MMIO and gcc re-ordering issue

[Benjamin Herrenschmidt]

On Fri, 2008-05-30 at 08:07 +0200, Haavard Skinnemoen wrote:
> On Fri, 30 May 2008 11:13:23 +1000
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> 
> > > Currently, this is the only interface I know that can do native-endian
> > > accesses, so if you take it away, I'm gonna need an alternative
> > > interface that doesn't do byteswapping.  
> > 
> > Are you aware that these also don't provide any ordering guarantee ?
> 
> Yes, but I am not aware of any alternative.
> 
> I think the drivers I've written have the necessary barriers (or dma
> ops with implicit barriers) that they don't actually depend on any
> DMA vs. MMIO ordering guarantees. I hope MMIO vs. MMIO ordering is
> guaranteed though?

Only to the same address I'd say.

Ben.