9 files changed, 848 insertions, 372 deletions

diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 0b0a6366c9d4..ee266620b06c 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -1,4 +1,4 @@
-obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o timecompare.o
+obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o timecompare.o timeconv.o
 
 obj-$(CONFIG_GENERIC_CLOCKEVENTS_BUILD)         += clockevents.o
 obj-$(CONFIG_GENERIC_CLOCKEVENTS)               += tick-common.o
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7466cb811251..5e18c6ab2c6a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -21,7 +21,6 @@
  *
  * TODO WishList:
  *   o Allow clocksource drivers to be unregistered
- *   o get rid of clocksource_jiffies extern
  */
 
 #include <linux/clocksource.h>
@@ -30,6 +29,7 @@
 #include <linux/module.h>
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>
+#include <linux/kthread.h>
 
 void timecounter_init(struct timecounter *tc,
                       const struct cyclecounter *cc,
@@ -107,50 +107,35 @@ u64 timecounter_cyc2time(struct timecounter *tc,
 }
 EXPORT_SYMBOL(timecounter_cyc2time);
 
-/* XXX - Would like a better way for initializing curr_clocksource */
-extern struct clocksource clocksource_jiffies;
-
 /*[Clocksource internal variables]---------
  * curr_clocksource:
- *      currently selected clocksource. Initialized to clocksource_jiffies.
- * next_clocksource:
- *      pending next selected clocksource.
+ *      currently selected clocksource.
  * clocksource_list:
  *      linked list with the registered clocksources
- * clocksource_lock:
- *      protects manipulations to curr_clocksource and next_clocksource
- *      and the clocksource_list
+ * clocksource_mutex:
+ *      protects manipulations to curr_clocksource and the clocksource_list
  * override_name:
  *      Name of the user-specified clocksource.
  */
-static struct clocksource *curr_clocksource = &clocksource_jiffies;
-static struct clocksource *next_clocksource;
-static struct clocksource *clocksource_override;
+static struct clocksource *curr_clocksource;
 static LIST_HEAD(clocksource_list);
-static DEFINE_SPINLOCK(clocksource_lock);
+static DEFINE_MUTEX(clocksource_mutex);
 static char override_name[32];
 static int finished_booting;
 
-/* clocksource_done_booting - Called near the end of core bootup
- *
- * Hack to avoid lots of clocksource churn at boot time.
- * We use fs_initcall because we want this to start before
- * device_initcall but after subsys_initcall.
- */
-static int __init clocksource_done_booting(void)
-{
-        finished_booting = 1;
-        return 0;
-}
-fs_initcall(clocksource_done_booting);
-
 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
+static void clocksource_watchdog_work(struct work_struct *work);
+
 static LIST_HEAD(watchdog_list);
 static struct clocksource *watchdog;
 static struct timer_list watchdog_timer;
+static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
 static DEFINE_SPINLOCK(watchdog_lock);
 static cycle_t watchdog_last;
-static unsigned long watchdog_resumed;
+static int watchdog_running;
+
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
 
 /*
  * Interval: 0.5sec Threshold: 0.0625s
@@ -158,135 +143,249 @@ static unsigned long watchdog_resumed;
 #define WATCHDOG_INTERVAL (HZ >> 1)
 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
 
-static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
+static void clocksource_watchdog_work(struct work_struct *work)
 {
-        if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
-                return;
+        /*
+         * If kthread_run fails the next watchdog scan over the
+         * watchdog_list will find the unstable clock again.
+         */
+        kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
+}
+
+static void __clocksource_unstable(struct clocksource *cs)
+{
+        cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
+        cs->flags |= CLOCK_SOURCE_UNSTABLE;
+        if (finished_booting)
+                schedule_work(&watchdog_work);
+}
 
+static void clocksource_unstable(struct clocksource *cs, int64_t delta)
+{
         printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
                cs->name, delta);
-        cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
-        clocksource_change_rating(cs, 0);
-        list_del(&cs->wd_list);
+        __clocksource_unstable(cs);
+}
+
+/**
+ * clocksource_mark_unstable - mark clocksource unstable via watchdog
+ * @cs:         clocksource to be marked unstable
+ *
+ * This function is called instead of clocksource_change_rating from
+ * cpu hotplug code to avoid a deadlock between the clocksource mutex
+ * and the cpu hotplug mutex. It defers the update of the clocksource
+ * to the watchdog thread.
+ */
+void clocksource_mark_unstable(struct clocksource *cs)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
+                if (list_empty(&cs->wd_list))
+                        list_add(&cs->wd_list, &watchdog_list);
+                __clocksource_unstable(cs);
+        }
+        spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
 static void clocksource_watchdog(unsigned long data)
 {
-        struct clocksource *cs, *tmp;
+        struct clocksource *cs;
         cycle_t csnow, wdnow;
         int64_t wd_nsec, cs_nsec;
-        int resumed;
+        int next_cpu;
 
         spin_lock(&watchdog_lock);
-
-        resumed = test_and_clear_bit(0, &watchdog_resumed);
+        if (!watchdog_running)
+                goto out;
 
         wdnow = watchdog->read(watchdog);
-        wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
+        wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
+                                     watchdog->mult, watchdog->shift);
         watchdog_last = wdnow;
 
-        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
-                csnow = cs->read(cs);
+        list_for_each_entry(cs, &watchdog_list, wd_list) {
 
-                if (unlikely(resumed)) {
-                        cs->wd_last = csnow;
+                /* Clocksource already marked unstable? */
+                if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+                        if (finished_booting)
+                                schedule_work(&watchdog_work);
                         continue;
                 }
 
-                /* Initialized ? */
+                csnow = cs->read(cs);
+
+                /* Clocksource initialized ? */
                 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
-                        if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
-                            (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
-                                cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
-                                /*
-                                 * We just marked the clocksource as
-                                 * highres-capable, notify the rest of the
-                                 * system as well so that we transition
-                                 * into high-res mode:
-                                 */
-                                tick_clock_notify();
-                        }
                         cs->flags |= CLOCK_SOURCE_WATCHDOG;
                         cs->wd_last = csnow;
-                } else {
-                        cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
-                        cs->wd_last = csnow;
-                        /* Check the delta. Might remove from the list ! */
-                        clocksource_ratewd(cs, cs_nsec - wd_nsec);
+                        continue;
                 }
-        }
 
-        if (!list_empty(&watchdog_list)) {
-                /*
-                 * Cycle through CPUs to check if the CPUs stay
-                 * synchronized to each other.
-                 */
-                int next_cpu = cpumask_next(raw_smp_processor_id(),
-                                            cpu_online_mask);
+                /* Check the deviation from the watchdog clocksource. */
+                cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
+                                             cs->mask, cs->mult, cs->shift);
+                cs->wd_last = csnow;
+                if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
+                        clocksource_unstable(cs, cs_nsec - wd_nsec);
+                        continue;
+                }
 
