rtc: restore alarm after resume

Some platform firmware may interfere with the RTC alarm over suspend,
resulting in the kernel and hardware having different ideas about system
state but also potentially causing problems with firmware that assumes the
OS will clean this case up.  This patch saves the RTC alarm state on
suspend and will restore it on resume if the alarm has not yet fired - if
it has, it will clear the RTC alarm.



The case we've seen is Intel Rapid Start, which is a firmware-mediated
feature that automatically transitions systems from suspend-to-RAM to
suspend-to-disk without OS involvement.  It does this by setting the RTC
alarm and a flag that indicates that on wake it should perform the
transition rather than re-starting the OS.  However, if the OS has set a
wakeup alarm that would wake the machine earlier, it refuses to overwrite
it and allows the system to wake instead.

This fails in the following situation:

1) User configures Intel Rapid Start to transition after (say) 15
minutes
2) User suspends to RAM. Firmware sets the wakeup alarm for 15 minutes
in the future
3) User resumes after 5 minutes. Firmware does not reset the alarm, and
as such it is still set for 10 minutes in the future
4) User suspends after 5 minutes. Firmware notices that the alarm is set
for 5 minutes in the future, which is less than the 15 minute transition
threshold. It therefore assumes that the user wants the machine to wake
in 5 minutes
5) System resumes after 5 minutes

The worst case scenario here is that the user may have put the system in a
bag between (4) and (5), resulting in it running in a confined space and
potentially overheating.  This seems reasonably important.  The Rapid
Start support code got added in 3.11, but it can be configured in the
firmware regardless of kernel support.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Tested-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 28 insertions, 0 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index ea2a315df6b7bb..272fc934ce6b9b 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -61,6 +61,8 @@ static int rtc_suspend(struct device *dev)
 	if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
 		return 0;
 
+	rtc->valid_alarm = !rtc_read_alarm(rtc, &rtc->alarm);
+
 	/* snapshot the current RTC and system time at suspend*/
 	err = rtc_read_time(rtc, &tm);
 	if (err < 0) {
@@ -105,6 +107,27 @@ static int rtc_resume(struct device *dev)
 	if (timekeeping_rtc_skipresume())
 		return 0;
 
+	/*
+	 * Ensure that the platform hasn't overwritten a pending alarm while
+	 * suspended
+	 */
+	if (rtc->valid_alarm) {
+		long now, scheduled;
+
+		rtc_read_time(rtc, &tm);
+		rtc_tm_to_time(&rtc->alarm.time, &scheduled);
+		rtc_tm_to_time(&tm, &now);
+
+		/* Clear the alarm registers if it went off during suspend */
+		if (scheduled <= now) {
+			rtc_time_to_tm(0, &rtc->alarm.time);
+			rtc->alarm.enabled = 0;
+		}
+
+		if (rtc->ops && rtc->ops->set_alarm)
+			rtc->ops->set_alarm(rtc->dev.parent, &rtc->alarm);
+	}
+
 	rtc_hctosys_ret = -ENODEV;
 	if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
 		return 0;
@@ -141,6 +164,7 @@ static int rtc_resume(struct device *dev)
 	if (sleep_time.tv_sec >= 0)
 		timekeeping_inject_sleeptime64(&sleep_time);
 	rtc_hctosys_ret = 0;
+
 	return 0;
 }
 
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 8dcf6825fa88bb..c8b68741994e71 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -134,6 +134,10 @@ struct rtc_device
 	/* Some hardware can't support UIE mode */
 	int uie_unsupported;
 
+#ifdef CONFIG_PM_SLEEP
+	struct rtc_wkalrm alarm;
+	bool valid_alarm;
+#endif
 #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
 	struct work_struct uie_task;
 	struct timer_list uie_timer;