Initial import

1 files changed, 1020 insertions, 0 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
new file mode 100644
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--- /dev/null
+++ b/kernel/time/clocksource.c
@@ -0,0 +1,1020 @@
+/*
+ * linux/kernel/time/clocksource.c
+ *
+ * This file contains the functions which manage clocksource drivers.
+ *
+ * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * TODO WishList:
+ *   o Allow clocksource drivers to be unregistered
+ */
+
+#include <linux/device.h>
+#include <linux/clocksource.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
+#include <linux/tick.h>
+#include <linux/kthread.h>
+
+#include "tick-internal.h"
+#include "timekeeping_internal.h"
+
+/**
+ * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
+ * @mult:	pointer to mult variable
+ * @shift:	pointer to shift variable
+ * @from:	frequency to convert from
+ * @to:		frequency to convert to
+ * @maxsec:	guaranteed runtime conversion range in seconds
+ *
+ * The function evaluates the shift/mult pair for the scaled math
+ * operations of clocksources and clockevents.
+ *
+ * @to and @from are frequency values in HZ. For clock sources @to is
+ * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
+ * event @to is the counter frequency and @from is NSEC_PER_SEC.
+ *
+ * The @maxsec conversion range argument controls the time frame in
+ * seconds which must be covered by the runtime conversion with the
+ * calculated mult and shift factors. This guarantees that no 64bit
+ * overflow happens when the input value of the conversion is
+ * multiplied with the calculated mult factor. Larger ranges may
+ * reduce the conversion accuracy by chosing smaller mult and shift
+ * factors.
+ */
+void
+clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
+{
+	u64 tmp;
+	u32 sft, sftacc= 32;
+
+	/*
+	 * Calculate the shift factor which is limiting the conversion
+	 * range:
+	 */
+	tmp = ((u64)maxsec * from) >> 32;
+	while (tmp) {
+		tmp >>=1;
+		sftacc--;
+	}
+
+	/*
+	 * Find the conversion shift/mult pair which has the best
+	 * accuracy and fits the maxsec conversion range:
+	 */
+	for (sft = 32; sft > 0; sft--) {
+		tmp = (u64) to << sft;
+		tmp += from / 2;
+		do_div(tmp, from);
+		if ((tmp >> sftacc) == 0)
+			break;
+	}
+	*mult = tmp;
+	*shift = sft;
+}
+
+/*[Clocksource internal variables]---------
+ * curr_clocksource:
+ *	currently selected clocksource.
+ * clocksource_list:
+ *	linked list with the registered clocksources
+ * clocksource_mutex:
+ *	protects manipulations to curr_clocksource and the clocksource_list
+ * override_name:
+ *	Name of the user-specified clocksource.
+ */
+static struct clocksource *curr_clocksource;
+static LIST_HEAD(clocksource_list);
+static DEFINE_MUTEX(clocksource_mutex);
+static char override_name[CS_NAME_LEN];
+static int finished_booting;
+
+#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
+static void clocksource_watchdog_work(struct work_struct *work);
+static void clocksource_select(void);
+
+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 int watchdog_running;
+static atomic_t watchdog_reset_pending;
+
+static int clocksource_watchdog_kthread(void *data);
+static void __clocksource_change_rating(struct clocksource *cs, int rating);
+
+/*
+ * Interval: 0.5sec Threshold: 0.0625s
+ */
+#define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
+
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+	/*
+	 * 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);
+}
+
+/**
+ * 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;
+	cycle_t csnow, wdnow, cslast, wdlast, delta;
+	int64_t wd_nsec, cs_nsec;
+	int next_cpu, reset_pending;
+
+	spin_lock(&watchdog_lock);
+	if (!watchdog_running)
+		goto out;
+
+	reset_pending = atomic_read(&watchdog_reset_pending);
+
+	list_for_each_entry(cs, &watchdog_list, wd_list) {
+
+		/* Clocksource already marked unstable? */
+		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+			if (finished_booting)
+				schedule_work(&watchdog_work);
+			continue;
+		}
+
+		local_irq_disable();
+		csnow = cs->read(cs);
+		wdnow = watchdog->read(watchdog);
+		local_irq_enable();
+
+		/* Clocksource initialized ? */
+		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
+		    atomic_read(&watchdog_reset_pending)) {
+			cs->flags |= CLOCK_SOURCE_WATCHDOG;
+			cs->wd_last = wdnow;
+			cs->cs_last = csnow;
+			continue;
+		}
+
+		delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
+		wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
+					     watchdog->shift);
+
+		delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
+		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
+		wdlast = cs->wd_last; /* save these in case we print them */
+		cslast = cs->cs_last;
+		cs->cs_last = csnow;
+		cs->wd_last = wdnow;
+
+		if (atomic_read(&watchdog_reset_pending))
+			continue;
+
+		/* Check the deviation from the watchdog clocksource. */
+		if ((abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD)) {
+			pr_warn("timekeeping watchdog: Marking clocksource '%s' as unstable, because the skew is too large:\n", cs->name);
+			pr_warn("	'%s' wd_now: %llx wd_last: %llx mask: %llx\n",
+				watchdog->name, wdnow, wdlast, watchdog->mask);
+			pr_warn("	'%s' cs_now: %llx cs_last: %llx mask: %llx\n",
+				cs->name, csnow, cslast, cs->mask);
+			__clocksource_unstable(cs);
+			continue;
+		}
+
+		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
+		    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
+		    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
+			/* Mark it valid for high-res. */
+			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+
+			/*
+			 * clocksource_done_booting() will sort it if
+			 * finished_booting is not set yet.
