Re: [Qemu-devel] [PATCH 0/4] qdev: switch reset to post-order, clean up PCI reset

[Paolo Bonzini]

Il 06/10/2013 22:34, Paolo Bonzini ha scritto:
> Il 06/10/2013 20:28, Michael S. Tsirkin ha scritto:
>>>>> For each PCI device I tried creating a VM with an instance of it (a few
>>>>> devices at a time), and did VM resets.  Earlier versions were tested by
>>>>> the guy who reported the SCSI problems.
>>>>
>>>> x86 kvm only?
>>>
>>> Yes.
>>
>> Hmm, I'm not sure that's enough for this kind of change.
> 
> I'll do more tests though, from looking at the source code, I'm not sure
> what could happen depending on the host bridge.

Did more tests, PPC g3beige and PPC64 mac99 both work.

I also tested resetting the secondary bus of a PCI bridge (via setpci),
and it also works as expected.

Finally, I looked more at the history of the code to justify patch 2.

Initially, zeroing the irq_state was added in commit 6eaa684 (Add
pci_bus_reset() function., 2009-06-17) to deal with this issue:

>> Shouldn't each device's reset function bring its line low, thus zeroing  
>> the irq_state naturally?
>>
>> If not, we have a bug somewhere.  Note we have exactly the same issue  
>> with save/restore.
>>
> They should, but I haven't found one that does.

More registers were then cleared by pci_device_reset in your commit
c0b1905 (qemu/pci: reset device registers on bus reset, 2009-09-16).
Deasserting interrupts explicitly came in later as part of PCI bus and
FLR support in commit 4c92325 (pci: deassert intx on reset.,
2011-01-20).  That should be the point where the code starts following
the invariant of patch 2.

Paolo