From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [v5][PATCH 0/5] xen: add Intel IGD passthrough
	support
Date: Wed, 25 Jun 2014 11:54:22 +0200
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To: "Chen, Tiejun" <tiejun.chen@intel.com>, "Michael S. Tsirkin" <mst@redhat.com>
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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