-                if (next_cpu >= nr_cpu_ids)
-                        next_cpu = cpumask_first(cpu_online_mask);
-                watchdog_timer.expires += WATCHDOG_INTERVAL;
-                add_timer_on(&watchdog_timer, next_cpu);
+                if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
+                    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
+                    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
+                        cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+                        /*
+                         * We just marked the clocksource as highres-capable,
+                         * notify the rest of the system as well so that we
+                         * transition into high-res mode:
+                         */
+                        tick_clock_notify();
+                }
         }
+
+        /*
+         * Cycle through CPUs to check if the CPUs stay synchronized
+         * to each other.
+         */
+        next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+        if (next_cpu >= nr_cpu_ids)
+                next_cpu = cpumask_first(cpu_online_mask);
+        watchdog_timer.expires += WATCHDOG_INTERVAL;
+        add_timer_on(&watchdog_timer, next_cpu);
+out:
         spin_unlock(&watchdog_lock);
 }
+
+static inline void clocksource_start_watchdog(void)
+{
+        if (watchdog_running || !watchdog || list_empty(&watchdog_list))
+                return;
+        init_timer(&watchdog_timer);
+        watchdog_timer.function = clocksource_watchdog;
+        watchdog_last = watchdog->read(watchdog);
+        watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
+        add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
+        watchdog_running = 1;
+}
+
+static inline void clocksource_stop_watchdog(void)
+{
+        if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
+                return;
+        del_timer(&watchdog_timer);
+        watchdog_running = 0;
+}
+
+static inline void clocksource_reset_watchdog(void)
+{
+        struct clocksource *cs;
+
+        list_for_each_entry(cs, &watchdog_list, wd_list)
+                cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
+}
+
 static void clocksource_resume_watchdog(void)
 {
-        set_bit(0, &watchdog_resumed);
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        clocksource_reset_watchdog();
+        spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
-static void clocksource_check_watchdog(struct clocksource *cs)
+static void clocksource_enqueue_watchdog(struct clocksource *cs)
 {
-        struct clocksource *cse;
         unsigned long flags;
 
         spin_lock_irqsave(&watchdog_lock, flags);
         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
-                int started = !list_empty(&watchdog_list);
-
+                /* cs is a clocksource to be watched. */
                 list_add(&cs->wd_list, &watchdog_list);
-                if (!started && watchdog) {
-                        watchdog_last = watchdog->read(watchdog);
-                        watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
-                        add_timer_on(&watchdog_timer,
-                                     cpumask_first(cpu_online_mask));
-                }
+                cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
         } else {
+                /* cs is a watchdog. */
                 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
                         cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
-
+                /* Pick the best watchdog. */
                 if (!watchdog || cs->rating > watchdog->rating) {
-                        if (watchdog)
-                                del_timer(&watchdog_timer);
                         watchdog = cs;
-                        init_timer(&watchdog_timer);
-                        watchdog_timer.function = clocksource_watchdog;
-
                         /* Reset watchdog cycles */
-                        list_for_each_entry(cse, &watchdog_list, wd_list)
-                                cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
-                        /* Start if list is not empty */
-                        if (!list_empty(&watchdog_list)) {
-                                watchdog_last = watchdog->read(watchdog);
-                                watchdog_timer.expires =
-                                        jiffies + WATCHDOG_INTERVAL;
-                                add_timer_on(&watchdog_timer,
-                                             cpumask_first(cpu_online_mask));
-                        }
+                        clocksource_reset_watchdog();
+                }
+        }
+        /* Check if the watchdog timer needs to be started. */
+        clocksource_start_watchdog();
+        spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
+static void clocksource_dequeue_watchdog(struct clocksource *cs)
+{
+        struct clocksource *tmp;
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+                /* cs is a watched clocksource. */
+                list_del_init(&cs->wd_list);
+        } else if (cs == watchdog) {
+                /* Reset watchdog cycles */
+                clocksource_reset_watchdog();
+                /* Current watchdog is removed. Find an alternative. */
+                watchdog = NULL;
+                list_for_each_entry(tmp, &clocksource_list, list) {
+                        if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
+                                continue;
+                        if (!watchdog || tmp->rating > watchdog->rating)
+                                watchdog = tmp;
                 }
         }
+        cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
+        /* Check if the watchdog timer needs to be stopped. */
+        clocksource_stop_watchdog();
         spin_unlock_irqrestore(&watchdog_lock, flags);
 }
-#else
-static void clocksource_check_watchdog(struct clocksource *cs)
+
+static int clocksource_watchdog_kthread(void *data)
+{
+        struct clocksource *cs, *tmp;
+        unsigned long flags;
+        LIST_HEAD(unstable);
+
+        mutex_lock(&clocksource_mutex);
+        spin_lock_irqsave(&watchdog_lock, flags);
+        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
+                if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+                        list_del_init(&cs->wd_list);
+                        list_add(&cs->wd_list, &unstable);
+                }
+        /* Check if the watchdog timer needs to be stopped. */
+        clocksource_stop_watchdog();
+        spin_unlock_irqrestore(&watchdog_lock, flags);
+
+        /* Needs to be done outside of watchdog lock */
+        list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
+                list_del_init(&cs->wd_list);
+                __clocksource_change_rating(cs, 0);
+        }
+        mutex_unlock(&clocksource_mutex);
+        return 0;
+}
+
+#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
+
+static void clocksource_enqueue_watchdog(struct clocksource *cs)
 {
         if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 }
 
+static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 static inline void clocksource_resume_watchdog(void) { }
-#endif
+static inline int clocksource_watchdog_kthread(void *data) { return 0; }
+
+#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
 /**
  * clocksource_resume - resume the clocksource(s)
@@ -294,18 +393,12 @@ static inline void clocksource_resume_watchdog(void) { }
 void clocksource_resume(void)
 {
         struct clocksource *cs;
-        unsigned long flags;
 
-        spin_lock_irqsave(&clocksource_lock, flags);
-
-        list_for_each_entry(cs, &clocksource_list, list) {
+        list_for_each_entry(cs, &clocksource_list, list)
                 if (cs->resume)
                         cs->resume();
-        }
 
         clocksource_resume_watchdog();
-
-        spin_unlock_irqrestore(&clocksource_lock, flags);
 }
 
 /**
@@ -320,75 +413,94 @@ void clocksource_touch_watchdog(void)
         clocksource_resume_watchdog();
 }
 
+#ifdef CONFIG_GENERIC_TIME
+
 /**
- * clocksource_get_next - Returns the selected clocksource
+ * clocksource_select - Select the best clocksource available
  *
+ * Private function. Must hold clocksource_mutex when called.
+ *
+ * Select the clocksource with the best rating, or the clocksource,
+ * which is selected by userspace override.
  */
-struct clocksource *clocksource_get_next(void)
+static void clocksource_select(void)
 {
-        unsigned long flags;
+        struct clocksource *best, *cs;
 
-        spin_lock_irqsave(&clocksource_lock, flags);
-        if (next_clocksource && finished_booting) {
-                curr_clocksource = next_clocksource;
-                next_clocksource = NULL;
+        if (!finished_booting || list_empty(&clocksource_list))
+                return;
+        /* First clocksource on the list has the best rating. */
+        best = list_first_entry(&clocksource_list, struct clocksource, list);
+        /* Check for the override clocksource. */
+        list_for_each_entry(cs, &clocksource_list, list) {
+                if (strcmp(cs->name, override_name) != 0)
+                        continue;
+                /*
+                 * Check to make sure we don't switch to a non-highres
+                 * capable clocksource if the tick code is in oneshot
+                 * mode (highres or nohz)
+                 */
+                if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
+                    tick_oneshot_mode_active()) {
+                        /* Override clocksource cannot be used. */
+                        printk(KERN_WARNING "Override clocksource %s is not "
+                               "HRT compatible. Cannot switch while in "
+                               "HRT/NOHZ mode\n", cs->name);
+                        override_name[0] = 0;
+                } else
+                        /* Override clocksource can be used. */
+                        best = cs;
+                break;
+        }
+        if (curr_clocksource != best) {
+                printk(KERN_INFO "Switching to clocksource %s\n", best->name);
+                curr_clocksource = best;
+                timekeeping_notify(curr_clocksource);
         }
-        spin_unlock_irqrestore(&clocksource_lock, flags);
-
-        return curr_clocksource;
 }
 
