2 files changed, 39 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index dda9be685ab6..4bb05a829be9 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -116,6 +116,8 @@ extern int do_setitimer(int which, struct itimerval *value,
 extern unsigned int alarm_setitimer(unsigned int seconds);
 extern int do_getitimer(int which, struct itimerval *value);
 extern void getnstimeofday(struct timespec *tv);
+extern void getboottime(struct timespec *ts);
+extern void monotonic_to_bootbased(struct timespec *ts);
 
 extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
 extern int timekeeping_is_continuous(void);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3d1042f82a68..728cedfd3cbd 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -36,9 +36,17 @@ EXPORT_SYMBOL(xtime_lock);
  * at zero at system boot time, so wall_to_monotonic will be negative,
  * however, we will ALWAYS keep the tv_nsec part positive so we can use
  * the usual normalization.
+ *
+ * wall_to_monotonic is moved after resume from suspend for the monotonic
+ * time not to jump. We need to add total_sleep_time to wall_to_monotonic
+ * to get the real boot based time offset.
+ *
+ * - wall_to_monotonic is no longer the boot time, getboottime must be
+ * used instead.
  */
 struct timespec xtime __attribute__ ((aligned (16)));
 struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
+static unsigned long total_sleep_time;          /* seconds */
 
 EXPORT_SYMBOL(xtime);
 
@@ -251,6 +259,7 @@ void __init timekeeping_init(void)
         xtime.tv_nsec = 0;
         set_normalized_timespec(&wall_to_monotonic,
                 -xtime.tv_sec, -xtime.tv_nsec);
+        total_sleep_time = 0;
 
         write_sequnlock_irqrestore(&xtime_lock, flags);
 }
@@ -282,6 +291,7 @@ static int timekeeping_resume(struct sys_device *dev)
 
                 xtime.tv_sec += sleep_length;
                 wall_to_monotonic.tv_sec -= sleep_length;
+                total_sleep_time += sleep_length;
         }
         /* re-base the last cycle value */
         clock->cycle_last = clocksource_read(clock);
@@ -476,3 +486,30 @@ void update_wall_time(void)
         change_clocksource();
         update_vsyscall(&xtime, clock);
 }
+
+/**
+ * getboottime - Return the real time of system boot.
+ * @ts:         pointer to the timespec to be set
+ *
+ * Returns the time of day in a timespec.
+ *
+ * This is based on the wall_to_monotonic offset and the total suspend
+ * time. Calls to settimeofday will affect the value returned (which
+ * basically means that however wrong your real time clock is at boot time,
+ * you get the right time here).
+ */
+void getboottime(struct timespec *ts)
+{
+        set_normalized_timespec(ts,
+                - (wall_to_monotonic.tv_sec + total_sleep_time),
+                - wall_to_monotonic.tv_nsec);
+}
+
+/**
+ * monotonic_to_bootbased - Convert the monotonic time to boot based.
+ * @ts:         pointer to the timespec to be converted
+ */
+void monotonic_to_bootbased(struct timespec *ts)
+{
+        ts->tv_sec += total_sleep_time;
+}