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

[Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>]

On Tuesday 14 July 2015 11:31 PM, Stefano Stabellini wrote:
> On Tue, 14 Jul 2015, Julien Grall wrote:
> > Hi Stefano,
> >
> > On 14/07/2015 18:46, Stefano Stabellini wrote:
> > > > > Linux provides a function (pci_for_each_dma_alias) which will return a
> > > > > requester ID for a given PCI device. It appears that the BDF (the 's' of
> > > > > sBDF
> > > > > is only internal to Linux and not part of the hardware) is equal to the
> > > > > requester ID on your platform but we can't assume it for anyone else.
> > > > The PCI Express Base Specification states that the requester ID is "The
> > > > combination of a Requester's Bus Number, Device Number, and Function
> > > > Number that uniquely identifies the Requester."
> > > >
> > > > I think it is safe to assume BDF = requester ID on all platforms.
> > > With the catch that in case of ARI devices
> > > (http://pcisig.com/sites/default/files/specification_documents/ECN-alt-rid-interpretation-070604.pdf),
> > > BDF is actually BF because the device number is always 0 and the
> > > function number is 8 bits.
> > And some other problem such as broken PCI device...
> > Both Xen x86 (domain_context_mapping in drivers/passthrough/vtd/iommu.c) and
> > Linux (pci_dma_for_each_alias) use a code more complex than requesterID = BDF.
> >
> > So I don't think we can use requesterID = BDF in physdev op unless we are
> > *stricly* sure this is valid.
> The spec is quite clear about it, but I guess there might be hardware quirks.
Can we keep this open and for now till there is agreement make 
requesterid = bdf.
If you are ok, I will update and send Draft 3.
> > Although, based on the x86 code, Xen should be able to translate the BDF into
> > the requester ID...
> Yes, that is a good point.

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