[PATCH] Document Linux's memory barriers [try #4]

[Paul Mackerras]

Alan Cox writes:

> On Fri, Mar 10, 2006 at 10:34:53AM +1100, Paul Mackerras wrote:
> > MMIO accesses are done under a spinlock, and that if your driver is
> > missing them then that is a bug.  I don't think it makes sense to say
> > that mmiowb is required "on some systems".
> 
> Agreed. But if it is missing it may not be a bug. It depends what the lock
> actually protects.

True.  What I want is a statement that if one of the purposes of the
spinlock is to provide ordering of the MMIO accesses, then leaving out
the mmiowb is a bug.  I want it to be like the PCI DMA API in that
drivers are required to use it even on platforms where it's a no-op.

Paul.