-/**
- * select_clocksource - Selects the best registered clocksource.
- *
- * Private function. Must hold clocksource_lock when called.
+#else /* CONFIG_GENERIC_TIME */
+
+static inline void clocksource_select(void) { }
+
+#endif
+
+/*
+ * clocksource_done_booting - Called near the end of core bootup
  *
- * Select the clocksource with the best rating, or the clocksource,
- * which is selected by userspace override.
+ * Hack to avoid lots of clocksource churn at boot time.
+ * We use fs_initcall because we want this to start before
+ * device_initcall but after subsys_initcall.
  */
-static struct clocksource *select_clocksource(void)
+static int __init clocksource_done_booting(void)
 {
-        struct clocksource *next;
-
-        if (list_empty(&clocksource_list))
-                return NULL;
-
-        if (clocksource_override)
-                next = clocksource_override;
-        else
-                next = list_entry(clocksource_list.next, struct clocksource,
-                                  list);
+        finished_booting = 1;
 
-        if (next == curr_clocksource)
-                return NULL;
+        /*
+         * Run the watchdog first to eliminate unstable clock sources
+         */
+        clocksource_watchdog_kthread(NULL);
 
-        return next;
+        mutex_lock(&clocksource_mutex);
+        clocksource_select();
+        mutex_unlock(&clocksource_mutex);
+        return 0;
 }
+fs_initcall(clocksource_done_booting);
 
 /*
  * Enqueue the clocksource sorted by rating
  */
-static int clocksource_enqueue(struct clocksource *c)
+static void clocksource_enqueue(struct clocksource *cs)
 {
-        struct list_head *tmp, *entry = &clocksource_list;
+        struct list_head *entry = &clocksource_list;
+        struct clocksource *tmp;
 
-        list_for_each(tmp, &clocksource_list) {
-                struct clocksource *cs;
-
-                cs = list_entry(tmp, struct clocksource, list);
-                if (cs == c)
-                        return -EBUSY;
+        list_for_each_entry(tmp, &clocksource_list, list)
                 /* Keep track of the place, where to insert */
-                if (cs->rating >= c->rating)
-                        entry = tmp;
-        }
-        list_add(&c->list, entry);
-
-        if (strlen(c->name) == strlen(override_name) &&
-            !strcmp(c->name, override_name))
-                clocksource_override = c;
-
-        return 0;
+                if (tmp->rating >= cs->rating)
+                        entry = &tmp->list;
+        list_add(&cs->list, entry);
 }
 
 /**
@@ -397,52 +509,48 @@ static int clocksource_enqueue(struct clocksource *c)
  *
  * Returns -EBUSY if registration fails, zero otherwise.
  */
-int clocksource_register(struct clocksource *c)
+int clocksource_register(struct clocksource *cs)
 {
-        unsigned long flags;
-        int ret;
-
-        spin_lock_irqsave(&clocksource_lock, flags);
-        ret = clocksource_enqueue(c);
-        if (!ret)
-                next_clocksource = select_clocksource();
-        spin_unlock_irqrestore(&clocksource_lock, flags);
-        if (!ret)
-                clocksource_check_watchdog(c);
-        return ret;
+        mutex_lock(&clocksource_mutex);
+        clocksource_enqueue(cs);
+        clocksource_select();
+        clocksource_enqueue_watchdog(cs);
+        mutex_unlock(&clocksource_mutex);
+        return 0;
 }
 EXPORT_SYMBOL(clocksource_register);
 
+static void __clocksource_change_rating(struct clocksource *cs, int rating)
+{
+        list_del(&cs->list);
+        cs->rating = rating;
+        clocksource_enqueue(cs);
+        clocksource_select();
+}
+
 /**
  * clocksource_change_rating - Change the rating of a registered clocksource
- *
  */
 void clocksource_change_rating(struct clocksource *cs, int rating)
 {
-        unsigned long flags;
-
-        spin_lock_irqsave(&clocksource_lock, flags);
-        list_del(&cs->list);
-        cs->rating = rating;
-        clocksource_enqueue(cs);
-        next_clocksource = select_clocksource();
-        spin_unlock_irqrestore(&clocksource_lock, flags);
+        mutex_lock(&clocksource_mutex);
+        __clocksource_change_rating(cs, rating);
+        mutex_unlock(&clocksource_mutex);
 }
+EXPORT_SYMBOL(clocksource_change_rating);
 
 /**
  * clocksource_unregister - remove a registered clocksource
  */
 void clocksource_unregister(struct clocksource *cs)
 {
-        unsigned long flags;
-
-        spin_lock_irqsave(&clocksource_lock, flags);
+        mutex_lock(&clocksource_mutex);
+        clocksource_dequeue_watchdog(cs);
         list_del(&cs->list);
-        if (clocksource_override == cs)
-                clocksource_override = NULL;
-        next_clocksource = select_clocksource();
-        spin_unlock_irqrestore(&clocksource_lock, flags);
+        clocksource_select();
+        mutex_unlock(&clocksource_mutex);
 }
+EXPORT_SYMBOL(clocksource_unregister);
 
 #ifdef CONFIG_SYSFS
 /**
@@ -458,9 +566,9 @@ sysfs_show_current_clocksources(struct sys_device *dev,
 {
         ssize_t count = 0;
 
-        spin_lock_irq(&clocksource_lock);
+        mutex_lock(&clocksource_mutex);
         count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
-        spin_unlock_irq(&clocksource_lock);
+        mutex_unlock(&clocksource_mutex);
 
         return count;
 }
@@ -478,9 +586,7 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
                                           struct sysdev_attribute *attr,
                                           const char *buf, size_t count)
 {
-        struct clocksource *ovr = NULL;
         size_t ret = count;
-        int len;
 
         /* strings from sysfs write are not 0 terminated! */
         if (count >= sizeof(override_name))
@@ -490,44 +596,14 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
         if (buf[count-1] == '\n')
                 count--;
 
-        spin_lock_irq(&clocksource_lock);
+        mutex_lock(&clocksource_mutex);
 
         if (count > 0)
                 memcpy(override_name, buf, count);
         override_name[count] = 0;
+        clocksource_select();
 