+			 */
+			if (!finished_booting)
+				continue;
+
+			/*
+			 * If this is not the current clocksource let
+			 * the watchdog thread reselect it. Due to the
+			 * change to high res this clocksource might
+			 * be preferred now. If it is the current
+			 * clocksource let the tick code know about
+			 * that change.
+			 */
+			if (cs != curr_clocksource) {
+				cs->flags |= CLOCK_SOURCE_RESELECT;
+				schedule_work(&watchdog_work);
+			} else {
+				tick_clock_notify();
+			}
+		}
+	}
+
+	/*
+	 * We only clear the watchdog_reset_pending, when we did a
+	 * full cycle through all clocksources.
+	 */
+	if (reset_pending)
+		atomic_dec(&watchdog_reset_pending);
+
+	/*
+	 * 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_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)
+{
+	atomic_inc(&watchdog_reset_pending);
+}
+
+static void clocksource_enqueue_watchdog(struct clocksource *cs)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&watchdog_lock, flags);
+	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+		/* cs is a clocksource to be watched. */
+		list_add(&cs->wd_list, &watchdog_list);
+		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) {
+			watchdog = cs;
+			/* Reset watchdog cycles */
+			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)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&watchdog_lock, flags);
+	if (cs != watchdog) {
+		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+			/* cs is a watched clocksource. */
+			list_del_init(&cs->wd_list);
+			/* Check if the watchdog timer needs to be stopped. */
+			clocksource_stop_watchdog();
+		}
+	}
+	spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
+static int __clocksource_watchdog_kthread(void)
+{
+	struct clocksource *cs, *tmp;
+	unsigned long flags;
+	LIST_HEAD(unstable);
+	int select = 0;
+
+	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);
+			select = 1;
+		}
+		if (cs->flags & CLOCK_SOURCE_RESELECT) {
+			cs->flags &= ~CLOCK_SOURCE_RESELECT;
+			select = 1;
+		}
+	}
+	/* 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);
+	}
+	return select;
+}
+
+static int clocksource_watchdog_kthread(void *data)
+{
+	mutex_lock(&clocksource_mutex);
+	if (__clocksource_watchdog_kthread())
+		clocksource_select();
+	mutex_unlock(&clocksource_mutex);
+	return 0;
+}
+
+static bool clocksource_is_watchdog(struct clocksource *cs)
+{
+	return cs == watchdog;
+}
+
+#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) { }
+static inline int __clocksource_watchdog_kthread(void) { return 0; }
+static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
+void clocksource_mark_unstable(struct clocksource *cs) { }
+
+#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
+
+/**
+ * clocksource_suspend - suspend the clocksource(s)
+ */
+void clocksource_suspend(void)
+{
+	struct clocksource *cs;
+
+	list_for_each_entry_reverse(cs, &clocksource_list, list)
+		if (cs->suspend)
+			cs->suspend(cs);
+}
+
+/**
+ * clocksource_resume - resume the clocksource(s)
+ */
+void clocksource_resume(void)
+{
+	struct clocksource *cs;
+
+	list_for_each_entry(cs, &clocksource_list, list)
+		if (cs->resume)
+			cs->resume(cs);
+
+	clocksource_resume_watchdog();
+}
+
+/**
+ * clocksource_touch_watchdog - Update watchdog
+ *
+ * Update the watchdog after exception contexts such as kgdb so as not
+ * to incorrectly trip the watchdog. This might fail when the kernel
+ * was stopped in code which holds watchdog_lock.
+ */
+void clocksource_touch_watchdog(void)
+{
+	clocksource_resume_watchdog();
+}
+
+/**
+ * clocksource_max_adjustment- Returns max adjustment amount
+ * @cs:         Pointer to clocksource
+ *
+ */
+static u32 clocksource_max_adjustment(struct clocksource *cs)
+{
+	u64 ret;
+	/*
+	 * We won't try to correct for more than 11% adjustments (110,000 ppm),
+	 */
+	ret = (u64)cs->mult * 11;
+	do_div(ret,100);
+	return (u32)ret;
+}
+
+/**
+ * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
+ * @mult:	cycle to nanosecond multiplier
+ * @shift:	cycle to nanosecond divisor (power of two)
+ * @maxadj:	maximum adjustment value to mult (~11%)
+ * @mask:	bitmask for two's complement subtraction of non 64 bit counters
+ * @max_cyc:	maximum cycle value before potential overflow (does not include
+ *		any safety margin)
+ *
+ * NOTE: This function includes a safety margin of 50%, in other words, we
+ * return half the number of nanoseconds the hardware counter can technically
+ * cover. This is done so that we can potentially detect problems caused by
+ * delayed timers or bad hardware, which might result in time intervals that
+ * are larger then what the math used can handle without overflows.
