Re: [PATCH] PCI/MSI: don't disable AMD IOMMU MSI on Xen dom0

[Wei Wang <wei.wang2@amd.com>]

On 06/21/2012 03:24 PM, Jan Beulich wrote:
>>>> On 21.06.12 at 15:10, Wei Wang<wei.wang2@amd.com>  wrote:
>> On 06/21/2012 02:45 PM, Jan Beulich wrote:
>>>>>> On 21.06.12 at 14:28, Wei Wang<wei.wang2@amd.com>   wrote:
>>>> AMD IOMMU is an independent pci-e endpoint, and this function will not
>>>> be used for other purposes other than containing an iommu. So I don't
>>>> see that iommu will share bdf value with other devices.
>>>
>>> The question is not regarding bdf, but regarding whether under
>>> the same seg:bus:dev there might be multiple functions, one of
>>> which is the IOMMU, and if so, whether the IOMMU would be
>>> guaranteed to have a non-zero function number.
>>
>> In a real system (single or multiple iommu), amd iommu shares the same
>> device number with north bridge but has function number 2.. (e.g
>> bus:00.2) Howerver according to spec, it does not guaranteed to have
>> non-zero function number. So what is the problem you see if iommu uses
>> fun0 on a multi-func device?
>
> If it's on func 0 and gets hidden completely (as done by your
> partial patch), other functions won't be found when scanning
> for them (because secondary functions get looked at only
> when func 0 actually exists, as otherwise evaluating the header
> type register is invalid).

OK, understood. Then I think we do need to allow pci cfg read for iommu 
device.

Thanks
Wei

> Jan
>
>