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path: root/drivers/rtc/interface.c
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-rw-r--r--drivers/rtc/interface.c83
1 files changed, 82 insertions, 1 deletions
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 8adcab3c365..de0da545c7a 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -100,7 +100,7 @@ int rtc_set_mmss(struct rtc_device *rtc, unsigned long secs)
}
EXPORT_SYMBOL_GPL(rtc_set_mmss);
-int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
+static int rtc_read_alarm_internal(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
{
int err;
@@ -120,6 +120,87 @@ int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
mutex_unlock(&rtc->ops_lock);
return err;
}
+
+int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
+{
+ int err;
+ struct rtc_time before, now;
+ int first_time = 1;
+
+ /* The lower level RTC driver may not be capable of filling
+ * in all fields of the rtc_time struct (eg. rtc-cmos),
+ * and so might instead return -1 in some fields.
+ * We deal with that here by grabbing a current RTC timestamp
+ * and using values from that for any missing (-1) values.
+ *
+ * But this can be racey, because some fields of the RTC timestamp
+ * may have wrapped in the interval since we read the RTC alarm,
+ * which would lead to us inserting inconsistent values in place
+ * of the -1 fields.
+ *
+ * Reading the alarm and timestamp in the reverse sequence
+ * would have the same race condition, and not solve the issue.
+ *
+ * So, we must first read the RTC timestamp,
+ * then read the RTC alarm value,
+ * and then read a second RTC timestamp.
+ *
+ * If any fields of the second timestamp have changed
+ * when compared with the first timestamp, then we know
+ * our timestamp may be inconsistent with that used by
+ * the low-level rtc_read_alarm_internal() function.
+ *
+ * So, when the two timestamps disagree, we just loop and do
+ * the process again to get a fully consistent set of values.
+ *
+ * This could all instead be done in the lower level driver,
+ * but since more than one lower level RTC implementation needs it,
+ * then it's probably best best to do it here instead of there..
+ */
+
+ /* Get the "before" timestamp */
+ err = rtc_read_time(rtc, &before);
+ if (err < 0)
+ return err;
+ do {
+ if (!first_time)
+ memcpy(&before, &now, sizeof(struct rtc_time));
+ first_time = 0;
+
+ /* get the RTC alarm values, which may be incomplete */
+ err = rtc_read_alarm_internal(rtc, alarm);
+ if (err)
+ return err;
+ if (!alarm->enabled)
+ return 0;
+
+ /* get the "after" timestamp, to detect wrapped fields */
+ err = rtc_read_time(rtc, &now);
+ if (err < 0)
+ return err;
+
+ /* note that tm_sec is a "don't care" value here: */
+ } while ( before.tm_min != now.tm_min
+ || before.tm_hour != now.tm_hour
+ || before.tm_mon != now.tm_mon
+ || before.tm_year != now.tm_year
+ || before.tm_isdst != now.tm_isdst);
+
+ /* Fill in any missing alarm fields using the timestamp */
+ if (alarm->time.tm_sec == -1)
+ alarm->time.tm_sec = now.tm_sec;
+ if (alarm->time.tm_min == -1)
+ alarm->time.tm_min = now.tm_min;
+ if (alarm->time.tm_hour == -1)
+ alarm->time.tm_hour = now.tm_hour;
+ if (alarm->time.tm_mday == -1)
+ alarm->time.tm_mday = now.tm_mday;
+ if (alarm->time.tm_mon == -1)
+ alarm->time.tm_mon = now.tm_mon;
+ if (alarm->time.tm_year == -1)
+ alarm->time.tm_year = now.tm_year;
+ return 0;
+}
EXPORT_SYMBOL_GPL(rtc_read_alarm);
int rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)