MMIO and gcc re-ordering issue

[Linus Torvalds]

On Tue, 27 May 2008, Benjamin Herrenschmidt wrote:
> 
> Yes. As it is today, tg3 for example is potentially broken on all archs
> with newer gcc unless we either add "memory" clobber to readl/writel or
> stick some wmb's in there (just a random driver I picked).
> 
> So Linus, what is your take on that matter ?

Let's just serialize the damn things, and add a memory clobber to them.

Expecting people to fix up all drivers is simply not going to happen. And 
serializing things shouldn't be *that* expensive. People who cannot take 
the expense can continue to use the magic __raw_writel() etc stuff.

			Linus