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

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Message-ID: <4E573AC2.2070908@kernel.org>
Date:	Thu, 25 Aug 2011 23:18:42 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.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>,
	Cyrill Gorcunov <gorcunov@...nvz.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 08/25/2011 06:41 PM, H. Peter Anvin wrote:
> On 08/25/2011 05:17 PM, Bjorn Helgaas wrote:
>>
>> If the OS allocated the next 128 bytes to another device, it sounds
>> like it would cause a conflict on Intel boxes.  This must be an area
>> that differs between vendors.  I haven't seen a spec that mentions 256
>> bytes as the required minimum MMIO size for IOAPICs, and apparently
>> the AMD IOAPIC decodes 240 bytes or fewer.
>>
> 
> For what it's worth, it's probably a bad idea on x86 for the OS to
> allocate addresses in the 0xFExxxxxx range...
> 
for system with more than one ioapic controllers, could have ioapic address rather low.
and those address are allocated to some pci devices BAR by BIOS.

Yinghai
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