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

[Manish Jaggi <mjaggi@caviumnetworks.com>]

On 31/07/15 4:49 pm, Ian Campbell wrote:
> On Fri, 2015-07-31 at 16:37 +0530, Manish Jaggi wrote:
>> On Friday 31 July 2015 01:35 PM, Ian Campbell wrote:
>>> On Fri, 2015-07-31 at 13:16 +0530, Manish Jaggi wrote:
>>>>>> Secondly, the vdev-X entry is created async by dom0 watching on
>>>>>> event.
>>>>>> So how the tools could read back and call assign device again.
>>>>> Perhaps by using a xenstore watch on that node to wait for the
>>>>> assignment
>>>>> from pciback to occur.
>>>> As per the flow in the do_pci_add function, assign_device is called
>>>> first and based on the success xenstore entry is created.
>>>> Are you suggesting to change the sequence.
>>> Perhaps that is what it would take, yes, or maybe some other
>>> refactoring
>>> (e.g. splitting assign_device into two stages) might be the answer.
>> The hypercall from xenpciback (what I implemented) is actually making
>> the assign device in 2 stages.
>> I think the point of contention is the second stage should be from
>> toolstack.
>>
>> I think calling xc_assign_device after xenstore from the watch callback
>> is the only option.
> Only if you ignore the other option I proposed.
>
>> One question is how to split the code for ARM and x86 as this is the
>> common code.
>> Would #ifdef CONFIG_ARM64 ok with maintainers.
> No. arch hooks in libxl_$ARCH.c (with nop implementations where necessary)
> would be the way to approach this. However I still am not convinced this is
> the approach we should be taking.
>
>>> My current preference is for the suggestion below which is to let the
>>> toolstack pick the vdevfn and have pciback honour it.
>> That would duplicate code for dev-fn generation into toolstack from
>> __xen_pcibk_add_pci_dev.
> IMHO the toolstack is the correct place for this code, at least for ARM
> guests. The toolstack is, in general, responsible for all aspects of the
> guest layout. I don't think delegating the PCI bus parts of that to the
> dom0 kernel makes sense.
Ok, i will implement the same from pciback to toolstack. I am not sure 
about the complexity but will give it a try.
With this xen-pciback will not create the vdev-X entry at all.
>
> I'd not be surprised if the same turns out to be true for x86/PVH guests
> too.
> Ian.
>
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