[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

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






_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel