1 files changed, 74 insertions, 0 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index d58d74cf570e..587d251be454 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -32,6 +32,78 @@ static void rtc_device_release(struct device *dev)
         kfree(rtc);
 }
 
+#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;
+
+        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,
+                                xtime.tv_sec - oldtime,
+                                xtime.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
+
+
 /**
  * rtc_device_register - register w/ RTC class
  * @dev: the device to register
@@ -143,6 +215,8 @@ static int __init rtc_init(void)
                 printk(KERN_ERR "%s: couldn't create class\n", __FILE__);
                 return PTR_ERR(rtc_class);
         }
+        rtc_class->suspend = rtc_suspend;
+        rtc_class->resume = rtc_resume;
         rtc_dev_init();
         rtc_sysfs_init(rtc_class);
         return 0;