On Tue, 2018-03-27 at 09:36 +1100, Benjamin Herrenschmidt wrote: > I don't kow, it used to be the case, at least that's what drove us to > define things the way we did. > > Maybe things changed, but if that's the case, nobody knows for sure, > and we probably want to get Linus POV on the matter. > > I know I still write drivers that do not add a wmb in that case because > I expect things to work without it. > > If that has changed, we probably can relax some of the barriers in our > implementations of writel on a number of architectures, but not before > auditing a bunch more drivers to make sure they have the write wmb()'s
Note also that this was the entire point behind the definition of the _relaxed() accessors, to lift that specific ordering guarantee. If you now says that memory + writel requires a wmb() in between then you made writel be identical to writel_relaxed. You might notice that Documentation/driver-api/device-io.rst makes no mention of wmb() at all. Cheers, Ben.
