linux-kernel - Re: [PATCH 45/79] [PATCH] fix apic acking of irqs

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Date:	Thu, 20 Mar 2008 12:04:40 -0300
From:	Glauber Costa <gcosta@...hat.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	tglx@...utronix.de, mingo@...e.hu, ak@...e.de
Subject: Re: [PATCH 45/79] [PATCH] fix apic acking of irqs

Maciej W. Rozycki wrote:
> On Wed, 19 Mar 2008, Glauber de Oliveira Costa wrote:
> 
>> EOI is a write-only register. Using write around will have the effect
>> of reading it, which will make all subsequent reads of the ESR register
>> to return an error code. It was unnotices for quite a while because main sources
>> of reading the ESR register where done prior to apic interrupt enabling.
> 
>  Are you sure this actually triggers for APIC chips affected by the 
> erratum in question?  And please note that for them the effect of two 
> consecutive writes will be much more disastrous than setting a bit in the 
> ESR register.
> 
>   Maciej

I'm not _sure_, but I can't find anything in the errata list that states 
otherwise. It would be great that anyone has such a system to test it. 
But with the current conditions, it will break bootup code. In case it 
is really a problem, we'd need to make a special case for that.
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