-        len = strlen(override_name);
-        if (len) {
-                struct clocksource *cs;
-
-                ovr = clocksource_override;
-                /* try to select it: */
-                list_for_each_entry(cs, &clocksource_list, list) {
-                        if (strlen(cs->name) == len &&
-                            !strcmp(cs->name, override_name))
-                                ovr = cs;
-                }
-        }
-
-        /*
-         * Check to make sure we don't switch to a non-highres capable
-         * clocksource if the tick code is in oneshot mode (highres or nohz)
-         */
-        if (tick_oneshot_mode_active() && ovr &&
-            !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) {
-                printk(KERN_WARNING "%s clocksource is not HRT compatible. "
-                        "Cannot switch while in HRT/NOHZ mode\n", ovr->name);
-                ovr = NULL;
-                override_name[0] = 0;
-        }
-
-        /* Reselect, when the override name has changed */
-        if (ovr != clocksource_override) {
-                clocksource_override = ovr;
-                next_clocksource = select_clocksource();
-        }
-
-        spin_unlock_irq(&clocksource_lock);
+        mutex_unlock(&clocksource_mutex);
 
         return ret;
 }
@@ -547,7 +623,7 @@ sysfs_show_available_clocksources(struct sys_device *dev,
         struct clocksource *src;
         ssize_t count = 0;
 
-        spin_lock_irq(&clocksource_lock);
+        mutex_lock(&clocksource_mutex);
         list_for_each_entry(src, &clocksource_list, list) {
                 /*
                  * Don't show non-HRES clocksource if the tick code is
@@ -559,7 +635,7 @@ sysfs_show_available_clocksources(struct sys_device *dev,
                                   max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
                                   "%s ", src->name);
         }
-        spin_unlock_irq(&clocksource_lock);
+        mutex_unlock(&clocksource_mutex);
 
         count += snprintf(buf + count,
                           max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
@@ -614,11 +690,10 @@ device_initcall(init_clocksource_sysfs);
  */
 static int __init boot_override_clocksource(char* str)
 {
-        unsigned long flags;
-        spin_lock_irqsave(&clocksource_lock, flags);
+        mutex_lock(&clocksource_mutex);
         if (str)
                 strlcpy(override_name, str, sizeof(override_name));
-        spin_unlock_irqrestore(&clocksource_lock, flags);
+        mutex_unlock(&clocksource_mutex);
         return 1;
 }
 
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index c3f6c30816e3..5404a8456909 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -61,7 +61,6 @@ struct clocksource clocksource_jiffies = {
         .read           = jiffies_read,
         .mask           = 0xffffffff, /*32bits*/
         .mult           = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
-        .mult_orig      = NSEC_PER_JIFFY << JIFFIES_SHIFT,
         .shift          = JIFFIES_SHIFT,
 };
 
@@ -71,3 +70,8 @@ static int __init init_jiffies_clocksource(void)
 }
 
 core_initcall(init_jiffies_clocksource);
+
+struct clocksource * __init __weak clocksource_default_clock(void)
+{
+        return &clocksource_jiffies;
+}
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 7fc64375ff43..4800f933910e 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -194,8 +194,7 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
         case TIME_OK:
                 break;
         case TIME_INS:
-                xtime.tv_sec--;
-                wall_to_monotonic.tv_sec++;
+                timekeeping_leap_insert(-1);
                 time_state = TIME_OOP;
                 printk(KERN_NOTICE
                         "Clock: inserting leap second 23:59:60 UTC\n");
@@ -203,9 +202,8 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
                 res = HRTIMER_RESTART;
                 break;
         case TIME_DEL:
-                xtime.tv_sec++;
+                timekeeping_leap_insert(1);
                 time_tai--;
-                wall_to_monotonic.tv_sec--;
                 time_state = TIME_WAIT;
                 printk(KERN_NOTICE
                         "Clock: deleting leap second 23:59:59 UTC\n");
@@ -219,7 +217,6 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
                         time_state = TIME_OK;
                 break;
         }
-        update_vsyscall(&xtime, clock);
 
         write_sequnlock(&xtime_lock);
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index e0f59a21c061..89aed5933ed4 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -231,6 +231,13 @@ void tick_nohz_stop_sched_tick(int inidle)
         if (!inidle && !ts->inidle)
                 goto end;
 
+        /*
+         * Set ts->inidle unconditionally. Even if the system did not
+         * switch to NOHZ mode the cpu frequency governers rely on the
+         * update of the idle time accounting in tick_nohz_start_idle().
+         */
+        ts->inidle = 1;
+
         now = tick_nohz_start_idle(ts);
 
         /*
@@ -248,8 +255,6 @@ void tick_nohz_stop_sched_tick(int inidle)
         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
                 goto end;
 
-        ts->inidle = 1;
-
         if (need_resched())
                 goto end;
 
diff --git a/kernel/time/timeconv.c b/kernel/time/timeconv.c
new file mode 100644
index 000000000000..86628e755f38
--- /dev/null
+++ b/kernel/time/timeconv.c
@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
+ * This file is part of the GNU C Library.
+ * Contributed by Paul Eggert (eggert@twinsun.com).
+ *
+ * The GNU C Library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * The GNU C Library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with the GNU C Library; see the file COPYING.LIB.  If not,
+ * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+/*
+ * Converts the calendar time to broken-down time representation
+ * Based on code from glibc-2.6
+ *
+ * 2009-7-14:
+ *   Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
+ */
+
+#include <linux/time.h>
+#include <linux/module.h>
+
+/*
+ * Nonzero if YEAR is a leap year (every 4 years,
+ * except every 100th isn't, and every 400th is).
+ */
+static int __isleap(long year)
+{
+        return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
+}
+
+/* do a mathdiv for long type */
+static long math_div(long a, long b)
+{
+        return a / b - (a % b < 0);
+}
+
+/* How many leap years between y1 and y2, y1 must less or equal to y2 */
+static long leaps_between(long y1, long y2)
+{
+        long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
+                + math_div(y1 - 1, 400);
+        long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
+                + math_div(y2 - 1, 400);
+        return leaps2 - leaps1;
+}
+
+/* How many days come before each month (0-12). */
+static const unsigned short __mon_yday[2][13] = {
+        /* Normal years. */
+        {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
+        /* Leap years. */
+        {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
+};
+
+#define SECS_PER_HOUR   (60 * 60)
+#define SECS_PER_DAY    (SECS_PER_HOUR * 24)
+
+/**
+ * time_to_tm - converts the calendar time to local broken-down time
+ *
+ * @totalsecs   the number of seconds elapsed since 00:00:00 on January 1, 1970,
+ *              Coordinated Universal Time (UTC).
+ * @offset      offset seconds adding to totalsecs.
+ * @result      pointer to struct tm variable to receive broken-down time
+ */
+void time_to_tm(time_t totalsecs, int offset, struct tm *result)
+{
+        long days, rem, y;
+        const unsigned short *ip;
+
+        days = totalsecs / SECS_PER_DAY;
+        rem = totalsecs % SECS_PER_DAY;
+        rem += offset;
+        while (rem < 0) {
+                rem += SECS_PER_DAY;
+                --days;
+        }
+        while (rem >= SECS_PER_DAY) {
+                rem -= SECS_PER_DAY;
+                ++days;
+        }
+
+        result->tm_hour = rem / SECS_PER_HOUR;
+        rem %= SECS_PER_HOUR;
+        result->tm_min = rem / 60;
+        result->tm_sec = rem % 60;
+
+        /* January 1, 1970 was a Thursday. */
+        result->tm_wday = (4 + days) % 7;
+        if (result->tm_wday < 0)
+                result->tm_wday += 7;
+
+        y = 1970;
+
+        while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
+                /* Guess a corrected year, assuming 365 days per year. */
+                long yg = y + math_div(days, 365);
+
+                /* Adjust DAYS and Y to match the guessed year. */
+                days -= (yg - y) * 365 + leaps_between(y, yg);
+                y = yg;
+        }
+
+        result->tm_year = y - 1900;
+
+        result->tm_yday = days;
+
+        ip = __mon_yday[__isleap(y)];
+        for (y = 11; days < ip[y]; y--)
+                continue;
+        days -= ip[y];
+
+        result->tm_mon = y;
+        result->tm_mday = days + 1;
+}
+EXPORT_SYMBOL(time_to_tm);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e8c77d9c633a..c3a4e2907eaa 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -13,12 +13,123 @@
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <linux/mm.h>
+#include <linux/sched.h>
 #include <linux/sysdev.h>
 #include <linux/clocksource.h>
 #include <linux/jiffies.h>
 #include <linux/time.h>
 #include <linux/tick.h>
+#include <linux/stop_machine.h>
+
+/* Structure holding internal timekeeping values. */
+struct timekeeper {
+        /* Current clocksource used for timekeeping. */
+        struct clocksource *clock;
+        /* The shift value of the current clocksource. */
+        int     shift;
+
+        /* Number of clock cycles in one NTP interval. */
+        cycle_t cycle_interval;
+        /* Number of clock shifted nano seconds in one NTP interval. */
+        u64     xtime_interval;
+        /* Raw nano seconds accumulated per NTP interval. */
+        u32     raw_interval;
+
+        /* Clock shifted nano seconds remainder not stored in xtime.tv_nsec. */
+        u64     xtime_nsec;
+        /* Difference between accumulated time and NTP time in ntp
+         * shifted nano seconds. */
+        s64     ntp_error;
+        /* Shift conversion between clock shifted nano seconds and
+         * ntp shifted nano seconds. */
+        int     ntp_error_shift;
+        /* NTP adjusted clock multiplier */
+        u32     mult;
+};
+
+struct timekeeper timekeeper;
+
+/**
+ * timekeeper_setup_internals - Set up internals to use clocksource clock.
+ *
+ * @clock:              Pointer to clocksource.
+ *
+ * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
+ * pair and interval request.
+ *
+ * Unless you're the timekeeping code, you should not be using this!
+ */
+static void timekeeper_setup_internals(struct clocksource *clock)
+{
+        cycle_t interval;
+        u64 tmp;
+
+        timekeeper.clock = clock;
+        clock->cycle_last = clock->read(clock);
 
