Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer updates from Thomas Gleixner:
 "The timer department delivers this time:

   - Support for cross clock domain timestamps in the core code plus a
     first user.  That allows more precise timestamping for PTP and
     later for audio and other peripherals.

     The ptp/e1000e patches have been acked by the relevant maintainers
     and are carried in the timer tree to avoid merge ordering issues.

   - Support for unregistering the current clocksource watchdog.  That
     lifts a limitation for switching clocksources which has been there
     from day 1

   - The usual pile of fixes and updates to the core and the drivers.
     Nothing outstanding and exciting"

* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (26 commits)
  time/timekeeping: Work around false positive GCC warning
  e1000e: Adds hardware supported cross timestamp on e1000e nic
  ptp: Add PTP_SYS_OFFSET_PRECISE for driver crosstimestamping
  x86/tsc: Always Running Timer (ART) correlated clocksource
  hrtimer: Revert CLOCK_MONOTONIC_RAW support
  time: Add history to cross timestamp interface supporting slower devices
  time: Add driver cross timestamp interface for higher precision time synchronization
  time: Remove duplicated code in ktime_get_raw_and_real()
  time: Add timekeeping snapshot code capturing system time and counter
  time: Add cycles to nanoseconds translation
  jiffies: Use CLOCKSOURCE_MASK instead of constant
  clocksource: Introduce clocksource_freq2mult()
  clockevents/drivers/exynos_mct: Implement ->set_state_oneshot_stopped()
  clockevents/drivers/arm_global_timer: Implement ->set_state_oneshot_stopped()
  clockevents/drivers/arm_arch_timer: Implement ->set_state_oneshot_stopped()
  clocksource/drivers/arm_global_timer: Register delay timer
  clocksource/drivers/lpc32xx: Support timer-based ARM delay
  clocksource/drivers/lpc32xx: Support periodic mode
  clocksource/drivers/lpc32xx: Don't use the prescaler counter for clockevents
  clocksource/drivers/rockchip: Add err handle for rk_timer_init
  ...

1 files changed, 42 insertions, 10 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 664de539299b..56ece145a814 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -323,13 +323,42 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 		/* cs is a watchdog. */
 		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+	}
+	spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
+static void clocksource_select_watchdog(bool fallback)
+{
+	struct clocksource *cs, *old_wd;
+	unsigned long flags;
+
+	spin_lock_irqsave(&watchdog_lock, flags);
+	/* save current watchdog */
+	old_wd = watchdog;
+	if (fallback)
+		watchdog = NULL;
+
+	list_for_each_entry(cs, &clocksource_list, list) {
+		/* cs is a clocksource to be watched. */
+		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
+			continue;
+
+		/* Skip current if we were requested for a fallback. */
+		if (fallback && cs == old_wd)
+			continue;
+
 		/* Pick the best watchdog. */
-		if (!watchdog || cs->rating > watchdog->rating) {
+		if (!watchdog || cs->rating > watchdog->rating)
 			watchdog = cs;
-			/* Reset watchdog cycles */
-			clocksource_reset_watchdog();
-		}
 	}
+	/* If we failed to find a fallback restore the old one. */
+	if (!watchdog)
+		watchdog = old_wd;
+
+	/* If we changed the watchdog we need to reset cycles. */
+	if (watchdog != old_wd)
+		clocksource_reset_watchdog();
+
 	/* Check if the watchdog timer needs to be started. */
 	clocksource_start_watchdog();
 	spin_unlock_irqrestore(&watchdog_lock, flags);
@@ -404,6 +433,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 }
 
+static void clocksource_select_watchdog(bool fallback) { }
 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 static inline void clocksource_resume_watchdog(void) { }
 static inline int __clocksource_watchdog_kthread(void) { return 0; }
@@ -736,6 +766,7 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
 	clocksource_enqueue(cs);
 	clocksource_enqueue_watchdog(cs);
 	clocksource_select();
+	clocksource_select_watchdog(false);
 	mutex_unlock(&clocksource_mutex);
 	return 0;
 }
@@ -758,6 +789,7 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
 	mutex_lock(&clocksource_mutex);
 	__clocksource_change_rating(cs, rating);
 	clocksource_select();
+	clocksource_select_watchdog(false);
 	mutex_unlock(&clocksource_mutex);
 }
 EXPORT_SYMBOL(clocksource_change_rating);
@@ -767,12 +799,12 @@ EXPORT_SYMBOL(clocksource_change_rating);
  */
 static int clocksource_unbind(struct clocksource *cs)
 {
-	/*
-	 * I really can't convince myself to support this on hardware
-	 * designed by lobotomized monkeys.
-	 */
-	if (clocksource_is_watchdog(cs))
-		return -EBUSY;
+	if (clocksource_is_watchdog(cs)) {
+		/* Select and try to install a replacement watchdog. */
+		clocksource_select_watchdog(true);
+		if (clocksource_is_watchdog(cs))
+			return -EBUSY;
+	}
 
 	if (cs == curr_clocksource) {
 		/* Select and try to install a replacement clock source */