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

[Robert Hancock]

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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