1 files changed, 48 insertions, 17 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 4194e59e14cd..01a7df5317c1 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -41,20 +41,41 @@ static void rtc_device_release(struct device *dev)
  * system's wall clock; restore it on resume().
  */
 
-static time_t           oldtime;
-static struct timespec  oldts;
+static struct timespec old_rtc, old_system, old_delta;
+
 
 static int rtc_suspend(struct device *dev, pm_message_t mesg)
 {
         struct rtc_device       *rtc = to_rtc_device(dev);
         struct rtc_time         tm;
-
+        struct timespec         delta, delta_delta;
         if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
                 return 0;
 
+        /* snapshot the current RTC and system time at suspend*/
         rtc_read_time(rtc, &tm);
-        ktime_get_ts(&oldts);
-        rtc_tm_to_time(&tm, &oldtime);
+        getnstimeofday(&old_system);
+        rtc_tm_to_time(&tm, &old_rtc.tv_sec);
+
+
+        /*
+         * To avoid drift caused by repeated suspend/resumes,
+         * which each can add ~1 second drift error,
+         * try to compensate so the difference in system time
+         * and rtc time stays close to constant.
+         */
+        delta = timespec_sub(old_system, old_rtc);
+        delta_delta = timespec_sub(delta, old_delta);
+        if (abs(delta_delta.tv_sec)  >= 2) {
+                /*
+                 * if delta_delta is too large, assume time correction
+                 * has occured and set old_delta to the current delta.
+                 */
+                old_delta = delta;
+        } else {
+                /* Otherwise try to adjust old_system to compensate */
+                old_system = timespec_sub(old_system, delta_delta);
+        }
 
         return 0;
 }
@@ -63,32 +84,42 @@ static int rtc_resume(struct device *dev)
 {
         struct rtc_device       *rtc = to_rtc_device(dev);
         struct rtc_time         tm;
-        time_t                  newtime;
-        struct timespec         time;
-        struct timespec         newts;
+        struct timespec         new_system, new_rtc;
+        struct timespec         sleep_time;
 
         if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
                 return 0;
 
-        ktime_get_ts(&newts);
+        /* snapshot the current rtc and system time at resume */
+        getnstimeofday(&new_system);
         rtc_read_time(rtc, &tm);
         if (rtc_valid_tm(&tm) != 0) {
                 pr_debug("%s:  bogus resume time\n", dev_name(&rtc->dev));
                 return 0;
         }
-        rtc_tm_to_time(&tm, &newtime);
-        if (newtime <= oldtime) {
-                if (newtime < oldtime)
+        rtc_tm_to_time(&tm, &new_rtc.tv_sec);
+        new_rtc.tv_nsec = 0;
+
+        if (new_rtc.tv_sec <= old_rtc.tv_sec) {
+                if (new_rtc.tv_sec < old_rtc.tv_sec)
                         pr_debug("%s:  time travel!\n", dev_name(&rtc->dev));
                 return 0;
         }
-        /* calculate the RTC time delta */
-        set_normalized_timespec(&time, newtime - oldtime, 0);
 
-        /* subtract kernel time between rtc_suspend to rtc_resume */
-        time = timespec_sub(time, timespec_sub(newts, oldts));
+        /* calculate the RTC time delta (sleep time)*/
+        sleep_time = timespec_sub(new_rtc, old_rtc);
+
+        /*
+         * Since these RTC suspend/resume handlers are not called
+         * at the very end of suspend or the start of resume,
+         * some run-time may pass on either sides of the sleep time
+         * so subtract kernel run-time between rtc_suspend to rtc_resume
+         * to keep things accurate.
+         */
+        sleep_time = timespec_sub(sleep_time,
+                        timespec_sub(new_system, old_system));
 
-        timekeeping_inject_sleeptime(&time);
+        timekeeping_inject_sleeptime(&sleep_time);
         return 0;
 }