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

From: Robert Hancock
Date: Mon May 17 2010 - 20:56:39 EST

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

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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