1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index 2ae0e8304d3a..4d27ccc4fc06 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -17,6 +17,13 @@
 
 /* device attributes */
 
+/*
+ * NOTE:  RTC times displayed in sysfs use the RTC's timezone.  That's
+ * ideally UTC.  However, PCs that also boot to MS-Windows normally use
+ * the local time and change to match daylight savings time.  That affects
+ * attributes including date, time, since_epoch, and wakealarm.
+ */
+
 static ssize_t
 rtc_sysfs_show_name(struct device *dev, struct device_attribute *attr,
                 char *buf)
@@ -113,13 +120,13 @@ rtc_sysfs_show_wakealarm(struct device *dev, struct device_attribute *attr,
         unsigned long alarm;
         struct rtc_wkalrm alm;
 
-        /* Don't show disabled alarms; but the RTC could leave the
-         * alarm enabled after it's already triggered.  Alarms are
-         * conceptually one-shot, even though some common hardware
-         * (PCs) doesn't actually work that way.
+        /* Don't show disabled alarms.  For uniformity, RTC alarms are
+         * conceptually one-shot, even though some common RTCs (on PCs)
+         * don't actually work that way.
          *
-         * REVISIT maybe we should require RTC implementations to
-         * disable the RTC alarm after it triggers, for uniformity.
+         * NOTE: RTC implementations where the alarm doesn't match an
+         * exact YYYY-MM-DD HH:MM[:SS] date *must* disable their RTC
+         * alarms after they trigger, to ensure one-shot semantics.
          */
         retval = rtc_read_alarm(to_rtc_device(dev), &alm);
         if (retval == 0 && alm.enabled) {