Re: [Qemu-devel] [PATCH V7 23/24] apci: fix PXB behaviour if used with unsupported BIOS

[Marcel Apfelbaum <marcel@redhat.com>]

On 06/01/2015 06:37 PM, Laszlo Ersek wrote:
> On 06/01/15 15:48, Marcel Apfelbaum wrote:
>> On 06/01/2015 04:28 PM, Laszlo Ersek wrote:
>>> On 06/01/15 15:05, Marcel Apfelbaum wrote:
>>>> On 06/01/2015 03:27 PM, Michael S. Tsirkin wrote:
>>>>> On Mon, Jun 01, 2015 at 03:21:19PM +0300, Marcel Apfelbaum wrote:
>>>>>> On 06/01/2015 03:17 PM, Michael S. Tsirkin wrote:
>>>>>>> On Mon, Jun 01, 2015 at 01:40:19PM +0200, Gerd Hoffmann wrote:
>>>>>>>> On Mo, 2015-06-01 at 12:44 +0300, Marcel Apfelbaum wrote:
>>>>>>>>> On 05/31/2015 09:12 PM, Michael S. Tsirkin wrote:
>>>>>>>>>> On Mon, May 25, 2015 at 06:34:01PM +0300, Marcel Apfelbaum wrote:
>>>>>>>>>>> PXB does not work with unsupported bioses, but should
>>>>>>>>>>> not interfere with normal OS operation.
>>>>>>>>>>> We don't ship them anymore, but it's reasonable
>>>>>>>>>>> to keep the work-around until we update the bios in qemu.
>>>>>>>>>>
>>>>>>>>>> We already did, did we not?
>>>>>>>>> Yes, we did, but Gerd preferred to keep this patch around.
>>>>>>>>> Adding him to thread.
>>>>>>>>
>>>>>>>> seabios bundled with qemu isn't the only possible firmware.
>>>>>>>>
>>>>>>>> We have ovmf, coreboot, qboot.
>>>>>>>
>>>>>>> ovmf is especially interesting. Marcel, did you look at what
>>>>>>> happens with pxb and ovmf?
>>>>>> No, I talked to Laszlo about it, he said ovmf is not there yet.
>>>>>> OVMF will not query the extra buses, so the devices on the extra bus
>>>>>> will not be visible.
>>>>>> Adding him to the thread.
>>>>>>
>>>>>> Thanks,
>>>>>> Marcel
>>>>>
>>>>> But does OVMF need this specific patch?
>>>> I don't think so because more than likely it doesn't scan for the extra
>>>> buses,
>>>> so it will not try to configure these devices.
>>>> Laszlo, am I right?
>>>
>>> Well, I don't know. :)
>>>
>>> First, I'm not seeing the specific patch in question (can you pls send
>>> me a URL into the web archive, or a Message-Id?)
>> Well, there are a few patches, all this series,
>> You can look for patches:
>> 13/24 hw/acpi: add support for i440fx 'snooping' root busses -> acpi
>> declarations
>> 18/24 hw/pci: introduce PCI Expander Bridge (PXB)
>> 19/24 hw/pci: inform bios if the system has extra pci root buses
>>
>> Basically we add the pxb resources to ACPI tables and then inform BIOS
>> using
>> etc/extra-pci-roots fw_config file that he has extra roots to scan.
>>
>> If the OVMF only looks for bus 0 and does not scan all possible buses
>> it will not see PXB's root bus
>
> I don't know enough about PCI to reply sensibly.
>
> I can tell you that the bus range in OVMF, from "mResAperture" in
> "PcAtChipsetPkg/PciHostBridgeDxe/PciHostBridge.c", is [0..0xff], inclusive.
>
> This bus range is then exposed in the function StartBusEnumeration() to
> the caller (which is the PCI bus driver), as an output parameter. The
> StartBusEnumeration() function has the following leading comment:
>
>> Sets up the specified PCI root bridge for the bus enumeration process.
>>
>> This member function sets up the root bridge for bus enumeration and
>> returns the PCI bus range over which the search should be performed
>> in ACPI 2.0 resource descriptor format.
>
> So, there's a chance that if those busses actually exist on the virtual
> hardware, the drivers included by OVMF from the generic edk2 source
> "will just work". It is also possible that OVMF will notice no change at
> all.
>
> Do you have a public branch, and a matching command line? The PCI
> enumeration / resource allocation spews a bunch of messages in OVMF, so
> if you placed (on the QEMU command line) some devices on one of these
> nonzero buses, then their enumeration / resource allocation, determined
> from the log, could serve as evidence. (I think this should be testable
> on a non-NUMA host, and without passthrough devices as well.)
>
> Also, I checked the actual code hunks & message body for this patch (ie.
> 23/24) on the web. Looks like I should be able to dump the ACPI tables
> in the guest, and get those dumps to you for verification. OVMF does
> delay the ACPI download until after PCI enumeration, so the state of the
> guest _CRS would be (negative or positive) proof, not lack of proof.

Hi Laszlo,
I am sorry for the late reply.
Can you please check using mst branch?
     git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git pxb
Just add to the regular command line:
     -device pxb,id=bridge1,bus_nr=4 -netdev user,id=u -device e1000,id=net2,bus=bridge1,netdev=u,addr=1

Thanks a lot for the help, we mainly want to know if there is
an architecture issue that will prevent the PXB to work with OVMF.
Marcel

>
> Thanks
> Laszlo
>
>> Thanks,
>> Marcel
>>
>>
>>> Second, recently I tested OVMF on Q35, but not just with a simple /
>>> usual command line invocation -- I tested it on a Q35 machine configured
>>> by libvirt. That's a very different animal.
>>>
>>> While it exposed a problem in OVMF's own boot order processing:
>>>
>>> https://github.com/tianocore/edk2/commit/feca17fa4b
>>>
>>> I was surprised to see that the PCI bus driver enumerated devices behind
>>> two bridges no less without any problems. So, bridges off the one root
>>> bridge should work, but several root bridges probably won't. (Exposing
>>> root bridges is the responsibility of another driver, and they are not
>>> enumerable in the usual way.)
>>>
>>> Thanks
>>> Laszlo
>>>
>>
>