> I find this hard to believe. There's always the possibility that some
> part of the system doesn't support ACS so if the PCI bus addresses and
> IOVA overlap there's a good chance that P2P and ATS won't work at all on
> some hardware.
I tend to agree but this comes down to how IOVA addresses are generated in the
kernel. Alex (or anyone else) can you point to where IOVA addresses are
generated? As Logan stated earlier, p2pdma bypasses this and programs the PCI
bus address directly but other IO going to the same PCI EP may flow through the
IOMMU and be programmed with IOVA rather than PCI bus addresses.
> I prefer
> the option to disable the ACS bit on boot and let the existing code put
> the devices into their own IOMMU group (as it should already do to
> support hardware that doesn't have ACS support).
+1
Stephen
