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

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Date:	Fri, 26 Aug 2011 11:21:53 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.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 11:09 AM, Cyrill Gorcunov wrote:
> 
> Yes, one of the spec is Intel's MP specification (as far as I remember).
> Letme re-check...
> 
>  | 3.6.5 APIC Memory Mapping
>  |
>  | "Unlike the local APICs, the I/O APICs are mapped to give shared access from all
>  | processors, providing full symmetric I/O access. The default base address for the
>  | first I/O APIC is 0FEC0_0000h. Subsequent I/O APIC addresses are assigned in
>  | 4K increments. For example, the second I/O APIC is at 0FEC0_1000h. Non-default
>  | APIC base addresses can be used if the MP configuration table is provided.
>  | (Refer to Chapter 4.) However, the local APIC base address must be aligned
>  | on a 4K boundary, and the I/O APIC base address must be aligned on a 1K
>  | boundary."
> 
> Ie -- 4K increment with 1K base address. If I find other sources I have in mind
> I'll ping you.
> 

OK, so that explicitly specifies a 1K alignment.  The 4K bit seems to be
a default policy and not a requirement.

	-hpa

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