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Blackfin arch: Fix udelay implementation

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Avoid possible overflow during 32*32->32 multiplies.

Reported-by: Marco Reppenhagen <marco.reppenhagen@auerswald.de>
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
This commit is contained in:
Michael Hennerich 2009-02-04 16:49:45 +08:00 committed by Bryan Wu
parent 972de7d929
commit 4e653e04cc
1 changed files with 5 additions and 6 deletions
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11
arch/blackfin/include/asm/delay.h
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@ -47,16 +47,15 @@ static inline void __delay(unsigned long loops)
#include <linux/param.h> /* needed for HZ */
/*
* Use only for very small delays ( < 1 msec). Should probably use a
* lookup table, really, as the multiplications take much too long with
* short delays. This is a "reasonable" implementation, though (and the
* first constant multiplications gets optimized away if the delay is
* a constant)
* close approximation borrowed from m68knommu to avoid 64-bit math
*/
#define HZSCALE (268435456 / (1000000/HZ))
static inline void udelay(unsigned long usecs)
{
extern unsigned long loops_per_jiffy;
__delay(usecs * loops_per_jiffy / (1000000 / HZ));
__delay((((usecs * HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6);
}
#endif