1 files changed, 56 insertions, 3 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index b5e352597cbb..cd91237dbfe3 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -10,6 +10,7 @@
 
 #include <linux/mm.h>
 #include <linux/time.h>
+#include <linux/timer.h>
 #include <linux/timex.h>
 #include <linux/jiffies.h>
 #include <linux/hrtimer.h>
@@ -175,12 +176,64 @@ u64 current_tick_length(void)
         return tick_length;
 }
 
+#ifdef CONFIG_GENERIC_CMOS_UPDATE
 
-void __attribute__ ((weak)) notify_arch_cmos_timer(void)
+/* Disable the cmos update - used by virtualization and embedded */
+int no_sync_cmos_clock  __read_mostly;
+
+static void sync_cmos_clock(unsigned long dummy);
+
+static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
+
+static void sync_cmos_clock(unsigned long dummy)
+{
+        struct timespec now, next;
+        int fail = 1;
+
+        /*
+         * If we have an externally synchronized Linux clock, then update
+         * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
+         * called as close as possible to 500 ms before the new second starts.
+         * This code is run on a timer.  If the clock is set, that timer
+         * may not expire at the correct time.  Thus, we adjust...
+         */
+        if (!ntp_synced())
+                /*
+                 * Not synced, exit, do not restart a timer (if one is
+                 * running, let it run out).
+                 */
+                return;
+
+        getnstimeofday(&now);
+        if (abs(xtime.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
+                fail = update_persistent_clock(now);
+
+        next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec;
+        if (next.tv_nsec <= 0)
+                next.tv_nsec += NSEC_PER_SEC;
+
+        if (!fail)
+                next.tv_sec = 659;
+        else
+                next.tv_sec = 0;
+
+        if (next.tv_nsec >= NSEC_PER_SEC) {
+                next.tv_sec++;
+                next.tv_nsec -= NSEC_PER_SEC;
+        }
+        mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
+}
+
+static void notify_cmos_timer(void)
 {
-        return;
+        if (no_sync_cmos_clock)
+                mod_timer(&sync_cmos_timer, jiffies + 1);
 }
 
+#else
+static inline void notify_cmos_timer(void) { }
+#endif
+
 /* adjtimex mainly allows reading (and writing, if superuser) of
  * kernel time-keeping variables. used by xntpd.
  */
@@ -345,6 +398,6 @@ leave:	if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
         txc->stbcnt        = 0;
         write_sequnlock_irq(&xtime_lock);
         do_gettimeofday(&txc->time);
-        notify_arch_cmos_timer();
+        notify_cmos_timer();
         return(result);
 }