> On 17 Jul 2020, at 15:49, Julien Grall <jul...@xen.org> wrote:
>
>
>
> On 17/07/2020 14:44, Bertrand Marquis wrote:
>>> On 17 Jul 2020, at 15:29, Julien Grall <jul...@xen.org> wrote:
>>>
>>>
>>>
>>> On 17/07/2020 14:22, Bertrand Marquis wrote:
>>>>>> # Emulated PCI device tree node in libxl:
>>>>>>
>>>>>> Libxl is creating a virtual PCI device tree node in the device tree
>>>>>> to enable the guest OS to discover the virtual PCI during guest
>>>>>> boot. We introduced the new config option [vpci="pci_ecam"] for
>>>>>> guests. When this config option is enabled in a guest configuration,
>>>>>> a PCI device tree node will be created in the guest device tree.
>>>>>>
>>>>>> A new area has been reserved in the arm guest physical map at which
>>>>>> the VPCI bus is declared in the device tree (reg and ranges
>>>>>> parameters of the node). A trap handler for the PCI ECAM access from
>>>>>> guest has been registered at the defined address and redirects
>>>>>> requests to the VPCI driver in Xen.
>>>>>
>>>>> Can't you deduce the requirement of such DT node based on the presence
>>>>> of a 'pci=' option in the same config file?
>>>>>
>>>>> Also I wouldn't discard that in the future you might want to use
>>>>> different emulators for different devices, so it might be helpful to
>>>>> introduce something like:
>>>>>
>>>>> pci = [ '08:00.0,backend=vpci', '09:00.0,backend=xenpt',
>>>>> '0a:00.0,backend=qemu', ... ]
>>>
>>> I like this idea :).
>>>
>>>>>
>>>>> For the time being Arm will require backend=vpci for all the passed
>>>>> through devices, but I wouldn't rule out this changing in the future.
>>>> We need it for the case where no device is declared in the config file and
>>>> the user
>>>> wants to add devices using xl later. In this case we must have the DT node
>>>> for it
>>>> to work.
>>>
>>> Are you suggesting that you plan to implement PCI hotplug?
>> No this is not in the current plan but we should not prevent this to be
>> supported some day :-)
>
> I agree that we don't want to prevent extension. But I fail to see why this
> would be an issue if we don't introduce the option "vcpi" today.
I answered that in parallel while answering to Jan.
This is needed to have no PCI device assigned when starting the guest and
assign them later using xl pci-attach
Bertrand
>
> Cheers,
>
> --
> Julien Grall
