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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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.

>> 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.

In the case of the Guest, we (Xen) controls the memory layout. Therefore
we can expose only one ITS.

>>>>
>>>> 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,

-- 
Julien Grall

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