Let kernel synchronize RTC to system clock.

Reset the STA_UNSYNC flag and maxerror value with every frequency update
to let the kernel synchronize the RTC to the system clock (11 minute mode).

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>

clock.c

@@ -1070,6 +1070,8 @@ enum servo_state clock_synchronize(struct clock *c,
 		break;
 	case SERVO_LOCKED:
 		clockadj_set_freq(c->clkid, -adj);
+		if (c->clkid == CLOCK_REALTIME)
+			sysclk_set_sync();
 		break;
 	}
 	return state;

clockadj.c

@@ -25,6 +25,8 @@
 
 #define NS_PER_SEC 1000000000LL
 
+static int realtime_leap_bit;
+
 void clockadj_set_freq(clockid_t clkid, double freq)
 {
 	struct timex tx;
@@ -94,6 +96,7 @@ void sysclk_set_leap(int leap)
 		pr_err("failed to set the clock status: %m");
 	else if (m)
 		pr_notice(m);
+	realtime_leap_bit = tx.status;
 }
 
 int sysclk_max_freq(void)
@@ -110,3 +113,17 @@ int sysclk_max_freq(void)
 		f = 500000;
 	return f;
 }
+
+void sysclk_set_sync(void)
+{
+	clockid_t clkid = CLOCK_REALTIME;
+	struct timex tx;
+	memset(&tx, 0, sizeof(tx));
+	/* Clear the STA_UNSYNC flag from the status and keep the maxerror
+	   value (which is increased automatically by 500 ppm) below 16 seconds
+	   to avoid getting the STA_UNSYNC flag back. */
+	tx.modes = ADJ_STATUS | ADJ_MAXERROR;
+	tx.status = realtime_leap_bit;
+	if (clock_adjtime(clkid, &tx) < 0)
+		pr_err("failed to set clock status and maximum error: %m");
+}

clockadj.h

@@ -57,4 +57,9 @@ void sysclk_set_leap(int leap);
  */
 int sysclk_max_freq(void);
 
+/**
+ * Mark the system clock as synchronized to let the kernel synchronize
+ * the real-time clock (RTC) to it.
+ */
+void sysclk_set_sync(void);
 #endif

phc2sys.c

@@ -187,6 +187,8 @@ static void update_clock(struct clock *clock,
 		/* Fall through. */
 	case SERVO_LOCKED:
 		clockadj_set_freq(clock->clkid, -ppb);
+		if (clock->clkid == CLOCK_REALTIME)
+			sysclk_set_sync();
 		break;
 	}