[PATCH] clocksource: Add verification (watchdog) helper

The TSC needs to be verified against another clocksource.  Instead of using
hardwired assumptions of available hardware, provide a generic verification
mechanism.  The verification uses the best available clocksource and handles
the usability for high resolution timers / dynticks of the clocksource which
needs to be verified.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 23 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index 4b088fcadb3f..b68a21a82e17 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -832,30 +832,33 @@ EXPORT_SYMBOL(do_settimeofday);
  *
  * Accumulates current time interval and initializes new clocksource
  */
-static int change_clocksource(void)
+static void change_clocksource(void)
 {
         struct clocksource *new;
         cycle_t now;
         u64 nsec;
+
         new = clocksource_get_next();
-        if (clock != new) {
-                now = clocksource_read(new);
-                nsec =  __get_nsec_offset();
-                timespec_add_ns(&xtime, nsec);
-
-                clock = new;
-                clock->cycle_last = now;
-                printk(KERN_INFO "Time: %s clocksource has been installed.\n",
-                       clock->name);
-                return 1;
-        }
-        return 0;
+
+        if (clock == new)
+                return;
+
+        now = clocksource_read(new);
+        nsec =  __get_nsec_offset();
+        timespec_add_ns(&xtime, nsec);
+
+        clock = new;
+        clock->cycle_last = now;
+
+        clock->error = 0;
+        clock->xtime_nsec = 0;
+        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
+
+        printk(KERN_INFO "Time: %s clocksource has been installed.\n",
+               clock->name);
 }
 #else
-static inline int change_clocksource(void)
-{
-        return 0;
-}
+static inline void change_clocksource(void) { }
 #endif
 
 /**
@@ -869,7 +872,7 @@ int timekeeping_is_continuous(void)
         do {
                 seq = read_seqbegin(&xtime_lock);
 
-                ret = clock->flags & CLOCK_SOURCE_IS_CONTINUOUS;
+                ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
 
         } while (read_seqretry(&xtime_lock, seq));
 
@@ -1124,11 +1127,7 @@ static void update_wall_time(void)
         clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 
         /* check to see if there is a new clocksource to use */
-        if (change_clocksource()) {
-                clock->error = 0;
-                clock->xtime_nsec = 0;
-                clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
-        }
+        change_clocksource();
 }
 
 /*