linux-kernel - Re: [PATCH] x86/sfi: fix ioapic gsi range

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Date:	Tue, 08 Jun 2010 13:04:15 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Alan Cox <alan@...ux.intel.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Feng Tang <feng.tang@...el.com>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] x86/sfi: fix ioapic gsi range

"H. Peter Anvin" <hpa@...or.com> writes:

> On 06/08/2010 01:10 AM, Alan Cox wrote:
>>>> You may not use a 1-1 mapping if you don't have legacy irqs.  Linux
>>>> irqs 0-15 are the ISA irqs you may not use those irq numbers for
>> 
>> Linux IRQ 0 is "no IRQ assigned", except buried in certain bits of arch
>> specific historical knowledge.
>> 
>> Also calling 1-15 ISA IRQ lines is also somewhat misleading given they
>> are almost certainly routing for PCI devices. "PIC IRQ routing" maybe -
>> but even that is not really true on a lot of PC hardware today except by
>> convention.
>
> Yes, but I gather IRQ/GSI 0 is an early-acquire primary timer on MRST on
> Moorestown just as on PC/AT... just a different one.  Hence "special" in
> the same sort of way.  I don't really care, personally, though.

Right.  I have to admit I was stunned when I realized that request_irq
works and has worked for a long time with irq 0.  I think that might
actually be a bug.  setup_irq is traditionally used for irq 0.

Eric
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