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

[Manish Jaggi <mjaggi@caviumnetworks.com>]

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.