[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>
diff --git a/arch/arm/mach-sa1100/generic.c b/arch/arm/mach-sa1100/generic.c
index 4575f31..e510295 100644
--- a/arch/arm/mach-sa1100/generic.c
+++ b/arch/arm/mach-sa1100/generic.c
@@ -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 @@
/*
* 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;
}