Re: [Xen-devel] PCI Pass-through in Xen ARM - Draft 2.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jul 31, 2015 at 11:32:19AM +0100, Ian Campbell wrote:
> On Fri, 2015-07-31 at 09:05 +0100, Ian Campbell wrote:
> > On Fri, 2015-07-31 at 13:16 +0530, Manish Jaggi wrote:
> > > > > Secondly, the vdev-X entry is created async by dom0 watching on 
> > > > > event.
> 
> Stefano points out that there are, confusingly, two nodes in xenstore
> relating to the virtual-SBDF.
> 
> vdev-X is written by pciback and is read by pcifront, it is effectively
> there to communicate the vSBDF to the guest.
> 
> vdevfn-X is written by the toolstack (libxl_create_pci_backend_device) to
> tell the backend (pciback, or qemu in x86/HVM configurations using old
> qemu) the vSBDF to be associated with the device.
> 
> It looks like vdevfn-X is not actually currently supported by pciback in
> Linux (seemingly only the x86/HVM qemu backend consumes it). I think we
> should add that support to pciback for consistency with the qemu based
> backend used by x86/HVM guests.
> 
> The names are a certainly a bit confusing. We could add a new key with a
> better name to communicate the vSBDF from toolstack->backend, but itseems
> to me to be that would just adding even more confusion, so I recommend we
> don't do that.
> 
> Once pciback supports vdevfn then libxl will be able to choose the PCI bus
> layout for ARM guests in the case where the use has not requested an
> explicit vdevfn for the device.
> 
> Does that make sense?

Yes.
> 
> Ian.
> 
> 
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