+#if defined(CONFIG_PM) && defined(CONFIG_RTC_HCTOSYS_DEVICE)
+
+/*
+ * On suspend(), measure the delta between one RTC and the
+ * system's wall clock; restore it on resume().
+ */
+
+static struct timespec delta;
+static time_t oldtime;
+
+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 ts = current_kernel_time();
+
+ if (strncmp(rtc->dev.bus_id,
+ CONFIG_RTC_HCTOSYS_DEVICE,
+ BUS_ID_SIZE) != 0)
+ return 0;
+
+ rtc_read_time(rtc, &tm);
+ rtc_tm_to_time(&tm, &oldtime);
+
+ /* RTC precision is 1 second; adjust delta for avg 1/2 sec err */
+ set_normalized_timespec(&delta,
+ ts.tv_sec - oldtime,
+ ts.tv_nsec - (NSEC_PER_SEC >> 1));
+
+ return 0;
+}
+
+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;
+
+ if (strncmp(rtc->dev.bus_id,
+ CONFIG_RTC_HCTOSYS_DEVICE,
+ BUS_ID_SIZE) != 0)
+ return 0;
+
+ rtc_read_time(rtc, &tm);
+ if (rtc_valid_tm(&tm) != 0) {
+ pr_debug("%s: bogus resume time\n", rtc->dev.bus_id);
+ return 0;
+ }
+ rtc_tm_to_time(&tm, &newtime);
+ if (newtime <= oldtime) {
+ if (newtime < oldtime)
+ pr_debug("%s: time travel!\n", rtc->dev.bus_id);
+ return 0;
+ }
+
+ /* restore wall clock using delta against this RTC;
+ * adjust again for avg 1/2 second RTC sampling error
+ */
+ set_normalized_timespec(&time,
+ newtime + delta.tv_sec,
+ (NSEC_PER_SEC >> 1) + delta.tv_nsec);
+ do_settimeofday(&time);
+
+ return 0;
+}
+
+#else
+#define rtc_suspend NULL
+#define rtc_resume NULL
+#endif
+
+