s390/stp: add support for leap seconds

In the current implementation, leap seconds are only synchronized
during the bootup process when the STP clock is synced. If the Leap
second offset (LSO) changes the machine must be rebooted, which is
not desired. This patch adds the required code to handle Leap second
changes during runtime. If the Leap second changes, a Configuration
change machine check is triggered. The STP code than schedules a Leap
second insertion/deletion with do_adjtimex().

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 85 insertions, 9 deletions

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index bee380340bad..49648d574b35 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -598,6 +598,81 @@ static int stp_sync_clock(void *data)
 	return 0;
 }
 
+static int stp_clear_leap(void)
+{
+	struct __kernel_timex txc;
+	int ret;
+
+	memset(&txc, 0, sizeof(txc));
+
+	ret = do_adjtimex(&txc);
+	if (ret < 0)
+		return ret;
+
+	txc.modes = ADJ_STATUS;
+	txc.status &= ~(STA_INS|STA_DEL);
+	return do_adjtimex(&txc);
+}
+
+static void stp_check_leap(void)
+{
+	struct stp_stzi stzi;
+	struct stp_lsoib *lsoib = &stzi.lsoib;
+	struct __kernel_timex txc;
+	int64_t timediff;
+	int leapdiff, ret;
+
+	if (!stp_info.lu || !check_sync_clock()) {
+		/*
+		 * Either a scheduled leap second was removed by the operator,
+		 * or STP is out of sync. In both cases, clear the leap second
+		 * kernel flags.
+		 */
+		if (stp_clear_leap() < 0)
+			pr_err("failed to clear leap second flags\n");
+		return;
+	}
+
+	if (chsc_stzi(stp_page, &stzi, sizeof(stzi))) {
+		pr_err("stzi failed\n");
+		return;
+	}
+
+	timediff = tod_to_ns(lsoib->nlsout - get_tod_clock()) / NSEC_PER_SEC;
+	leapdiff = lsoib->nlso - lsoib->also;
+
+	if (leapdiff != 1 && leapdiff != -1) {
+		pr_err("Cannot schedule %d leap seconds\n", leapdiff);
+		return;
+	}
+
+	if (timediff < 0) {
+		if (stp_clear_leap() < 0)
+			pr_err("failed to clear leap second flags\n");
+	} else if (timediff < 7200) {
+		memset(&txc, 0, sizeof(txc));
+		ret = do_adjtimex(&txc);
+		if (ret < 0)
+			return;
+
+		txc.modes = ADJ_STATUS;
+		if (leapdiff > 0)
+			txc.status |= STA_INS;
+		else
+			txc.status |= STA_DEL;
+		ret = do_adjtimex(&txc);
+		if (ret < 0)
+			pr_err("failed to set leap second flags\n");
+		/* arm Timer to clear leap second flags */
+		mod_timer(&stp_timer, jiffies + msecs_to_jiffies(14400 * MSEC_PER_SEC));
+	} else {
+		/* The day the leap second is scheduled for hasn't been reached. Retry
+		 * in one hour.
+		 */
+		mod_timer(&stp_timer, jiffies + msecs_to_jiffies(3600 * MSEC_PER_SEC));
+	}
+}
+
 /*
  * STP work. Check for the STP state and take over the clock
  * synchronization if the STP clock source is usable.
@@ -616,7 +691,7 @@ static void stp_work_fn(struct work_struct *work)
 		goto out_unlock;
 	}
 
-	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xb0e0, NULL);
+	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xf0e0, NULL);
 	if (rc)
 		goto out_unlock;
 
@@ -625,14 +700,13 @@ static void stp_work_fn(struct work_struct *work)
 		goto out_unlock;
 
 	/* Skip synchronization if the clock is already in sync. */
-	if (check_sync_clock())
-		goto out_unlock;
-
-	memset(&stp_sync, 0, sizeof(stp_sync));
-	cpus_read_lock();
-	atomic_set(&stp_sync.cpus, num_online_cpus() - 1);
-	stop_machine_cpuslocked(stp_sync_clock, &stp_sync, cpu_online_mask);
-	cpus_read_unlock();
+	if (!check_sync_clock()) {
+		memset(&stp_sync, 0, sizeof(stp_sync));
+		cpus_read_lock();
+		atomic_set(&stp_sync.cpus, num_online_cpus() - 1);
+		stop_machine_cpuslocked(stp_sync_clock, &stp_sync, cpu_online_mask);
+		cpus_read_unlock();
+	}
 
 	if (!check_sync_clock())
 		/*
@@ -640,6 +714,8 @@ static void stp_work_fn(struct work_struct *work)
 		 * Retry after a second.
 		 */
 		mod_timer(&stp_timer, jiffies + msecs_to_jiffies(MSEC_PER_SEC));
+	else if (stp_info.lu)
+		stp_check_leap();
 
 out_unlock:
 	mutex_unlock(&stp_work_mutex);