MMIO and gcc re-ordering issue

[Linus Torvalds]

On Tue, 27 May 2008, Linus Torvalds wrote:
> 
> Here's a UNTESTED patch for x86 that may or may not compile and work, and 
> which serializes (on a compiler level) the IO accesses against regular 
> memory accesses.

Ok, so it at least boots on x86-32. Thus probably on x86-64 too (since the 
code is now shared). I didn't look at whether it generates much bigger 
code due to the potential extra serialization, but some of the code 
generation I looked at looked fine.

IOW, it doesn't at least create any _obviously_ worse code, and it should 
be arguably safer than assuming the compiler does volatile accesses the 
way we want it to.

		Linus