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[ARM] 3981/1: sched_clock for PXA2xx

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Here's a 63-bit implementation of shed_clock() for PXA2xx.  The actual
period depends on the value of CLOCK_TICK_RATE and whether or not
reduced scaling factors were provided for it.

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 20:42:09 +01:00 committed by Russell King
parent 752bee178e
commit 2dc20a51dc
1 changed files with 60 additions and 0 deletions
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60
arch/arm/mach-pxa/generic.c
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@ -25,6 +25,10 @@
#include <linux/pm.h>
#include <linux/string.h>
#include <linux/sched.h>
#include <asm/cnt32_to_63.h>
#include <asm/div64.h>
#include <asm/hardware.h>
#include <asm/irq.h>
#include <asm/system.h>
@ -40,6 +44,62 @@
#include "generic.h"
/*
* This is the PXA2xx sched_clock implementation. This has a resolution
* of at least 308ns and a maximum value that depends on the value of
* CLOCK_TICK_RATE.
*
* 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.
*/
unsigned long long sched_clock(void)
{
unsigned long long v = cnt32_to_63(OSCR);
/* Note: top bit ov v needs cleared unless multiplier is even. */
#if CLOCK_TICK_RATE == 3686400
/* 1E9 / 3686400 => 78125 / 288, max value = 32025597s (370 days). */
/* The <<1 is used to get rid of tick.hi top bit */
v *= 78125<<1;
do_div(v, 288<<1);
#elif CLOCK_TICK_RATE == 3250000
/* 1E9 / 3250000 => 4000 / 13, max value = 709490156s (8211 days) */
v *= 4000;
do_div(v, 13);
#elif CLOCK_TICK_RATE == 3249600
/* 1E9 / 3249600 => 625000 / 2031, max value = 4541295s (52 days) */
v *= 625000;
do_div(v, 2031);
#else
#warning "consider fixing sched_clock for your value of CLOCK_TICK_RATE"
/*
* 96-bit math to perform tick * NSEC_PER_SEC / CLOCK_TICK_RATE for
* any value of CLOCK_TICK_RATE. Max value is in the 80 thousand
* years range which is nice, but with higher computation cost.
*/
{
union {
unsigned long long val;
struct { unsigned long lo, hi; };
} x;
unsigned long long y;
x.val = v;
x.hi &= 0x7fffffff;
y = (unsigned long long)x.lo * NSEC_PER_SEC;
x.lo = y;
y = (y >> 32) + (unsigned long long)x.hi * NSEC_PER_SEC;
x.hi = do_div(y, CLOCK_TICK_RATE);
do_div(x.val, CLOCK_TICK_RATE);
x.hi += y;
v = x.val;
}
#endif
return v;
}
/*
* Handy function to set GPIO alternate functions
*/