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m68k: Implement ndelay() based on the existing udelay() logic

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Add a ndelay macro modeled after the Coldfire udelay(). The ISP1160
driver needs a 150ns delay, so we need to have ndelay().

Signed-off-by: Michael Schmitz <schmitz@debian.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
This commit is contained in:
Michael Schmitz 2013-04-06 13:26:44 +13:00 committed by Geert Uytterhoeven
parent e6f80e87e0
commit c8ee038bd1
1 changed files with 23 additions and 0 deletions
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23
arch/m68k/include/asm/delay.h
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@ -92,5 +92,28 @@ static inline void __udelay(unsigned long usecs)
#define udelay(n) (__builtin_constant_p(n) ? \
((n) > 20000 ? __bad_udelay() : __const_udelay(n)) : __udelay(n))
/*
* nanosecond delay:
*
* ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of loops
* per microsecond
*
* 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of
* nanoseconds per loop
*
* So n / ( 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) ) would
* be the number of loops for n nanoseconds
*/
/*
* The simpler m68k and ColdFire processors do not have a 32*32->64
* multiply instruction. So we need to handle them a little differently.
* We use a bit of shifting and a single 32*32->32 multiply to get close.
* This is a macro so that the const version can factor out the first
* multiply and shift.
*/
#define HZSCALE (268435456 / (1000000 / HZ))
#define ndelay(n) __delay(DIV_ROUND_UP((n) * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6), 1000));
#endif /* defined(_M68K_DELAY_H) */