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

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-07-07 at 14:16 +0530, Manish Jaggi wrote:
> > As asked you in the previous mail, can you please prove it? The 
> > function used to get the requester ID (pci_for_each_dma_alias) is more 
> > complex than a simple return sbdf.
> I am not sure what you would like me to prove.
> As of ThunderX Xen code we have assumed sbdf == deviceID.

Please remember that you are not writing "ThunderX Xen code" here, you
are writing generic Xen code which you happen to be testing on Thunder
X. The design and implementation does need to consider the more generic
case I'm afraid.

In particular if this is going to be a PHYSDEVOP then it needs to be
designed to be future proof, since PHYSDEVOP is a stable API i.e. it is
hard to change in the future.

I think I did ask elsewhere _why_ this was a physdev op, since I can't
see why it can't be done by the toolstack, and therefore why it can't be
a domctl.

If this was a domctl there might be scope for accepting an
implementation which made assumptions such as sbdf == deviceid. However
I'd still like to see this topic given proper treatment in the design
and not just glossed over with "this is how ThunderX does things".

Or maybe the solution is simple and we should just do it now -- i.e. can
we add a new field to the PHYSDEVOP_pci_host_bridge_add argument struct
which contains the base deviceid for that bridge (since I believe both
DT and ACPI IORT assume a simple linear mapping[citation needed])?

Ian.