I believe that the patch itself if fine.
To test, ask Peter Holm to do a run with DMAR turned on.
I was tripped over the earlier build errors from rdtsc_ordered while looking for kmods that need unused devclass arguments to DRIVER_MODULE removed. Even with the DRIVER_MODULE issue patched, the driver still failed to build due to the rdtsc_ordered.c errors so I figured this was the better fix anyway. Users on 14 and later should be using the in-tree driver instead of this port.
Address @kib's comments. Looks nicer now.
Yep, thank you
Made the changes suggested inline.