From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@citrix.com>
Subject: Re: PCI Pass-through in Xen ARM - Draft 2.
Date: Tue, 14 Jul 2015 18:58:29 +0200
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>, Manish Jaggi <mjaggi@caviumnetworks.com>, Prasun Kapoor <Prasun.kapoor@caviumnetworks.com>, "Kumar,
	Vijaya" <Vijaya.Kumar@caviumnetworks.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, Stefano Stabellini <stefano.stabellini@citrix.com>, "Kulkarni,
	Ganapatrao" <Ganapatrao.Kulkarni@caviumnetworks.com>
List-Id: xen-devel@lists.xenproject.org

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.

Although, based on the x86 code, Xen should be able to translate the BDF 
into the requester ID...

Regards,

-- 
Julien Grall