linux-kernel - Re: [PATCH] arch:x86:pci:irq.c: Improve log message when IRQ cannot be identified

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Message-ID: <20220131212213.GA510910@bhelgaas>
Date:   Mon, 31 Jan 2022 15:22:13 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Brent Spillner <spillner@....org>, bhelgaas@...gle.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch:x86:pci:irq.c: Improve log message when IRQ cannot
 be identified

On Fri, Jan 28, 2022 at 01:36:53PM -0800, Dave Hansen wrote:
> On 1/28/22 12:48, Brent Spillner wrote:
> > It seems like the multiline string literal is your main pain point--- would
> > 
> > +#ifdef CONFIG_ACPI
> > +                       if (acpi_noirq)
> > +                               msg = "; consider removing acpi=noirq";
> > +                       else
> > +                               msg = "; recommend verifying UEFI/BIOS
> > IRQ options";
> > +#else
> > +                       msg = "; recommend verifying UEFI/BIOS IRQ
> > options or enabling ACPI";
> > +#endif
> > 
> > be OK without going to IS_ENABLED()?  (Personally, I think the #ifdef
> > style is more readable.)
> 
> I think that's _better_ than what was in the patch.  But, even with it,
> I still think the #ifdef mess borders on unreadable.
> 
> But, if Bjorn likes it, then go for it. :)

I was hoping to avoid commenting at all ;)

I'm a little bit averse to suggesting *any* command-line options
because users shouldn't have to use options like these.  It would be
better if we got a bug report and could fix the bug or add a quirk to
work around a firmware issue automatically.

If a user finds a command-line option that "works," the problem is
solved as far as they are concerned, but it doesn't help the next
person who trips over it.

I think pci_acpi_init() should warn when "acpi=noirq" was used because
the only reason to use it should be to work around a firmware defect,
and ideally, we could make a quirk to do that.  Maybe the doc should
suggest a bug report.

What does "verifying UEFI/BIOS IRQ options" mean?  I could go look at
the BIOS setup menu, but I would have no idea what to look for, so the
only thing I could do would be to try randomly changing IRQ-related
things.  If that happens to hit on a working configuration, I might
be happy, but it wouldn't help the next person at all.  I'd rather see
a bug report.  Then we could at least try to make a quirk so no
command line option would be needed.

Bjorn