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

[Manish Jaggi <mjaggi@caviumnetworks.com>]

On 24/02/15 7:13 pm, Julien Grall wrote:
> On 24/02/15 00:23, Manish Jaggi wrote:
>>> 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
> You have to parse every node in the device tree and replace the
> msi-parent properties with only one ITS.
Thats the idea.
>
>>> 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).
> The DOM0 view and guest view of the hardware are different.
>
> In the case of DOM0, we want to expose the same hardware layout as the
> host. So if there is 2 ITS then we should expose the 2 ITS.
AFAIK Xen has a microkernel design and timer/mmu/smmu/gic/its are 
handled by xen and a virtualized interface is provided to the guest. So 
if none of SMMU in the layout of host is presented to dom0 the same can 
be valid for multiple ITS.
>
> In the case of the Guest, we (Xen) controls the memory layout.
For Dom0 as well.
> Therefore
> we can expose only one ITS.
If we follow 2 ITS in dom0 and 1 ITS in domU, how do u expect the Xen 
GIC ITS emulation driver to work.
It should check that request came from a dom0 handle it differently. I 
think this would be *difficult*.
>
>>>>> 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.
> So I still don't understand why you need to parse the device tree node
> for PCI device at boot time...
>
> If it doesn't trap before, you should not need to know the PCI.
>
> Regards,
>