+        /* Do the ns -> cycle conversion first, using original mult */
+        tmp = NTP_INTERVAL_LENGTH;
+        tmp <<= clock->shift;
+        tmp += clock->mult/2;
+        do_div(tmp, clock->mult);
+        if (tmp == 0)
+                tmp = 1;
+
+        interval = (cycle_t) tmp;
+        timekeeper.cycle_interval = interval;
+
+        /* Go back from cycles -> shifted ns */
+        timekeeper.xtime_interval = (u64) interval * clock->mult;
+        timekeeper.raw_interval =
+                ((u64) interval * clock->mult) >> clock->shift;
+
+        timekeeper.xtime_nsec = 0;
+        timekeeper.shift = clock->shift;
+
+        timekeeper.ntp_error = 0;
+        timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
+
+        /*
+         * The timekeeper keeps its own mult values for the currently
+         * active clocksource. These value will be adjusted via NTP
+         * to counteract clock drifting.
+         */
+        timekeeper.mult = clock->mult;
+}
+
+/* Timekeeper helper functions. */
+static inline s64 timekeeping_get_ns(void)
+{
+        cycle_t cycle_now, cycle_delta;
+        struct clocksource *clock;
+
+        /* read clocksource: */
+        clock = timekeeper.clock;
+        cycle_now = clock->read(clock);
+
+        /* calculate the delta since the last update_wall_time: */
+        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+        /* return delta convert to nanoseconds using ntp adjusted mult. */
+        return clocksource_cyc2ns(cycle_delta, timekeeper.mult,
+                                  timekeeper.shift);
+}
+
+static inline s64 timekeeping_get_ns_raw(void)
+{
+        cycle_t cycle_now, cycle_delta;
+        struct clocksource *clock;
+
+        /* read clocksource: */
+        clock = timekeeper.clock;
+        cycle_now = clock->read(clock);
+
+        /* calculate the delta since the last update_wall_time: */
+        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+        /* return delta convert to nanoseconds using ntp adjusted mult. */
+        return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
+}
 
 /*
  * This read-write spinlock protects us from races in SMP while
@@ -44,7 +155,12 @@ __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
  */
 struct timespec xtime __attribute__ ((aligned (16)));
 struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
-static unsigned long total_sleep_time;          /* seconds */
+static struct timespec total_sleep_time;
+
+/*
+ * The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock.
+ */
+struct timespec raw_time;
 
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
@@ -56,35 +172,44 @@ void update_xtime_cache(u64 nsec)
         timespec_add_ns(&xtime_cache, nsec);
 }
 
-struct clocksource *clock;
-
+/* must hold xtime_lock */
+void timekeeping_leap_insert(int leapsecond)
+{
+        xtime.tv_sec += leapsecond;
+        wall_to_monotonic.tv_sec -= leapsecond;
+        update_vsyscall(&xtime, timekeeper.clock);
+}
 
 #ifdef CONFIG_GENERIC_TIME
+
 /**
- * clocksource_forward_now - update clock to the current time
+ * timekeeping_forward_now - update clock to the current time
  *
  * Forward the current clock to update its state since the last call to
  * update_wall_time(). This is useful before significant clock changes,
  * as it avoids having to deal with this time offset explicitly.
  */
-static void clocksource_forward_now(void)
+static void timekeeping_forward_now(void)
 {
         cycle_t cycle_now, cycle_delta;
+        struct clocksource *clock;
         s64 nsec;
 
-        cycle_now = clocksource_read(clock);
+        clock = timekeeper.clock;
+        cycle_now = clock->read(clock);
         cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
         clock->cycle_last = cycle_now;
 
-        nsec = cyc2ns(clock, cycle_delta);
+        nsec = clocksource_cyc2ns(cycle_delta, timekeeper.mult,
+                                  timekeeper.shift);
 
         /* If arch requires, add in gettimeoffset() */
         nsec += arch_gettimeoffset();
 
         timespec_add_ns(&xtime, nsec);
 
-        nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
-        clock->raw_time.tv_nsec += nsec;
+        nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
+        timespec_add_ns(&raw_time, nsec);
 }
 
 /**
@@ -95,7 +220,6 @@ static void clocksource_forward_now(void)
  */
 void getnstimeofday(struct timespec *ts)
 {
-        cycle_t cycle_now, cycle_delta;
         unsigned long seq;
         s64 nsecs;
 
@@ -105,15 +229,7 @@ void getnstimeofday(struct timespec *ts)
                 seq = read_seqbegin(&xtime_lock);
 
                 *ts = xtime;
-
-                /* read clocksource: */
-                cycle_now = clocksource_read(clock);
-
-                /* calculate the delta since the last update_wall_time: */
-                cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
-
-                /* convert to nanoseconds: */
-                nsecs = cyc2ns(clock, cycle_delta);
+                nsecs = timekeeping_get_ns();
 
