On Wed, 20 Feb 2019, Mikulas Patocka wrote: > > Well, actually `iowriteX' is generic and for MMIO you have `writeX'. > > See lib/iomap.c, the comment at the top and e.g. `iowrite8' there for an > > actual proof. Alpha may have an oddball implementation, but there you go. > > Drivers will assume they can do `iowriteX' to any kind of I/O resource, > > and ordering must be respected as per Documentation/memory-barriers.txt. > > So, do you think that the barrier whould be added to iowriteX and slow > down every MMIO access? We need it either for `outX' and `iowriteX' calls operating on port I/O resources, or for neither of them, both at a time, to ensure the required consistency between the two interfaces. If that badly affects MMIO (and is not required there; please remind me what the exact justification to use `mb' here is, as it's not entirely clear to me from the commit message; `mb' is a barrier and not means for a delay), then we need to find a away for `iowriteX' to tell port I/O and MMIO accesses apart and only apply the barrier for the former kind. Maciej
