From 2f1675c11a0a214855ff6cba23aca239eef7a5fb Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Mon, 4 Dec 2006 20:25:47 +0100 Subject: [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 Signed-off-by: Russell King --- arch/arm/mach-sa1100/generic.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) (limited to 'arch/arm/mach-sa1100') diff --git a/arch/arm/mach-sa1100/generic.c b/arch/arm/mach-sa1100/generic.c index 4575f316e14..e510295c258 100644 --- a/arch/arm/mach-sa1100/generic.c +++ b/arch/arm/mach-sa1100/generic.c @@ -20,6 +20,7 @@ #include #include +#include #include #include #include @@ -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; } -- cgit v1.2.3