Messages in this thread | | | Subject | Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code | From | Benjamin Herrenschmidt <> | Date | Fri, 23 May 2008 00:24:43 -0400 |
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On Tue, 2008-05-20 at 15:53 -0700, David Miller wrote: > From: Scott Wood <scottwood@freescale.com> > Date: Tue, 20 May 2008 17:43:58 -0500 > > > David Miller wrote: > > > The __volatile__ in the asm construct disallows movement of the > > > inline asm relative to statements surrounding it. > > > > > > The only reason barrier() in kernel.h needs a memory clobber is > > > because of a bug in ancient versions of gcc. In fact, I think > > > that memory clobber might even be removable. > > > > Current versions of GCC seem quite happy to move non-asm memory accesses > > around a volatile asm without a memory clobber; see the test Trent posted. > > Indeed, and even the GCC manual is clear about this.
So what is the scope of that problem ?
IE. Take an x86 version of that test, writing to memory, doing a writel to some MMIO, then another memory write, can those be re-ordered with the current x86 version of writel ?
static inline void writel(unsigned int b, volatile void __iomem *addr) { *(volatile unsigned int __force *)addr = b; }
This is becoming a serious issue...
Ben.
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