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

[Michael S. Tsirkin]

On Wed, Jun 25, 2014 at 11:59:21AM +0200, 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

I did, it seems to look for device at 0,0:

        static int i915_get_bridge_dev(struct drm_device *dev)
        {
                struct drm_i915_private *dev_priv = dev->dev_private;

                dev_priv->bridge_dev = pci_get_bus_and_slot(0, PCI_DEVFN(0, 0));
                if (!dev_priv->bridge_dev) {
                        DRM_ERROR("bridge device not found\n");
                        return -1;
                }
                return 0;
        }

are you sure this is the ISA bridge device? these patches put it at 1f.