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 d58d74cf570..587d251be45 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;