diff options
| author | Nicolas Pitre <nico@cam.org> | 2006-12-04 20:29:21 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2006-12-07 16:06:53 +0000 |
| commit | 752bee178ee107aa3dd87a9aeba970444034c6fb (patch) | |
| tree | 7bc5f554781182c88602c2dd43ddd664a32aac24 /arch | |
| parent | 2f1675c11a0a214855ff6cba23aca239eef7a5fb (diff) | |
[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: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm/mach-versatile/core.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/arch/arm/mach-versatile/core.c b/arch/arm/mach-versatile/core.c index 3b8576111c1..998b398df30 100644 --- a/arch/arm/mach-versatile/core.c +++ b/arch/arm/mach-versatile/core.c @@ -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; } |