rtc: suspend()/resume() restores system clock

RTC class suspend/resume support, re-initializing the system clock on resume
from the clock used to initialize it at boot time.

 - The reinit-on-resume is hooked to the existing RTC_HCTOSYS config
   option, on the grounds that a clock good enough for init must also
   be good enough for re-init.

 - Inlining a version of the code used by ARM, to save and restore the
   delta between a selected RTC and the current system wall-clock time.

 - Removes calls to that ARM code from AT91, OMAP1, and S3C RTCs.  This
   means that systems using those RTCs across suspend/resume will likely
   want to change their kernel configs to enable RTC_HCTOSYS.

   If HCTOSYS isn't using a second RTC (with battery?), this changes the
   system's initial date from Jan 1970 to the epoch this hardware uses:
   1998 for AT91, 2000 for OMAP1 (assuming no split power mode), etc.

This goes on top of the patch series removing "struct class_device" usage
from the RTC framework.  That's all needed for class suspend()/resume().

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-By: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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;