Re: [Xen-devel] [PATCH v9 15/19] xen: create a Xen nexus to use in PV/PVH

On 01/09/14 11:30, Roger Pau Monné wrote:
> On 07/01/14 15:27, Julien Grall wrote:
>> On 01/07/2014 08:29 AM, Roger Pau Monné wrote:
>>> On 06/01/14 12:33, Julien Grall wrote:
>>>>
>>>> On 01/06/2014 09:35 AM, Roger Pau Monné wrote:
>>>>> On 05/01/14 22:55, Julien Grall wrote:
>>>>>>
>>>>>> On 01/02/2014 03:43 PM, Roger Pau Monne wrote:
>>>>>>> Introduce a Xen specific nexus that is going to be in charge for
>>>>>>> attaching Xen specific devices.
>>>>>> Now that we have a xenpv bus, do we really need a specific nexus for
>>>>>> Xen?
>>>>>> We should be able to use the identify callback of xenpv to create the
>>>>>> bus.
>>>>>>
>>>>>> The other part of this patch can be merged in the patch #14 "Introduce
>>>>>> xenpv bus and a dummy pvcpu device".
>>>>> On x86 at least we need the Xen specific nexus, or we will fall back to
>>>>> use the legacy nexus which is not what we really want.
>>>>>
>>>> Oh right, in any case can we use the identify callback of xenpv to add
>>>> the bus?
>>> AFAICT this kind of bus devices don't have a identify routine, and they
>>> are usually added manually from the specific nexus, see acpi or legacy.
>>> Could you add the device on ARM when you detect that you are running as
>>> a Xen guest, or in the generic ARM nexus if Xen is detected?
>> Is there any reason to not add identify callback? If it's possible, I
>> would like to avoid as much as possible #ifdef XENHVM in ARM code.
> Maybe the x86 world is really different from the ARM world in how nexus
> works, but I rather prefer to have a #ifdef XENHVM and a BUS_ADD_CHILD
> that attaches the xenpv bus in the generic ARM nexus rather than having
> something that completely diverges from what buses usually do in
> FreeBSD. It's going to be much more difficult to track in case of bugs,
> and it's not what people expects, but that's just my opinion. I can
> certainly add the identify routine if there's an agreement that it's the
> best way to deal with it.
>
> Roger.
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Attaching sub-devices to nexus using device_identify() is the usual way
to do this kind of thing. Note that if you do this, your device_probe()
routine should return BUS_PROBE_NOWILDCARD to deal with platforms (ARM,
MIPS, PowerPC, sparc64) with real autoconfigured devices hanging
directly from nexus.
-Nathan