MMIO and gcc re-ordering issue

[Alan Cox]

> re-ordering, even though I doubt it will be visible in practice. So if you 
> use the "__" versions, you'd better have barriers even on x86!

Are we also going to have __ioread*/__iowrite* ?

Also is the sematics of __readl/__writel defined for all architectures -
I used it ages ago in the i2o drivers for speed and it got removed
because it didn't build on some platforms.

Alan