linux-kernel - Re: [PATCH] x86: Disable HPET MSI on ATI SB700/SB800

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Date:	Mon, 17 May 2010 18:56:30 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Andreas Herrmann <andreas.herrmann3@....com>
CC:	Yuhong Bao <yuhongbao_386@...mail.com>,
	venkatesh.pallipadi@...el.com, markh@...pro.net, dmarkh@....rr.com,
	andi@...stfloor.org,
	Linus Torvalds <torvalds@...ux-foundation.org>, alain@...ff.lu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Disable HPET MSI on ATI SB700/SB800

On 05/17/2010 08:59 AM, Andreas Herrmann wrote:
> On Mon, Jan 25, 2010 at 06:10:59PM +0100, Andreas Herrmann wrote:
>> On Fri, Jan 22, 2010 at 11:21:06PM -0800, Yuhong Bao wrote:
>>>
>>>> HPET MSI on platforms with ATI SB700/SB800 as they seem to have some
>>>> side-effects on floppy DMA. Do not use HPET MSI on such platforms.
>>
>> Argh, will see what information I can find about this problem ...
>
> FYI. I've tried to trigger the publication of errata information for that
> chipset. Finally this has happened.
>
> The discussed problem is indeed due to an erratum. See erratum #27 in
> http://support.amd.com/us/Embedded_TechDocs/46837.pdf
>
> The suggested workaround for this is to disable HPET MSI if LPC
> devices are used. I doubt that there is a convenient way for Linux to
> find out whether LPC devices are used. Thus I think the only solution
> to safely avoid the problem is the currently implemented quirk to
> disable HPET MSI on this chipset.

If one wanted, you could disable HPET MSI on this chipset only when a 
driver requests an ISA DMA channel. Then if there's no floppy or other 
LPC DMA device present, it can stay enabled. I don't know if it's worth 
the trouble, though.
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