Re: [Qemu-devel] [PATCH 1/4] hw/pcie: fix Extended Configuration Space for devices with no Extended Capabilities

[Marcel Apfelbaum <marcel@redhat.com>]

On 01/10/2017 05:13 AM, Michael S. Tsirkin wrote:
> On Wed, Jan 04, 2017 at 09:57:15PM +0200, Marcel Apfelbaum wrote:
>> Absence of any Extended Capabilities is required to be
>> indicated by an Extended Capability header with a Capability ID of
>> 0000h, a Capability Version of 0h, and a Next Capability Offset of 000h.
>>
>> Instead of inserting a 'NULL' capability is simpler to mark the start
>> of the Extended Configuration Space as read-only to achieve the same
>> behaviour.
>>
>> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
>
> Kind of hacky and only theoretical - I don't think any guest writes
> there - but ok.

I agree is theoretical, but Windows PCI Hardware Compliance WHQL tests find it.

  However I think
> 1. we should init config to 0 too

What do you mean? Have a 'Null' capability for regular PCI capabilities list?
I'll have a look on the spec to see if is required.

> 2. this needs a compat flag

Sure, I'll add one.

Thanks,
Marcel

>
>> ---
>>  hw/pci/pcie.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
>> index 99cfb45..62c1def 100644
>> --- a/hw/pci/pcie.c
>> +++ b/hw/pci/pcie.c
>> @@ -109,6 +109,9 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
>>                   PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);
>>
>>      pci_set_word(dev->wmask + pos + PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_EETLPPB);
>> +
>> +    /* read-only to behave like a 'NULL' Extended Capability Header */
>> +    pci_set_long(dev->wmask + PCI_CONFIG_SPACE_SIZE, 0);
>>      return pos;
>>  }
>>
>> --
>> 2.5.5