From e5ad334b609eeeaa6bd823419bbd7d6d13cd0349 Mon Sep 17 00:00:00 2001
From: John Stultz <john.stultz@linaro.org>
Date: Tue, 4 Sep 2012 12:42:27 -0400
Subject: [PATCH] --- yaml --- r: 333871 b: refs/heads/master c:
 b3c869d35b9b014f63ac0beacd31c57372084d01 h: refs/heads/master i:   333869:
 294b42969013c8519c0c71f945643c903cf5f8f5   333867:
 786c8c412763f94cbb8c5cbf099bc06a1fafaed4   333863:
 dbab111b268f51e5e614f6fdec1ac8cfd5577a46   333855:
 88ced7231956a3dd7a081a33f41c2950452043af v: v3

---
 [refs]                        |  2 +-
 trunk/arch/x86/kernel/setup.c |  3 +++
 trunk/include/linux/jiffies.h | 15 ++-------------
 trunk/kernel/time/jiffies.c   | 32 +++++++++++++++++++++++++++++++-
 4 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/[refs] b/[refs]
index 52bc36aa63ff..3718649990c7 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 7916a1f14f06ac93e4cec81139fe4f7ec13b572c
+refs/heads/master: b3c869d35b9b014f63ac0beacd31c57372084d01
diff --git a/trunk/arch/x86/kernel/setup.c b/trunk/arch/x86/kernel/setup.c
index f4b9b80e1b95..4062f15bfbdd 100644
--- a/trunk/arch/x86/kernel/setup.c
+++ b/trunk/arch/x86/kernel/setup.c
@@ -68,6 +68,7 @@
 #include <linux/percpu.h>
 #include <linux/crash_dump.h>
 #include <linux/tboot.h>
+#include <linux/jiffies.h>
 
 #include <video/edid.h>
 
@@ -1034,6 +1035,8 @@ void __init setup_arch(char **cmdline_p)
 	mcheck_init();
 
 	arch_init_ideal_nops();
+
+	register_refined_jiffies(CLOCK_TICK_RATE);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/trunk/include/linux/jiffies.h b/trunk/include/linux/jiffies.h
index 4a7e3864e80d..388edb54bfb6 100644
--- a/trunk/include/linux/jiffies.h
+++ b/trunk/include/linux/jiffies.h
@@ -51,21 +51,10 @@
 #define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
                              + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
 
-#ifdef CLOCK_TICK_RATE
-/* LATCH is used in the interval timer and ftape setup. */
-# define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
-
-/*
- * HZ is the requested value. However the CLOCK_TICK_RATE may not allow
- * for exactly HZ. So SHIFTED_HZ is high res HZ ("<< 8" is for accuracy)
- */
-# define SHIFTED_HZ (SH_DIV(CLOCK_TICK_RATE, LATCH, 8))
-#else
-# define SHIFTED_HZ (HZ << 8)
-#endif
+extern int register_refined_jiffies(long clock_tick_rate);
 
 /* TICK_NSEC is the time between ticks in nsec assuming SHIFTED_HZ */
-#define TICK_NSEC (SH_DIV(1000000UL * 1000, SHIFTED_HZ, 8))
+#define TICK_NSEC ((NSEC_PER_SEC+HZ/2)/HZ)
 
 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
diff --git a/trunk/kernel/time/jiffies.c b/trunk/kernel/time/jiffies.c
index 46da0537c10b..6629bf7b5285 100644
--- a/trunk/kernel/time/jiffies.c
+++ b/trunk/kernel/time/jiffies.c
@@ -37,7 +37,7 @@
  * requested HZ value. It is also not recommended
  * for "tick-less" systems.
  */
-#define NSEC_PER_JIFFY	((u32)((((u64)NSEC_PER_SEC)<<8)/SHIFTED_HZ))
+#define NSEC_PER_JIFFY	((NSEC_PER_SEC+HZ/2)/HZ)
 
 /* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
  * conversion, the .shift value could be zero. However
@@ -95,3 +95,33 @@ struct clocksource * __init __weak clocksource_default_clock(void)
 {
 	return &clocksource_jiffies;
 }
+
+struct clocksource refined_jiffies;
+
+int register_refined_jiffies(long cycles_per_second)
+{
+	u64 nsec_per_tick, shift_hz;
+	long cycles_per_tick;
+
+
+
+	refined_jiffies = clocksource_jiffies;
+	refined_jiffies.name = "refined-jiffies";
+	refined_jiffies.rating++;
+
+	/* Calc cycles per tick */
+	cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
+	/* shift_hz stores hz<<8 for extra accuracy */
+	shift_hz = (u64)cycles_per_second << 8;
+	shift_hz += cycles_per_tick/2;
+	do_div(shift_hz, cycles_per_tick);
+	/* Calculate nsec_per_tick using shift_hz */
+	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
+	nsec_per_tick += (u32)shift_hz/2;
+	do_div(nsec_per_tick, (u32)shift_hz);
+
+	refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
+
+	clocksource_register(&refined_jiffies);
+	return 0;
+}