linux-kernel - Re: [PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs

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Date:	Fri, 26 Aug 2011 09:24:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Cyrill Gorcunov <gorcunov@...il.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Ralf Jung <ralfjung-e@....de>,
	Yinghai Lu <yinghai@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86, ioapic: Reserve only 128 bytes for IOAPICs

On 08/26/2011 09:21 AM, Bjorn Helgaas wrote:
> 
> Is there some spec that requires all IOAPICs to be 1K aligned?  I
> don't doubt that's the case; I'd just like to see something more
> concrete than folklore.  I'm pretty sure there's some (possibly
> secret) "IOAPIC architecture spec," and a section reference to it
> would be nice.  Even before my patch, I don't think we actually
> checked or enforced any *alignment* -- we only set the size.  I don't
> know if it's worth it unless we have a problem it would fix, and it's
> conceivable that we'd start warning about a perfectly functional
> IOAPIC that's 128-byte aligned.
> 

The PIIX3 IOAPIC decoder could only decode addresses on a 1K
granularity, but I don't think that was architectural.  I will try to ask.

	-hpa
-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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