Re: [Qemu-devel] [PATCH] hw/pci: do not update the PCI mappings while Decode (I/O or memory) bit is not set in the Command register

[Marcel Apfelbaum <marcel@redhat.com>]

On 01/14/2016 05:37 PM, Michael S. Tsirkin wrote:
> On Thu, Jan 14, 2016 at 05:23:27PM +0200, Marcel Apfelbaum wrote:
>> On 01/14/2016 04:49 PM, Michael S. Tsirkin wrote:
>>> On Thu, Jan 14, 2016 at 03:30:41PM +0100, Laszlo Ersek wrote:
>>>>> 2. The same as with pxb, disable Integrated End points for pxb-pcie.
>>>>
>>>> My vote, without a doubt.
>>>
>>> Yea, me too.
>>>
>>>
>>> On a related note: I wonder whether enough resources will be allocated
>>> to the bridge to actually make it possible to add devices by hotplug
>>> later.
>>>
>>
>> It works the same as with PXB, but now instead of having one internal PCI-bridge,
>> we will have several switches/root ports. Each of them will get the minimum MEM required by
>> PCI bridges,
>
> what does this mean? What if you add a bunch of devices
> with large memory BARs? They won't fit will they?
>

Indeed, devices with over 1 MB (I think) BARs can't be hot-plugged.
This is a known design limitation. We can think of a way to handle this,
but the real reason we have multiple root bridges is to be able to
correlate an assigned device with a NUMA node. In this case the device
will be added more likely at boot time.


I think the first step is to have *some* hot-plug support for pxb/pxb-pcie
with the current constraints, once it works we can think
of a way to make it work for devices with large BARs.

Thanks,
Marcel

>> however the IO will be allocated only if at least one legacy device
>> will be present at boot time. (this is at least what SeaBIOS does, I am going to check OVMF actions)
>>
>> Also related, checking that PCIe native hotplug works for devices behind
>> pxb-pcie bridges is my next step after I fix the current issue.
>>
>> Thanks,
>> Marcel
>>
>>>
>>>>>
>>>>> I am going to look at 1., maybe I is doable in a clean way.
>>>>
>>>> My vote: don't. :)
>>>>
>>>> Thanks
>>>> Laszlo
>>>>
>>>>> Thanks,
>>>>> Marcel
>>>>>
>>>>>
>>>>> [...]