[linux-fbdev] Re: Fwd: Re: still no accelerated X ($#!$*)

[Geert Uytterhoeven]

On Wed, 26 Jan 2000, James A Simmons wrote:
>   I have seen alot of talk about wmb() and eieio(). Where can I find docs
> on these functions and how to program driver correctly using them? Thank
> you.

Very simple, cfr. include/asm-ppc/system.h:

/*
 * Memory barrier.
 * The sync instruction guarantees that all memory accesses initiated
 * by this processor have been performed (with respect to all other
 * mechanisms that access memory).  The eieio instruction is a barrier
 * providing an ordering (separately) for (a) cacheable stores and (b)
 * loads and stores to non-cacheable memory (e.g. I/O devices).
 *
 * mb() prevents loads and stores being reordered across this point.
 * rmb() prevents loads being reordered across this point.
 * wmb() prevents stores being reordered across this point.
 *
 * We can use the eieio instruction for wmb, but since it doesn't
 * give any ordering guarantees about loads, we have to use the
 * stronger but slower sync instruction for mb and rmb.
 */
#define mb()  __asm__ __volatile__ ("sync" : : : "memory")
#define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
#define wmb()  __asm__ __volatile__ ("eieio" : : : "memory")

The *mb() macro's are portable across the different architectures supported by
Linux. Yes, *mb are Alpha mnemonics :-)

Gr{oetje,eeting}s,
--
Geert Uytterhoeven -- Linux/{m68k~Amiga,PPC~CHRP} -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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