RFC on writel and writel_relaxed

[Jason Gunthorpe]

On Mon, Mar 26, 2018 at 11:08:45AM +0000, David Laight wrote:
> > > This is a super performance critical operation for most drivers and
> > > directly impacts network performance.
> 
> Perhaps there ought to be writel_nobarrier() (etc) that never contain
> any barriers at all.
> This might mean that they are always just the memory operation,
> but it would make it more obvious what the driver was doing.

I think that is what writel_relaxed is supposed to be.

The only restriction it has is that the writes to a single device
using UC memory must be kept in program order..

Jason