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

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

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

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