Re: [Xen-devel] RFC: [PATCH 1/3] Enhance platform support for PCI

[Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>]

On 24/02/15 3:09 am, Julien Grall wrote:
> On 23/02/2015 17:12, Manish Jaggi wrote:
> > On 23/02/15 8:45 pm, Julien Grall wrote:
> > > On 23/02/15 11:50, Manish Jaggi wrote:
> > > > On 23/02/15 4:44 pm, Julien Grall wrote:
> > > > > On 23/02/2015 10:59, Manish Jaggi wrote:
> > > > > > On 20/02/15 8:09 pm, Ian Campbell wrote:
> > > > > > > On Fri, 2015-02-20 at 19:44 +0530, Manish Jaggi wrote:
> > > > > > > > > Another option might be a new hypercall (assuming one doesn't
> > > > > > > > > already
> > > > > > > > > exist) to register a PCI bus which would take e.g. the PCI CFG 
> > > > > > > > > base
> > > > > > > > > address and return a new u16 segment id to be used for all
> > > > > > > > > subsequent
> > > > > > > > > PCI related calls. This would require the dom0 OS to hook its
> > > > > > > > > pci_bus_add function, which might be doable (more doable than
> > > > > > > > > handling
> > > > > > > > > xen_segment_id DT properties I think).
> > > > > > > > This seems ok, i will try it out.
> > > > > > > I recommend you let this subthread (e.g. the conversation with Jan)
> > > > > > > settle upon a preferred course of action before implementing any 
> > > > > > > one
> > > > > > > suggestion.
> > > > > > Ian we have also to consider for NUMA / multi node where there 
> > > > > > are two
> > > > > > or more its nodes.
> > > > > > pci0{
> > > > > >
> > > > > > msi-parent = <&its0>;
> > > > > > }
> > > > > >
> > > > > > pci1{
> > > > > >
> > > > > > msi-parent = <&its1>;
> > > > > > }
> > > > > >
> > > > > > This requires parsing pci nodes in xen and create a mapping between
> > > > > > pci
> > > > > > nodes and its. Xe would need to be aware of PCI nodes in device tree
> > > > > > prior to dom0 sending a hypercall. Adding a property to pci node in
> > > > > > device tree should be a good approach.
> > > > > Why do you need it early? Wouldn't be sufficient to retrieve those
> > > > > information when the hypercall pci_device_add is called?
> > > > The dom0/U device tree should have one 1 its node, xen should map to
> > > > specific its when trapped.
> > > The DOM0 device tree should expose the same layout as the hardware. By
> > > exposing only one ITS you make your life more complicate.
> > in what way?
> Because you have to parse all the device tree to remove the reference 
> to the second ITS. It's pointless and can be difficult to do it.
Could you please describe the case where it is difficult
> If you are able to emulate on ITS, you can do it for multiple one.
keeping it simple and similar across dom0/domUs

Consider a case where a domU is assigned two PCI devices which are 
attached to different nodes. (Node is an entity having its own cores are 
host controllers).
Currently for PCI pass-through xen has a virtual PCI bus in domU. In our 
implementation we attach a msi controller which is gic-v3-its to this 
bus in pci-front. Since there is a single bus you cannot attach 2 msi 
controllers. So xen would have to map the commands from virtual ITS to 
different physical ITS based on the deviceID / collection ID.
> > > PHYSDEVOP_pci_device_add should be called before any initialization is
> > > done. Therefore ITS should be configured for this PCI after Xen is 
> > > aware
> > > of the PCI.
> > That is for a device, I believe all devices on a host bridge are
> > serviced by a single ITS
> Why do you speak about host bridge? Do you need to configure the ITS 
> at boot time for the host bridge?
> Do you have any spec stating there is one ITS per host bridge?
I was referring to the mapping between ITS and PCI host bridge and not 
between a PCI end point / device which is added by the said hypercall. 
ITS is per node.It is always after but ITS for the PCI node is known to 
Xen before dom0 is started.
> > > IHMO, any ITS trap before this is wrong.
> > AFAIK guest always sees a virtual ITS, could you please explain what is
> > wrong in trapping.
> I never say the trapping is wrong in all case.... The "before" was 
> here for any trap before the PCI has been added to Xen is, IHMO, wrong.
There is no trap before.
> Regards,

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