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

[Wei Wang <wei.wang2@xxxxxxx>]

On 06/21/2012 03:24 PM, Jan Beulich wrote:
> > > > 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).
OK, understood. Then I think we do need to allow pci cfg read for iommu 
device.
Thanks
Wei

> Jan


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