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

[Manish Jaggi <mjaggi@caviumnetworks.com>]

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.
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.
>
> 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.

>> We can discuss this more on #xenarm irc
> Sorry I missed your ping yesterday, I had already gone home.
>
>>>>> Or you could change things such that vdevfn is always chosen by the
>>>>> toolstack for ARM, not optionally like it is on x86.
>>> For this one, the struct libxl_device_pci has a field "vdevfn", which
>>> is
>>> supposed to allow the user to specify a specific vdevfn. I'm not sure
>>> how
>>> that happens or fits together but libxl could undertake to set that on
>>> ARM
>>> in the case where the user hasn't done so, effectively taking control
>>> of
>>> the PCI bus assignment.
>>>
>>> Ian.
>>>
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@lists.xen.org
>>> http://lists.xen.org/xen-devel
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