From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [v5][PATCH 0/5] xen: add Intel IGD passthrough
	support
Date: Wed, 25 Jun 2014 13:00:50 +0300
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: peter.maydell@linaro.org, xen-devel@lists.xensource.com, stefano.stabellini@eu.citrix.com, allen.m.kay@intel.com, Kelly.Zytaruk@amd.com, qemu-devel@nongnu.org, anthony.perard@citrix.com, anthony@codemonkey.ws, yang.z.zhang@intel.com, "Chen, Tiejun" <tiejun.chen@intel.com>
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On Wed, Jun 25, 2014 at 11:54:22AM +0200, Paolo Bonzini wrote:
> Il 25/06/2014 11:50, Chen, Tiejun ha scritto:
> >>
> >>For past devices, we know which BARs they use.  For future devices, it
> >>would be nice if the PCH/MCH backdoor was specified so that we know they
> >>will leave a free BAR for virtualization.
> >>
> >
> >Now I'm a bit confused about BAR here.
> >
> >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?
> 
> The video device.  If the host device does not have the BAR (which will be
> the common case), QEMU can emulate it like this:
> 
> - offsets 0x0000..0x0fff map to configuration space of the host MCH
> 
> - offsets 0x1000..0x1fff map to configuration space of the host PCH
> 
> Of course this is only limited to offsets that are needed by the driver.
> 
> Paolo

Ow.
If you need hacks like this, describe this in ACPI.
But I really hope not.

-- 
MST