Re: [PATCH 02/10] arm/pci: Maintain PCI assignable list

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 11/11/20 5:25 PM, Jan Beulich wrote:
> On 11.11.2020 16:13, Oleksandr Andrushchenko wrote:
>> On 11/11/20 5:03 PM, Roger Pau Monné wrote:
>>> On Wed, Nov 11, 2020 at 02:38:47PM +0000, Oleksandr Andrushchenko wrote:
>>>> On 11/11/20 3:53 PM, Roger Pau Monné wrote:
>>>>> On Mon, Nov 09, 2020 at 02:50:23PM +0200, Oleksandr Andrushchenko wrote:
>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>>
>>>>>> The original code depends on pciback to manage assignable device list.
>>>>>> The functionality which is implemented by the pciback and the toolstack
>>>>>> and which is relevant/missing/needed for ARM:
>>>>>>
>>>>>> 1. pciback is used as a database for assignable PCI devices, e.g. xl
>>>>>>       pci-assignable-{add|remove|list} manipulates that list. So, 
>>>>>> whenever the
>>>>>>       toolstack needs to know which PCI devices can be passed through it 
>>>>>> reads
>>>>>>       that from the relevant sysfs entries of the pciback.
>>>>>>
>>>>>> 2. pciback is used to hold the unbound PCI devices, e.g. when passing 
>>>>>> through
>>>>>>       a PCI device it needs to be unbound from the relevant device 
>>>>>> driver and bound
>>>>>>       to pciback (strictly speaking it is not required that the device 
>>>>>> is bound to
>>>>>>       pciback, but pciback is again used as a database of the passed 
>>>>>> through PCI
>>>>>>       devices, so we can re-bind the devices back to their original 
>>>>>> drivers when
>>>>>>       guest domain shuts down)
>>>>>>
>>>>>> 1. As ARM doesn't use pciback implement the above with additional 
>>>>>> sysctls:
>>>>>>     - XEN_SYSCTL_pci_device_set_assigned
>>>>> I don't see the point in having this sysfs, Xen already knows when a
>>>>> device is assigned because the XEN_DOMCTL_assign_device hypercall is
>>>>> used.
>>>> But how does the toolstack know about that? When the toolstack needs to
>>>>
>>>> list/know all assigned devices it queries pciback's sysfs entries. So, with
>>>>
>>>> XEN_DOMCTL_assign_device we make that knowledge available to Xen,
>>>>
>>>> but there are no means for the toolstack to get it back.
>>> But the toolstack will figure out whether a device is assigned or
>>> not by using
>>> XEN_SYSCTL_pci_device_get_assigned/XEN_SYSCTL_pci_device_enum_assigned?
>>>
>>> AFAICT XEN_SYSCTL_pci_device_set_assigned tells Xen a device has been
>>> assigned, but Xen should already know it because
>>> XEN_DOMCTL_assign_device would have been used to assign the device?
>> Ah, I misunderstood you then. So, we only want to drop 
>> XEN_DOMCTL_assign_device
>>
>> and keep the rest.
> Was this a typo? Why would you want to drop XEN_DOMCTL_assign_device?

Indeed it was: s/XEN_DOMCTL_assign_device/XEN_SYSCTL_pci_device_set_assigned

Sorry for confusion

>
> Jan