MMIO and gcc re-ordering issue

Linus Torvalds torvalds at
Wed May 28 08:02:15 EST 2008

On Tue, 27 May 2008, Matthew Wilcox wrote:

> On Tue, May 27, 2008 at 10:38:22PM +0100, 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* ?
> Didn't we already define ioread*() to have loose semantics?

They are supposed to have the same semantics as readl/writel.

And yes, it's "loose", but only when compared to inb/outb (which are 
really very strict, if you want to emulate x86 - an "outb" basically is 
not only ordered, it doesn't even post the write, and waits until it has 
hit the bus!)


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