MMIO and gcc re-ordering issue

Linus Torvalds torvalds at
Wed May 28 07:59:28 EST 2008

On Tue, 27 May 2008, Alan Cox wrote:
> > 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* ?

I doubt there is any reason to. Let's just keep them very strictly 

> 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.

Agreed - I'm not sure the __ versions are really worth it. We have them, 
but the semantics are subtle enough that most drivers will never care 
enough to really use them.

I would suggest using them mainly for architecture-specific drivers, on 
architectures where it actually matters (which is not the case on x86).


More information about the Linuxppc-dev mailing list