                 /* If arch requires, add in gettimeoffset() */
                 nsecs += arch_gettimeoffset();
@@ -125,6 +241,57 @@ void getnstimeofday(struct timespec *ts)
 
 EXPORT_SYMBOL(getnstimeofday);
 
+ktime_t ktime_get(void)
+{
+        unsigned int seq;
+        s64 secs, nsecs;
+
+        WARN_ON(timekeeping_suspended);
+
+        do {
+                seq = read_seqbegin(&xtime_lock);
+                secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
+                nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
+                nsecs += timekeeping_get_ns();
+
+        } while (read_seqretry(&xtime_lock, seq));
+        /*
+         * Use ktime_set/ktime_add_ns to create a proper ktime on
+         * 32-bit architectures without CONFIG_KTIME_SCALAR.
+         */
+        return ktime_add_ns(ktime_set(secs, 0), nsecs);
+}
+EXPORT_SYMBOL_GPL(ktime_get);
+
+/**
+ * ktime_get_ts - get the monotonic clock in timespec format
+ * @ts:         pointer to timespec variable
+ *
+ * The function calculates the monotonic clock from the realtime
+ * clock and the wall_to_monotonic offset and stores the result
+ * in normalized timespec format in the variable pointed to by @ts.
+ */
+void ktime_get_ts(struct timespec *ts)
+{
+        struct timespec tomono;
+        unsigned int seq;
+        s64 nsecs;
+
+        WARN_ON(timekeeping_suspended);
+
+        do {
+                seq = read_seqbegin(&xtime_lock);
+                *ts = xtime;
+                tomono = wall_to_monotonic;
+                nsecs = timekeeping_get_ns();
+
+        } while (read_seqretry(&xtime_lock, seq));
+
+        set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
+                                ts->tv_nsec + tomono.tv_nsec + nsecs);
+}
+EXPORT_SYMBOL_GPL(ktime_get_ts);
+
 /**
  * do_gettimeofday - Returns the time of day in a timeval
  * @tv:         pointer to the timeval to be set
@@ -157,7 +324,7 @@ int do_settimeofday(struct timespec *tv)
 
         write_seqlock_irqsave(&xtime_lock, flags);
 
-        clocksource_forward_now();
+        timekeeping_forward_now();
 
         ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
         ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
@@ -167,10 +334,10 @@ int do_settimeofday(struct timespec *tv)
 
         update_xtime_cache(0);
 
-        clock->error = 0;
+        timekeeper.ntp_error = 0;
         ntp_clear();
 
-        update_vsyscall(&xtime, clock);
+        update_vsyscall(&xtime, timekeeper.clock);
 
         write_sequnlock_irqrestore(&xtime_lock, flags);
 
@@ -187,44 +354,97 @@ EXPORT_SYMBOL(do_settimeofday);
  *
  * Accumulates current time interval and initializes new clocksource
  */
-static void change_clocksource(void)
+static int change_clocksource(void *data)
 {
         struct clocksource *new, *old;
 
-        new = clocksource_get_next();
+        new = (struct clocksource *) data;
+
+        timekeeping_forward_now();
+        if (!new->enable || new->enable(new) == 0) {
+                old = timekeeper.clock;
+                timekeeper_setup_internals(new);
+                if (old->disable)
+                        old->disable(old);
+        }
+        return 0;
+}
 
-        if (clock == new)
+/**
+ * timekeeping_notify - Install a new clock source
+ * @clock:              pointer to the clock source
+ *
+ * This function is called from clocksource.c after a new, better clock
+ * source has been registered. The caller holds the clocksource_mutex.
+ */
+void timekeeping_notify(struct clocksource *clock)
+{
+        if (timekeeper.clock == clock)
                 return;
+        stop_machine(change_clocksource, clock, NULL);
+        tick_clock_notify();
+}
 
-        clocksource_forward_now();
+#else /* GENERIC_TIME */
 
-        if (clocksource_enable(new))
-                return;
+static inline void timekeeping_forward_now(void) { }
 
-        new->raw_time = clock->raw_time;
-        old = clock;
-        clock = new;
-        clocksource_disable(old);
+/**
+ * ktime_get - get the monotonic time in ktime_t format
+ *
+ * returns the time in ktime_t format
+ */
+ktime_t ktime_get(void)
+{
+        struct timespec now;
 
-        clock->cycle_last = 0;
-        clock->cycle_last = clocksource_read(clock);
-        clock->error = 0;
-        clock->xtime_nsec = 0;
-        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
+        ktime_get_ts(&now);
 
-        tick_clock_notify();
+        return timespec_to_ktime(now);
+}
+EXPORT_SYMBOL_GPL(ktime_get);
 
-        /*
-         * We're holding xtime lock and waking up klogd would deadlock
-         * us on enqueue.  So no printing!
-        printk(KERN_INFO "Time: %s clocksource has been installed.\n",
-               clock->name);
-         */
+/**
+ * ktime_get_ts - get the monotonic clock in timespec format
+ * @ts:         pointer to timespec variable
+ *
+ * The function calculates the monotonic clock from the realtime
+ * clock and the wall_to_monotonic offset and stores the result
+ * in normalized timespec format in the variable pointed to by @ts.
+ */
+void ktime_get_ts(struct timespec *ts)
+{
+        struct timespec tomono;
+        unsigned long seq;
+
+        do {
+                seq = read_seqbegin(&xtime_lock);
+                getnstimeofday(ts);
+                tomono = wall_to_monotonic;
+
+        } while (read_seqretry(&xtime_lock, seq));
+
+        set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
+                                ts->tv_nsec + tomono.tv_nsec);
 }
-#else
-static inline void clocksource_forward_now(void) { }
-static inline void change_clocksource(void) { }
-#endif
+EXPORT_SYMBOL_GPL(ktime_get_ts);
+
+#endif /* !GENERIC_TIME */
+
+/**
+ * ktime_get_real - get the real (wall-) time in ktime_t format
+ *
+ * returns the time in ktime_t format
+ */
+ktime_t ktime_get_real(void)
+{
+        struct timespec now;
+
+        getnstimeofday(&now);
+
+        return timespec_to_ktime(now);
+}
+EXPORT_SYMBOL_GPL(ktime_get_real);
 
 /**
  * getrawmonotonic - Returns the raw monotonic time in a timespec
@@ -236,21 +456,11 @@ void getrawmonotonic(struct timespec *ts)
 {
         unsigned long seq;
         s64 nsecs;
-        cycle_t cycle_now, cycle_delta;
 
         do {
                 seq = read_seqbegin(&xtime_lock);
-
-                /* read clocksource: */
-                cycle_now = clocksource_read(clock);
-
-                /* calculate the delta since the last update_wall_time: */
-                cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
-
-                /* convert to nanoseconds: */
-                nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
-
-                *ts = clock->raw_time;
+                nsecs = timekeeping_get_ns_raw();
+                *ts = raw_time;
 
         } while (read_seqretry(&xtime_lock, seq));
 
@@ -270,7 +480,7 @@ int timekeeping_valid_for_hres(void)
         do {
                 seq = read_seqbegin(&xtime_lock);
 
-                ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
+                ret = timekeeper.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
 
