diff options
| -rw-r--r-- | drivers/rtc/interface.c | 83 |
1 files changed, 82 insertions, 1 deletions
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index 8adcab3c3653..de0da545c7a1 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) |
