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 20:09:32 +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, Rafael J. Wysocki wrote:
> 
> > BTW, did you even to look at the code _as_ _is_ in linux-next?
> 
>  Well, I hope it has not changed too much since my recent work in this 
> area...

Please look at it.

> > In fact, it is _impossible_ that either apic1 or pin1 are equal to -1 at this
> > point, because of this part:
> 
>  With the workaround activated it is virtually certain.

Which workaround?

There are no any workarounds related to this problem in the 20080704 linux-next
and that's what my patch was against.

> > 	/*
> > 	 * 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.
> 
>  And the conclusion is?  If we leave MP-table setups aside as irrelevant
> for this configuration, we can be almost certain apic2 and pin2 are both
> equal to -1 at this point.  This is because (unlike the MP table) ACPI has
> no provisions in its tables for ExtINTA APIC interrupt inputs.  Therefore
> the only case apic2 and pin2 may not be equal -1 here is when the firmware
> had set up one of the inputs as such in the hardware before initiating
> bootstrap which has been subsequently noted by a piece of code in
> enable_IO_APIC() which examines the I/O APIC for such a condition.
> 
>  I have taken these circumstances very much into account when preparing
> the workaround, based on the assumption that if the firmware has set up an
> I/O APIC line as an ExtINTA interrupt, then it means it considers it
> suitable to use in such a manner.  This furthermore implies the line
> should be safe to be used in any valid 8259A mode of operation, such as
> one we use to forward IRQ0 transparently through the 8259A (we
> double-check it just in case though, as workarounds for hardware bugs in
> the past made it not always true).  The workaround therefore applies to
> genuine IRQ0 routing as reported by ACPI only and not any possible legacy
> ExtINTA fallback that we may attempt to use.
> 
>  Of course, as determined previously, the ExtINTA line is not safe to be
> used on your box, but it has not been set up by the firmware as an ExtINTA
> interrupt either, so the assumption mentioned above remains valid and has
> no negative impact on your system.  At this point all of apic1, apic2,
> pin1 and pin2 should be equal -1, which means the reassignments you quoted
> make no changes to the variables.
> 
> > 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).
> 
>  Which means the workaround has not triggered and the rest of cosideration 
> is therefore irrelevant.  Please get us these DMI IDs, so that we can see 
> what's wrong with the quirk.

I used those DMI IDs and your quirk didn't work, even after removing the
dependency of acpi_dmi_table[] from __i386__.  For this reason, I prepared an
alternative patch that did work and posted it for your information.

Now, you're saying that my patch couldn't work, while in fact it did.

Thanks,
Rafael
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