         } while (read_seqretry(&xtime_lock, seq));
 
@@ -278,17 +488,33 @@ int timekeeping_valid_for_hres(void)
 }
 
 /**
- * read_persistent_clock -  Return time in seconds from the persistent clock.
+ * read_persistent_clock -  Return time from the persistent clock.
  *
  * Weak dummy function for arches that do not yet support it.
- * Returns seconds from epoch using the battery backed persistent clock.
- * Returns zero if unsupported.
+ * Reads the time from the battery backed persistent clock.
+ * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
  *
  *  XXX - Do be sure to remove it once all arches implement it.
  */
-unsigned long __attribute__((weak)) read_persistent_clock(void)
+void __attribute__((weak)) read_persistent_clock(struct timespec *ts)
 {
-        return 0;
+        ts->tv_sec = 0;
+        ts->tv_nsec = 0;
+}
+
+/**
+ * read_boot_clock -  Return time of the system start.
+ *
+ * Weak dummy function for arches that do not yet support it.
+ * Function to read the exact time the system has been started.
+ * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
+ *
+ *  XXX - Do be sure to remove it once all arches implement it.
+ */
+void __attribute__((weak)) read_boot_clock(struct timespec *ts)
+{
+        ts->tv_sec = 0;
+        ts->tv_nsec = 0;
 }
 
 /*
@@ -296,29 +522,40 @@ unsigned long __attribute__((weak)) read_persistent_clock(void)
  */
 void __init timekeeping_init(void)
 {
+        struct clocksource *clock;
         unsigned long flags;
-        unsigned long sec = read_persistent_clock();
+        struct timespec now, boot;
+
+        read_persistent_clock(&now);
+        read_boot_clock(&boot);
 
         write_seqlock_irqsave(&xtime_lock, flags);
 
         ntp_init();
 
-        clock = clocksource_get_next();
-        clocksource_enable(clock);
-        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
-        clock->cycle_last = clocksource_read(clock);
-
-        xtime.tv_sec = sec;
-        xtime.tv_nsec = 0;
+        clock = clocksource_default_clock();
+        if (clock->enable)
+                clock->enable(clock);
+        timekeeper_setup_internals(clock);
+
+        xtime.tv_sec = now.tv_sec;
+        xtime.tv_nsec = now.tv_nsec;
+        raw_time.tv_sec = 0;
+        raw_time.tv_nsec = 0;
+        if (boot.tv_sec == 0 && boot.tv_nsec == 0) {
+                boot.tv_sec = xtime.tv_sec;
+                boot.tv_nsec = xtime.tv_nsec;
+        }
         set_normalized_timespec(&wall_to_monotonic,
-                -xtime.tv_sec, -xtime.tv_nsec);
+                                -boot.tv_sec, -boot.tv_nsec);
         update_xtime_cache(0);
-        total_sleep_time = 0;
+        total_sleep_time.tv_sec = 0;
+        total_sleep_time.tv_nsec = 0;
         write_sequnlock_irqrestore(&xtime_lock, flags);
 }
 
 /* time in seconds when suspend began */
-static unsigned long timekeeping_suspend_time;
+static struct timespec timekeeping_suspend_time;
 
 /**
  * timekeeping_resume - Resumes the generic timekeeping subsystem.
@@ -331,24 +568,24 @@ static unsigned long timekeeping_suspend_time;
 static int timekeeping_resume(struct sys_device *dev)
 {
         unsigned long flags;
-        unsigned long now = read_persistent_clock();
+        struct timespec ts;
+
+        read_persistent_clock(&ts);
 
         clocksource_resume();
 
         write_seqlock_irqsave(&xtime_lock, flags);
 
-        if (now && (now > timekeeping_suspend_time)) {
-                unsigned long sleep_length = now - timekeeping_suspend_time;
-
-                xtime.tv_sec += sleep_length;
-                wall_to_monotonic.tv_sec -= sleep_length;
-                total_sleep_time += sleep_length;
+        if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
+                ts = timespec_sub(ts, timekeeping_suspend_time);
+                xtime = timespec_add_safe(xtime, ts);
+                wall_to_monotonic = timespec_sub(wall_to_monotonic, ts);
+                total_sleep_time = timespec_add_safe(total_sleep_time, ts);
         }
         update_xtime_cache(0);
         /* re-base the last cycle value */
-        clock->cycle_last = 0;
-        clock->cycle_last = clocksource_read(clock);
-        clock->error = 0;
+        timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
+        timekeeper.ntp_error = 0;
         timekeeping_suspended = 0;
         write_sequnlock_irqrestore(&xtime_lock, flags);
 
@@ -366,10 +603,10 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
 {
         unsigned long flags;
 
-        timekeeping_suspend_time = read_persistent_clock();
+        read_persistent_clock(&timekeeping_suspend_time);
 
         write_seqlock_irqsave(&xtime_lock, flags);
-        clocksource_forward_now();
+        timekeeping_forward_now();
         timekeeping_suspended = 1;
         write_sequnlock_irqrestore(&xtime_lock, flags);
 
@@ -404,7 +641,7 @@ device_initcall(timekeeping_init_device);
  * If the error is already larger, we look ahead even further
  * to compensate for late or lost adjustments.
  */
-static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
+static __always_inline int timekeeping_bigadjust(s64 error, s64 *interval,
                                                  s64 *offset)
 {
         s64 tick_error, i;
@@ -420,7 +657,7 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
          * here.  This is tuned so that an error of about 1 msec is adjusted
          * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
          */
-        error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
+        error2 = timekeeper.ntp_error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
         error2 = abs(error2);
         for (look_ahead = 0; error2 > 0; look_ahead++)
                 error2 >>= 2;
@@ -429,8 +666,8 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
          * Now calculate the error in (1 << look_ahead) ticks, but first
          * remove the single look ahead already included in the error.
          */
-        tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
-        tick_error -= clock->xtime_interval >> 1;
+        tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
+        tick_error -= timekeeper.xtime_interval >> 1;
         error = ((error - tick_error) >> look_ahead) + tick_error;
 
         /* Finally calculate the adjustment shift value.  */
@@ -455,18 +692,18 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
  * this is optimized for the most common adjustments of -1,0,1,
  * for other values we can do a bit more work.
  */
-static void clocksource_adjust(s64 offset)
+static void timekeeping_adjust(s64 offset)
 {
-        s64 error, interval = clock->cycle_interval;
+        s64 error, interval = timekeeper.cycle_interval;
         int adj;
 
-        error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
+        error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
         if (error > interval) {
                 error >>= 2;
                 if (likely(error <= interval))
                         adj = 1;
                 else
-                        adj = clocksource_bigadjust(error, &interval, &offset);
+                        adj = timekeeping_bigadjust(error, &interval, &offset);
         } else if (error < -interval) {
                 error >>= 2;
                 if (likely(error >= -interval)) {
@@ -474,15 +711,15 @@ static void clocksource_adjust(s64 offset)
                         interval = -interval;
                         offset = -offset;
                 } else
-                        adj = clocksource_bigadjust(error, &interval, &offset);
+                        adj = timekeeping_bigadjust(error, &interval, &offset);
         } else
                 return;
 
