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Re: [Xen-devel] [PATCH 3/3] qemu-xen-trad: IGD passthrough: Expose vendor specific pci cap on host bridge.

On Tue, Aug 6, 2013 at 12:15 AM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> On Tue, Jul 16, 2013 at 01:55:20AM +0300, Pasi Kärkkäinen wrote:
>> > >>How was that diagnosed? Perhaps that information can be part of the 
>> > >>source
>> > >>code to help in the future with diagnosiing which caps are needed and
>> > >>which ones can be blacklisted?
>> > >>
>> > >
>> > >I guess that's a question mostly for Ross/Jean as they're the original 
>> > >authors of the patch?
>> >
>> > We discovered the issue with Windows guests running the vendor
>> > drivers for the passed in IGD graphics device. Under certain
>> > circumstances (resuming from S3/S4 IIRC), the guest would BSOD. I
>> > finally tracked it down to a bad state in the resuming driver
>> > because it was not coded to handle the vendor capabilities not being
>> > present on the host bridge. BTW, those capabilities are flags
>> > indicating what features the IGD card has - their exact meaning is
>> > of course proprietary.
>> >
>> > I cannot say it was only a problem on Windows but rather that that
>> > is the only place we ever saw it.
>> >
>> > I never saw any other capabilities on the hosts bridges at that
>> > time, just vendor ones so the patch just handled that. If there were
>> > other capabilities, I would think it would have to be determined on
>> > a case by case basis whether they were included. Inclusion of each
>> > new type would have different ramifications it seems.
>> >
>> Thanks for the explanation. I guess parts of that should go to the patch 
>> description aswell..
> Now patch 2/3 has been applied to qemu-traditional, so only this patch 3/3 is 
> missing from qemu-traditional from this series.
> Any other changes outstanding? or only to add some of Ross's comments to the 
> patch description (and/or sources) ?
I'll have to rework this patch -- Jan believe the code is not very
clean with regard to offset / size handling.

I proposed an alternative to shadow the registers into the PCI config
space of the emulated host controller.
There seems no objection on this proposal. I'll do it when I got some
spare time.

> Thanks,
> -- Pasi

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