MMIO and gcc re-ordering issue

[Nick Piggin]

On Tuesday 03 June 2008 18:15, Jeremy Higdon wrote:
> On Tue, Jun 03, 2008 at 02:33:11PM +1000, Nick Piggin wrote:
> > On Monday 02 June 2008 19:56, Jes Sorensen wrote:

> > > Would we be able to use Ben's trick of setting a per cpu flag in
> > > writel() then and checking that in spin unlock issuing the mmiowb()
> > > there if needed?
> >
> > Yes you could, but your writels would still not be strongly ordered
> > within (or outside) spinlock regions, which is what Linus wants (and
> > I kind of agree with).
>
> Yes they would be.  Writes from the same CPU are always ordered.  Writes
> from different CPUs are not, but that's only a concern if you protect

They are not strongly ordered WRT writes to cacheable memory. If they
were, then they would not leak out of spinlocks.