[PATCH] Document Linux's memory barriers

[David Howells]

Andi Kleen <ak at suse.de> wrote:

> > > You're not supposed to do it this way anyways. The official way to access
> > > MMIO space is using read/write[bwlq]
> > 
> > True, I suppose. I should make it clear that these accessor functions imply
> > memory barriers, if indeed they do, 
> 
> I don't think they do.

Hmmm.. Seems Stephen Hemminger disagrees:

| > > 1) Access to i/o mapped memory does not need memory barriers.
| > 
| > There's no guarantee of that. On FRV you have to insert barriers as
| > appropriate when you're accessing I/O mapped memory if ordering is required
| > (accessing an ethernet card vs accessing a frame buffer), but support for
| > inserting the appropriate barriers is built into gcc - which knows the rules
| > for when to insert them.
| > 
| > Or are you referring to the fact that this should be implicit in inX(),
| > outX(), readX(), writeX() and similar?
| 
| yes

David