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[ARM] 3979/1: extend the SA11x0 sched_clock implementation from 32 to 63 bit period 

This provides a 63 bit clock counter guaranteed to be monotonic over a
period of 370 days instead of a clock wrap every 19.4 minutes, as long
as sched_clock() is called at least once every 9.7 minutes which
shouldn't be a problem in practice.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Nicolas Pitre 2006-12-04 20:25:47 +01:00 committed by Russell King
parent 838ccbc35e
commit 2f1675c11a
1 changed files with 11 additions and 4 deletions
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15
arch/arm/mach-sa1100/generic.c
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@ -20,6 +20,7 @@
#include <linux/platform_device.h>
#include <asm/div64.h>
#include <asm/cnt32_to_63.h>
#include <asm/hardware.h>
#include <asm/system.h>
#include <asm/pgtable.h>
@ -118,15 +119,21 @@ EXPORT_SYMBOL(cpufreq_get);
/*
* This is the SA11x0 sched_clock implementation. This has
* a resolution of 271ns, and a maximum value of 1165s.
* a resolution of 271ns, and a maximum value of 32025597s (370 days).
*
* The return value is guaranteed to be monotonic in that range as
* long as there is always less than 582 seconds between successive
* calls to this function.
*
* ( * 1E9 / 3686400 => * 78125 / 288)
*/
unsigned long long sched_clock(void)
{
unsigned long long v;
unsigned long long v = cnt32_to_63(OSCR);
v = (unsigned long long)OSCR * 78125;
do_div(v, 288);
/* the <<1 gets rid of the cnt_32_to_63 top bit saving on a bic insn */
v *= 78125<<1;
do_div(v, 288<<1);
return v;
}