it seems you gave me a good justification for my way :-)
> > >
> > > In se that is not a problem, assumed by now everybody should have
> > > seen the warning, right?  Unfortunately that assumption is probably
> > > not true, as people may not upgrade their kernel, cfr. my SH Ethernet
> > > example.
> > >
> > > Apart from that, any new conversion to platfiorm_get_irq_optional()
> > > might cause a regression on an obscure platform still using IRQ0.
> >
> > What architectures?
> > Are there any examples besides ethernet drivers on SH?
>
> Sorry, I don't know.
>
> > Let's start  a list:
> > SH: only few cases related to smc911 Ethernet driver
>
> Time to get rid of SH ;-)
>
> > x86: Legacy APIC 1:1 mapping, where 0 is used by timer which doesn't
> > involve platform API
>
> Time to get rid of x86 ;-)

Why (in both cases)? I have mentioned that x86 doesn't use vIRQ0 via
platform APIs, SH can be fixed, if you are interested in fixing, of
course, by switching to IRQ domains.

> > ...???...
> >
> > And what about "getting IRQ without big warning"? What did you have in
> > mind when you put it?
>
> If the driver uses platform_get_resource(..., IORESOURCE_IRQ, ...) to
> get the IRQ number, the warning in platform_get_irq_optional()
> doesn't trigger, as the latter is not called?

So, again, let's put the comment to those drivers then and avoid
obfuscation of the rest of the kernel, would it be feasible?

-- 
With Best Regards,
Andy Shevchenko