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parisc: fix ldcw inline assembler

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There are two reasons to expose the memory *a in the asm:

1) To prevent the compiler from discarding a preceeding write to *a, and
2) to prevent it from caching *a in a register over the asm.

The change has had a few days testing with a SMP build of 2.6.22.19
running on a rp3440.

This patch is about the correctness of the __ldcw() macro itself.
The use of the macro should be confined to small inline functions
to try to limit the effect of clobbering memory on GCC's optimization
of loads and stores.

Signed-off-by: Dave Anglin <dave.anglin@nrc-cnrc.gc.ca>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
This commit is contained in:
Helge Deller 2009-04-30 21:39:45 +00:00 committed by Kyle McMartin
parent 4fb11781a0
commit 7d17e27631
1 changed files with 2 additions and 2 deletions
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4
arch/parisc/include/asm/system.h
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@ -168,8 +168,8 @@ static inline void set_eiem(unsigned long val)
/* LDCW, the only atomic read-write operation PA-RISC has. *sigh*. */
#define __ldcw(a) ({ \
unsigned __ret; \
__asm__ __volatile__(__LDCW " 0(%1),%0" \
: "=r" (__ret) : "r" (a)); \
__asm__ __volatile__(__LDCW " 0(%2),%0" \
: "=r" (__ret), "+m" (*(a)) : "r" (a)); \
__ret; \
})