-        clock->mult += adj;
-        clock->xtime_interval += interval;
-        clock->xtime_nsec -= offset;
-        clock->error -= (interval - offset) <<
-                        (NTP_SCALE_SHIFT - clock->shift);
+        timekeeper.mult += adj;
+        timekeeper.xtime_interval += interval;
+        timekeeper.xtime_nsec -= offset;
+        timekeeper.ntp_error -= (interval - offset) <<
+                                timekeeper.ntp_error_shift;
 }
 
 /**
@@ -492,53 +729,59 @@ static void clocksource_adjust(s64 offset)
  */
 void update_wall_time(void)
 {
+        struct clocksource *clock;
         cycle_t offset;
+        u64 nsecs;
 
         /* Make sure we're fully resumed: */
         if (unlikely(timekeeping_suspended))
                 return;
 
+        clock = timekeeper.clock;
 #ifdef CONFIG_GENERIC_TIME
-        offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
+        offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
 #else
-        offset = clock->cycle_interval;
+        offset = timekeeper.cycle_interval;
 #endif
-        clock->xtime_nsec = (s64)xtime.tv_nsec << clock->shift;
+        timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;
 
         /* normally this loop will run just once, however in the
          * case of lost or late ticks, it will accumulate correctly.
          */
-        while (offset >= clock->cycle_interval) {
+        while (offset >= timekeeper.cycle_interval) {
+                u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;
+
                 /* accumulate one interval */
-                offset -= clock->cycle_interval;
-                clock->cycle_last += clock->cycle_interval;
+                offset -= timekeeper.cycle_interval;
+                clock->cycle_last += timekeeper.cycle_interval;
 
-                clock->xtime_nsec += clock->xtime_interval;
-                if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
-                        clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
+                timekeeper.xtime_nsec += timekeeper.xtime_interval;
+                if (timekeeper.xtime_nsec >= nsecps) {
+                        timekeeper.xtime_nsec -= nsecps;
                         xtime.tv_sec++;
                         second_overflow();
                 }
 
-                clock->raw_time.tv_nsec += clock->raw_interval;
-                if (clock->raw_time.tv_nsec >= NSEC_PER_SEC) {
-                        clock->raw_time.tv_nsec -= NSEC_PER_SEC;
-                        clock->raw_time.tv_sec++;
+                raw_time.tv_nsec += timekeeper.raw_interval;
+                if (raw_time.tv_nsec >= NSEC_PER_SEC) {
+                        raw_time.tv_nsec -= NSEC_PER_SEC;
+                        raw_time.tv_sec++;
                 }
 
                 /* accumulate error between NTP and clock interval */
-                clock->error += tick_length;
-                clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
+                timekeeper.ntp_error += tick_length;
+                timekeeper.ntp_error -= timekeeper.xtime_interval <<
+                                        timekeeper.ntp_error_shift;
         }
 
         /* correct the clock when NTP error is too big */
-        clocksource_adjust(offset);
+        timekeeping_adjust(offset);
 
         /*
          * Since in the loop above, we accumulate any amount of time
          * in xtime_nsec over a second into xtime.tv_sec, its possible for
          * xtime_nsec to be fairly small after the loop. Further, if we're
-         * slightly speeding the clocksource up in clocksource_adjust(),
+         * slightly speeding the clocksource up in timekeeping_adjust(),
          * its possible the required corrective factor to xtime_nsec could
          * cause it to underflow.
          *
@@ -550,24 +793,25 @@ void update_wall_time(void)
          * We'll correct this error next time through this function, when
          * xtime_nsec is not as small.
          */
-        if (unlikely((s64)clock->xtime_nsec < 0)) {
-                s64 neg = -(s64)clock->xtime_nsec;
-                clock->xtime_nsec = 0;
-                clock->error += neg << (NTP_SCALE_SHIFT - clock->shift);
+        if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
+                s64 neg = -(s64)timekeeper.xtime_nsec;
+                timekeeper.xtime_nsec = 0;
+                timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
         }
 
         /* store full nanoseconds into xtime after rounding it up and
          * add the remainder to the error difference.
          */
-        xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1;
-        clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
-        clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift);
+        xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
+        timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
+        timekeeper.ntp_error += timekeeper.xtime_nsec <<
+                                timekeeper.ntp_error_shift;
 
-        update_xtime_cache(cyc2ns(clock, offset));
+        nsecs = clocksource_cyc2ns(offset, timekeeper.mult, timekeeper.shift);
+        update_xtime_cache(nsecs);
 
         /* check to see if there is a new clocksource to use */
-        change_clocksource();
-        update_vsyscall(&xtime, clock);
+        update_vsyscall(&xtime, timekeeper.clock);
 }
 
 /**
@@ -583,9 +827,12 @@ void update_wall_time(void)
  */
 void getboottime(struct timespec *ts)
 {
-        set_normalized_timespec(ts,
-                - (wall_to_monotonic.tv_sec + total_sleep_time),
-                - wall_to_monotonic.tv_nsec);
+        struct timespec boottime = {
+                .tv_sec = wall_to_monotonic.tv_sec + total_sleep_time.tv_sec,
+                .tv_nsec = wall_to_monotonic.tv_nsec + total_sleep_time.tv_nsec
+        };
+
+        set_normalized_timespec(ts, -boottime.tv_sec, -boottime.tv_nsec);
 }
 
 /**
@@ -594,7 +841,7 @@ void getboottime(struct timespec *ts)
  */
 void monotonic_to_bootbased(struct timespec *ts)
 {
-        ts->tv_sec += total_sleep_time;
+        *ts = timespec_add_safe(*ts, total_sleep_time);
 }
 
 unsigned long get_seconds(void)
@@ -603,6 +850,10 @@ unsigned long get_seconds(void)
 }
 EXPORT_SYMBOL(get_seconds);
 
+struct timespec __current_kernel_time(void)
+{
+        return xtime_cache;
+}
 
 struct timespec current_kernel_time(void)
 {
@@ -618,3 +869,20 @@ struct timespec current_kernel_time(void)
         return now;
 }
 EXPORT_SYMBOL(current_kernel_time);
+
+struct timespec get_monotonic_coarse(void)
+{
+        struct timespec now, mono;
+        unsigned long seq;
+
+        do {
+                seq = read_seqbegin(&xtime_lock);
+
+                now = xtime_cache;
+                mono = wall_to_monotonic;
+        } while (read_seqretry(&xtime_lock, seq));
+
+        set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
+                                now.tv_nsec + mono.tv_nsec);
+        return now;
+}
diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index fddd69d16e03..1b5b7aa2fdfd 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -275,7 +275,7 @@ static int timer_list_open(struct inode *inode, struct file *filp)
         return single_open(filp, timer_list_show, NULL);
 }
 
-static struct file_operations timer_list_fops = {
+static const struct file_operations timer_list_fops = {
         .open           = timer_list_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c
index 4cde8b9c716f..ee5681f8d7ec 100644
--- a/kernel/time/timer_stats.c
+++ b/kernel/time/timer_stats.c
@@ -395,7 +395,7 @@ static int tstats_open(struct inode *inode, struct file *filp)
         return single_open(filp, tstats_show, NULL);
 }
 
-static struct file_operations tstats_fops = {
+static const struct file_operations tstats_fops = {
         .open           = tstats_open,
         .read           = seq_read,
         .write          = tstats_write,