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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.06.12 at 15:10, Wei Wang <wei.wang2@xxxxxxx> wrote:
> On 06/21/2012 02:45 PM, Jan Beulich wrote:
>>>>> On 21.06.12 at 14:28, Wei Wang<wei.wang2@xxxxxxx>  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).

Jan


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