s390/time: STP sync clock correction

The sync clock operation of the channel subsystem call for STP delivers
the TOD clock difference as a result. Use this TOD clock difference
instead of the difference between the TOD timestamps before and after
the sync clock operation.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/cio.h

@@ -320,7 +320,7 @@ struct cio_iplinfo {
 extern int cio_get_iplinfo(struct cio_iplinfo *iplinfo);
 
 /* Function from drivers/s390/cio/chsc.c */
-int chsc_sstpc(void *page, unsigned int op, u16 ctrl);
+int chsc_sstpc(void *page, unsigned int op, u16 ctrl, u64 *clock_delta);
 int chsc_sstpi(void *page, void *result, size_t size);
 
 #endif

arch/s390/kernel/time.c

@@ -1455,7 +1455,7 @@ static void __init stp_reset(void)
 	int rc;
 
 	stp_page = (void *) get_zeroed_page(GFP_ATOMIC);
-	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000);
+	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000, NULL);
 	if (rc == 0)
 		set_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags);
 	else if (stp_online) {
@@ -1554,11 +1554,10 @@ static int stp_sync_clock(void *data)
 	    stp_info.todoff[2] || stp_info.todoff[3] ||
 	    stp_info.tmd != 2) {
 		old_clock = get_tod_clock();
-		rc = chsc_sstpc(stp_page, STP_OP_SYNC, 0);
+		rc = chsc_sstpc(stp_page, STP_OP_SYNC, 0, &clock_delta);
 		if (rc == 0) {
-			new_clock = get_tod_clock();
+			new_clock = old_clock + clock_delta;
 			delta = adjust_time(old_clock, new_clock, 0);
-			clock_delta = new_clock - old_clock;
 			atomic_notifier_call_chain(&s390_epoch_delta_notifier,
 						   0, &clock_delta);
 			fixup_clock_comparator(delta);
@@ -1590,12 +1589,12 @@ static void stp_work_fn(struct work_struct *work)
 	mutex_lock(&stp_work_mutex);
 
 	if (!stp_online) {
-		chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000);
+		chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000, NULL);
 		del_timer_sync(&stp_timer);
 		goto out_unlock;
 	}
 
-	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xb0e0);
+	rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xb0e0, NULL);
 	if (rc)
 		goto out_unlock;
 

drivers/s390/cio/chsc.c

@@ -1176,7 +1176,7 @@ chsc_determine_css_characteristics(void)
 EXPORT_SYMBOL_GPL(css_general_characteristics);
 EXPORT_SYMBOL_GPL(css_chsc_characteristics);
 
-int chsc_sstpc(void *page, unsigned int op, u16 ctrl)
+int chsc_sstpc(void *page, unsigned int op, u16 ctrl, u64 *clock_delta)
 {
 	struct {
 		struct chsc_header request;
@@ -1186,7 +1186,9 @@ int chsc_sstpc(void *page, unsigned int op, u16 ctrl)
 		unsigned int ctrl : 16;
 		unsigned int rsvd2[5];
 		struct chsc_header response;
-		unsigned int rsvd3[7];
+		unsigned int rsvd3[3];
+		u64 clock_delta;
+		unsigned int rsvd4[2];
 	} __attribute__ ((packed)) *rr;
 	int rc;
 
@@ -1200,6 +1202,8 @@ int chsc_sstpc(void *page, unsigned int op, u16 ctrl)
 	if (rc)
 		return -EIO;
 	rc = (rr->response.code == 0x0001) ? 0 : -EIO;
+	if (clock_delta)
+		*clock_delta = rr->clock_delta;
 	return rc;
 }