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Commit 752bee17 authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Russell King
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[ARM] 3980/1: extend the ARM Versatile sched_clock implementation from 32 to 63 bit 


 period

This provides a 63 bit clock counter guaranteed to be monotonic over a
period of 35583 days instead of a clock wrap every 179 seconds, as long
as sched_clock() is called at least once every 89 seconds.  This should
not be a problem in practice, although a kernel timer could be scheduled
every 80 seconds for example simply to call sched_clock() making sure
top bits are always synchronized if need be.

Signed-off-by: default avatarNicolas Pitre <nico@cam.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 2f1675c1

arch/arm/mach-versatile/core.c

+10 −4
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <linux/amba/bus.h>

#include <linux/amba/clcd.h>



#include <asm/cnt32_to_63.h>

#include <asm/system.h>

#include <asm/hardware.h>

#include <asm/io.h>
@@ -228,14 +229,19 @@ void __init versatile_map_io(void) 


/*

 * This is the Versatile sched_clock implementation.  This has

 * a resolution of 41.7ns, and a maximum value of about 179s.

 * a resolution of 41.7ns, and a maximum value of about 35583 days.

 *

 * The return value is guaranteed to be monotonic in that range as

 * long as there is always less than 89 seconds between successive

 * calls to this function.

 */

unsigned long long sched_clock(void)

{

	unsigned long long v;

	unsigned long long v = cnt32_to_63(readl(VERSATILE_REFCOUNTER));



	v = (unsigned long long)readl(VERSATILE_REFCOUNTER) * 125;

	do_div(v, 3);

	/* the <<1 gets rid of the cnt_32_to_63 top bit saving on a bic insn */

	v *= 125<<1;

	do_div(v, 3<<1);



	return v;

}