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 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

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
>