Re: [PATCH] Define wc_wmb, a write barrier for PCI write combining

[Jes Sorensen <jes@sgi.com>]

Bryan O'Sullivan wrote:
> On Tue, 2006-02-28 at 05:01 -0500, Jes Sorensen wrote:
> 
> 
>>Could you explain why the current mmiowb() API won't suffice for this?
>>It seems that this is basically trying to achieve the same thing.
> 
> 
> It's a no-op on every arch I care about:
> 
> #define mmiowb()
> 
> Which makes it useless.  Also, based on the comments in the qla driver,
> mmiowb() seems to have inter-CPU ordering semantics that I don't want.
> I'm thus hesitant to appropriate it for my needs.

The fact that it's a no-op may simply be because nobody on a specific
arch got to the point where it made sense to define it yet.

Anyway, based on Jesse and Jeremy's comments, then maybe the semantics
here are different. However I do think the name wc_wmb() isn't quite
defining it. If it's only to be used on mmio space, something like
mmio_wc_wmb() would probably be more descriptive.

Cheers,
Jes