linux-kernel - Re: [PATCH 2/2] acpi: Disable IRQ 0 through I/O APIC for some HP systems

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Date:	Mon, 7 Jul 2008 14:28:52 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <lenb@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-next@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 2/2] acpi: Disable IRQ 0 through I/O APIC for some HP systems

On Monday, 7 of July 2008, Maciej W. Rozycki wrote:
> On Mon, 7 Jul 2008, Ingo Molnar wrote:
> 
> > > Please note two things:
> > > (1) The whole acpi_dmi_table[] thing originally depended on __i386__, so it
> > >     wouldn't work on x86-64 no matter what.  I removed that dependecy, but
> > >     I have no idea why it was there and so I'm not sure if that's correct. 
> 
>  Well spottedd -- perhaps the x86-64 was though to be perfect. ;)
> 
> > > (2) The clear_IO_APIC_pin(apic1, pin1) done if 
> > >     disable_irq0_through_ioapic is true is absolutely essential.  The 
> > >     symptoms are 100% reproducible without it.
> > 
> > thanks, applied to tip/x86, to give this some more testing.
> > 
> > the clear_IO_APIC_pin() is the most worrisome aspect of the change - but 
> > since we are already in limited quirk mode, does it hurt? Maciej, any 
> > preferences?
> 
>  It makes absolutely no sense and should be harmful to call
> clear_IO_APIC_pin(apic1, pin1) here, because both apic1 and pin1 should be
> equal to -1 here.  If it has to be called, then I suppose the DMI matching 
> did not work and the workaround has not been enabled.

BTW, did you even to look at the code _as_ _is_ in linux-next?

In fact, it is _impossible_ that either apic1 or pin1 are equal to -1 at this
point, because of this part:

	/*
	 * Some BIOS writers are clueless and report the ExtINTA
	 * I/O APIC input from the cascaded 8259A as the timer
	 * interrupt input.  So just in case, if only one pin
	 * was found above, try it both directly and through the
	 * 8259A.
	 */
	if (pin1 == -1) {
		pin1 = pin2;
		apic1 = apic2;
		no_pin1 = 1;
	} else if (pin2 == -1) {
		pin2 = pin1;
		apic2 = apic1;
	}

that originates from your patch.

End even without this part apic1 and pin1 are _not_ equal to -1 on this box
(apic2 and pin2 are, but that's a different matter).

Thanks,
Rafael
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