From 4929d50a3f7e3d4b6ca29f9997f18fdfdb239924 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Mon, 8 Apr 2013 15:44:10 +0200
Subject: [PATCH] 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    |  2 ++
 clockadj.c | 17 +++++++++++++++++
 clockadj.h |  5 +++++
 phc2sys.c  |  2 ++
 4 files changed, 26 insertions(+)

diff --git a/clock.c b/clock.c
index cc692e9..eceedc5 100644
--- a/clock.c
+++ b/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;
diff --git a/clockadj.c b/clockadj.c
index 74963c8..b0505b7 100644
--- a/clockadj.c
+++ b/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");
+}
diff --git a/clockadj.h b/clockadj.h
index 3779f03..79ae80d 100644
--- a/clockadj.h
+++ b/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
diff --git a/phc2sys.c b/phc2sys.c
index 076840c..93495a4 100644
--- a/phc2sys.c
+++ b/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;
 	}