Re: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Wed, Jun 25, 2014 at 06:37:31PM +0800, Chen, Tiejun wrote:
> On 2014/6/25 18:32, Michael S. Tsirkin wrote:
> >On Wed, Jun 25, 2014 at 06:28:34PM +0800, Chen, Tiejun wrote:
> >>On 2014/6/25 18:21, Michael S. Tsirkin wrote:
> >>>On Wed, Jun 25, 2014 at 06:06:50PM +0800, Chen, Tiejun wrote:
> >>>>On 2014/6/25 17:59, Paolo Bonzini wrote:
> >>>>>Il 25/06/2014 11:55, Michael S. Tsirkin ha scritto:
> >>>>>>>You're saying we will reserve a free BAR to address those
> >>>>>>information to
> >>>>>>>expose to guest, but which device does this free BAR belong to? The
> >>>>>>video
> >>>>>>>device? Or PCH/MCH?
> >>>>>>
> >>>>>>If you just want to pass a couple of IDs, then don't, it's a waste.
> >>>>>>But I still don't know what problem you are trying to solve,
> >>>>>>looking at guest driver did not help.
> >>>>>
> >>>>>It's not just a couple of IDs, it's also random fields of the MCH
> >>>>>configuration space.  Grep drivers/gpu/drm/i915 for bridge_dev.
> >>>>>
> >>>>
> >>>>Paolo,
> >>>>
> >>>>No, we're not pointing the bridge_dev here, which is a host bridge at
> >>>>00:00.0.
> >>>>
> >>>>Here it should be a ISA bridge at 00:1f.0. Please see intel_detect_pch() 
> >>>>to
> >>>>know why we need this.
> >>>>
> >>>>Thanks
> >>>>Tiejun
> >>>>
> >>>
> >>>So what if you dont?
> >>>
> >>>         if (!pch)
> >>>                 DRM_DEBUG_KMS("No PCH found.\n");
> >>>
> >>>Is that all? Seems harmless enough.
> >>>
> >>
> >>I don't read the whole driver completely so I don't know now. I guess the
> >>driver may go other live path even without this setting in a live, or this
> >>is a real bug to this driver on Intel platform.
> >>
> >>But anyway, I think we should guarantee the driver work under the same
> >>configuration as the native in the passthrough case.
> >>
> >>Thanks
> >>Tiejun
> >
> >Just get it working as a first step. Then address theoretical
> >issues in follow-up patches.
> >
> 
> I'm not sure if we can simply. So I will post this to the driver developer
> to ask more.
> 
> Thanks
> Tiejun


Please do.
The main issue in my mind is that you are implementing a non working
ISA bridge.
If guest uses it for anything - boom.


-- 
MST

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