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>

arch/s390/include/asm/cio.h

@@ -372,6 +372,7 @@ struct gen_pool *cio_gp_dma_create(struct device *dma_dev, int nr_pages);
 /* Function from drivers/s390/cio/chsc.c */
 int chsc_sstpc(void *page, unsigned int op, u16 ctrl, u64 *clock_delta);
 int chsc_sstpi(void *page, void *result, size_t size);
+int chsc_stzi(void *page, void *result, size_t size);
 int chsc_sgib(u32 origin);
 
 #endif

arch/s390/include/asm/stp.h

@@ -25,7 +25,9 @@ struct stp_irq_parm {
 
 struct stp_sstpi {
 	u32		: 32;
-	u32		:  8;
+	u32 tu		:  1;
+	u32 lu		:  1;
+	u32		:  6;
 	u32 stratum	:  8;
 	u32 vbits	: 16;
 	u32 leaps	: 16;
@@ -46,6 +48,48 @@ struct stp_sstpi {
 	u32 rsvd[48];
 } __packed;
 
+struct stp_tzib {
+	u32 tzan	: 16;
+	u32		: 16;
+	u32 tzo		: 16;
+	u32 dsto	: 16;
+	u32 stn;
+	u32 dstn;
+	u64 dst_on_alg;
+	u64 dst_off_alg;
+} __packed;
+
+struct stp_tcpib {
+	u32 atcode	: 4;
+	u32 ntcode	: 4;
+	u32 d		: 1;
+	u32		: 23;
+	s32 tto;
+	struct stp_tzib atzib;
+	struct stp_tzib ntzib;
+	s32 adst_offset : 16;
+	s32 ndst_offset : 16;
+	u32 rsvd1;
+	u64 ntzib_update;
+	u64 ndsto_update;
+} __packed;
+
+struct stp_lsoib {
+	u32 p		: 1;
+	u32		: 31;
+	s32 also	: 16;
+	s32 nlso	: 16;
+	u64 nlsout;
+} __packed;
+
+struct stp_stzi {
+	u32 rsvd0[3];
+	u64 data_ts;
+	u32 rsvd1[22];
+	struct stp_tcpib tcpib;
+	struct stp_lsoib lsoib;
+} __packed;
+
 /* Functions needed by the machine check handler */
 int stp_sync_check(void);
 int stp_island_check(void);

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;
-
+	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);

drivers/s390/cio/chsc.c

@@ -1260,6 +1260,27 @@ int chsc_sstpi(void *page, void *result, size_t size)
 	return (rr->response.code == 0x0001) ? 0 : -EIO;
 }
 
+int chsc_stzi(void *page, void *result, size_t size)
+{
+	struct {
+		struct chsc_header request;
+		unsigned int rsvd0[3];
+		struct chsc_header response;
+		char data[];
+	} *rr;
+	int rc;
+
+	memset(page, 0, PAGE_SIZE);
+	rr = page;
+	rr->request.length = 0x0010;
+	rr->request.code = 0x003e;
+	rc = chsc(rr);
+	if (rc)
+		return -EIO;
+	memcpy(result, &rr->data, size);
+	return (rr->response.code == 0x0001) ? 0 : -EIO;
+}
+
 int chsc_siosl(struct subchannel_id schid)
 {
 	struct {