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path: root/drivers/rtc/rtc-sysfs.c
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Diffstat (limited to 'drivers/rtc/rtc-sysfs.c')
-rw-r--r--drivers/rtc/rtc-sysfs.c19
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) {