revert "x86: tsc prevent time going backwards"

revert:

| commit 47001d603375f857a7fab0e9c095d964a1ea0039
| Author: Thomas Gleixner <tglx@linutronix.de>
| Date:   Tue Apr 1 19:45:18 2008 +0200
|
|     x86: tsc prevent time going backwards

it has been identified to cause suspend regression - and the
commit fixes a longstanding bug that existed before 2.6.25 was
opened - so it can wait some more until the effects are better
understood.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 4 insertions, 34 deletions

diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c
index d7498b34c8e9..f14cfd9d1f94 100644
--- a/arch/x86/kernel/tsc_32.c
+++ b/arch/x86/kernel/tsc_32.c
@@ -287,27 +287,14 @@ core_initcall(cpufreq_tsc);
 /* clock source code */
 
 static unsigned long current_tsc_khz = 0;
-static struct clocksource clocksource_tsc;
 
-/*
- * We compare the TSC to the cycle_last value in the clocksource
- * structure to avoid a nasty time-warp issue. This can be observed in
- * a very small window right after one CPU updated cycle_last under
- * xtime lock and the other CPU reads a TSC value which is smaller
- * than the cycle_last reference value due to a TSC which is slighty
- * behind. This delta is nowhere else observable, but in that case it
- * results in a forward time jump in the range of hours due to the
- * unsigned delta calculation of the time keeping core code, which is
- * necessary to support wrapping clocksources like pm timer.
- */
 static cycle_t read_tsc(void)
 {
         cycle_t ret;
 
         rdtscll(ret);
 
-        return ret >= clocksource_tsc.cycle_last ?
-                ret : clocksource_tsc.cycle_last;
+        return ret;
 }
 
 static struct clocksource clocksource_tsc = {
diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c
index 01fc9f0c39e2..947554ddabb6 100644
--- a/arch/x86/kernel/tsc_64.c
+++ b/arch/x86/kernel/tsc_64.c
@@ -11,7 +11,6 @@
 #include <asm/hpet.h>
 #include <asm/timex.h>
 #include <asm/timer.h>
-#include <asm/vgtod.h>
 
 static int notsc __initdata = 0;
 
@@ -291,34 +290,18 @@ int __init notsc_setup(char *s)
 
 __setup("notsc", notsc_setup);
 
-static struct clocksource clocksource_tsc;
 
-/*
- * We compare the TSC to the cycle_last value in the clocksource
- * structure to avoid a nasty time-warp. This can be observed in a
- * very small window right after one CPU updated cycle_last under
- * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which
- * is smaller than the cycle_last reference value due to a TSC which
- * is slighty behind. This delta is nowhere else observable, but in
- * that case it results in a forward time jump in the range of hours
- * due to the unsigned delta calculation of the time keeping core
- * code, which is necessary to support wrapping clocksources like pm
- * timer.
- */
+/* clock source code: */
 static cycle_t read_tsc(void)
 {
         cycle_t ret = (cycle_t)get_cycles();
-
-        return ret >= clocksource_tsc.cycle_last ?
-                ret : clocksource_tsc.cycle_last;
+        return ret;
 }
 
 static cycle_t __vsyscall_fn vread_tsc(void)
 {
         cycle_t ret = (cycle_t)vget_cycles();
-
-        return ret >= __vsyscall_gtod_data.clock.cycle_last ?
-                ret : __vsyscall_gtod_data.clock.cycle_last;
+        return ret;
 }
 
 static struct clocksource clocksource_tsc = {