Re: [Qemu-ppc] [PATCH|RFC 1/1] pci: allow 0 address for PCI IO/MEM regions

[Laurent Vivier]

On 22/07/2015 18:47, Alexander Graf wrote:
> On 07/22/15 18:17, Michael S. Tsirkin wrote:
>> On Wed, Jul 22, 2015 at 01:54:59PM +0200, Laurent Vivier wrote:
>>> From: Michael Roth <address@hidden>
>>>
>>> Some kernels program a 0 address for io regions. PCI 3.0 spec
>>> section 6.2.5.1 doesn't seem to disallow this.
>>>
>>> Signed-off-by: Michael Roth <address@hidden>
>>> [lvivier: add accept_addr_0 in PCIBus to conditionally allow addr 0,
>>>   as this can break other architectures]
>>> Signed-off-by: Laurent Vivier <address@hidden>
>> I guess it's a solution - though I'd rather fix up priorities
>> for PC and others.
> 
> Won't this break Linux? IIRC there was a check in Linux that declares
> IO==0 addresses as invalid on PCI enumeration.

Well, without this patch, it doesn't work (try 2.4.0-rcX -M pseries and
add a virtio-net-pci card).

But the address 0 appears only on PCI hotplug. The first card we add
"lively" is always inserted with address 0 for BAR0 (even if we have
already a PCI card on the bus).

If we add a second card, it works well (as it can't have the address 0
again).

If we reboot the machine, the cards are reordered and have "valid" (!=
0) addresses.

Do you suspect a bug in the kernel PCI hotplug functions ?

Laurent