PCI rework

[Benjamin Herrenschmidt]

> Oh, I see you must be talking about the xf86(Read|Write)Mmio* 
> routines... do we really need those anymore?  Looks like BSD on Alpha 
> might use them, but are there any platforms that we care about that 
> need them?  If they're really necessary they could be added to 
> libpciaccess (though preferably w/o the silly extra layer of 
> indirection that MMIO_IN* -> xf86ReadMmio* have).

We certainly need to provide access routines for MMIO & PIO instead of
having every driver having it's own brokem crap... 

It's been an historical pain that X didn't handle proper memory barriers
for IOs for example...

It needs IO & MMIO accessors for non write combined (call them
barrierified) register accesses, it needs the ability to do "raw" access
for non-side-effect memory like the framebuffer and it needs an explicit
barrier to put in between those 2.

Ben.