+ */
+u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
+{
+	u64 max_nsecs, max_cycles;
+
+	/*
+	 * Calculate the maximum number of cycles that we can pass to the
+	 * cyc2ns() function without overflowing a 64-bit result.
+	 */
+	max_cycles = ULLONG_MAX;
+	do_div(max_cycles, mult+maxadj);
+
+	/*
+	 * The actual maximum number of cycles we can defer the clocksource is
+	 * determined by the minimum of max_cycles and mask.
+	 * Note: Here we subtract the maxadj to make sure we don't sleep for
+	 * too long if there's a large negative adjustment.
+	 */
+	max_cycles = min(max_cycles, mask);
+	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
+
+	/* return the max_cycles value as well if requested */
+	if (max_cyc)
+		*max_cyc = max_cycles;
+
+	/* Return 50% of the actual maximum, so we can detect bad values */
+	max_nsecs >>= 1;
+
+	return max_nsecs;
+}
+
+/**
+ * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
+ * @cs:         Pointer to clocksource to be updated
+ *
+ */
+static inline void clocksource_update_max_deferment(struct clocksource *cs)
+{
+	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
+						cs->maxadj, cs->mask,
+						&cs->max_cycles);
+}
+
+#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
+
+static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
+{
+	struct clocksource *cs;
+
+	if (!finished_booting || list_empty(&clocksource_list))
+		return NULL;
+
+	/*
+	 * We pick the clocksource with the highest rating. If oneshot
+	 * mode is active, we pick the highres valid clocksource with
+	 * the best rating.
+	 */
+	list_for_each_entry(cs, &clocksource_list, list) {
+		if (skipcur && cs == curr_clocksource)
+			continue;
+		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
+			continue;
+		return cs;
+	}
+	return NULL;
+}
+
+static void __clocksource_select(bool skipcur)
+{
+	bool oneshot = tick_oneshot_mode_active();
+	struct clocksource *best, *cs;
+
+	/* Find the best suitable clocksource */
+	best = clocksource_find_best(oneshot, skipcur);
+	if (!best)
+		return;
+
+	/* Check for the override clocksource. */
+	list_for_each_entry(cs, &clocksource_list, list) {
+		if (skipcur && cs == curr_clocksource)
+			continue;
+		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) && oneshot) {
+			/* 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 && !timekeeping_notify(best)) {
+		pr_info("Switched to clocksource %s\n", best->name);
+		curr_clocksource = best;
+	}
+}
+
+/**
+ * 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.
+ */
+static void clocksource_select(void)
+{
+	return __clocksource_select(false);
+}
+
+static void clocksource_select_fallback(void)
+{
+	return __clocksource_select(true);
+}
+
+#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
+
+static inline void clocksource_select(void) { }
+static inline void clocksource_select_fallback(void) { }
+
+#endif
+
+/*
+ * 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)
+{
+	mutex_lock(&clocksource_mutex);
+	curr_clocksource = clocksource_default_clock();
+	finished_booting = 1;
+	/*
+	 * Run the watchdog first to eliminate unstable clock sources
+	 */
+	__clocksource_watchdog_kthread();
+	clocksource_select();
+	mutex_unlock(&clocksource_mutex);
+	return 0;
+}
+fs_initcall(clocksource_done_booting);
+
+/*
+ * Enqueue the clocksource sorted by rating
+ */
+static void clocksource_enqueue(struct clocksource *cs)
+{
+	struct list_head *entry = &clocksource_list;
+	struct clocksource *tmp;
+
+	list_for_each_entry(tmp, &clocksource_list, list)
+		/* Keep track of the place, where to insert */
+		if (tmp->rating >= cs->rating)
+			entry = &tmp->list;
+	list_add(&cs->list, entry);
+}
+
+/**
+ * __clocksource_update_freq_scale - Used update clocksource with new freq
+ * @cs:		clocksource to be registered
+ * @scale:	Scale factor multiplied against freq to get clocksource hz
+ * @freq:	clocksource frequency (cycles per second) divided by scale
+ *
+ * This should only be called from the clocksource->enable() method.
+ *
+ * This *SHOULD NOT* be called directly! Please use the
+ * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
+ * functions.
+ */
+void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
+{
+	u64 sec;
+
+	/*
+	 * Default clocksources are *special* and self-define their mult/shift.
+	 * But, you're not special, so you should specify a freq value.
+	 */
+	if (freq) {
+		/*
+		 * Calc the maximum number of seconds which we can run before
+		 * wrapping around. For clocksources which have a mask > 32-bit
+		 * we need to limit the max sleep time to have a good
+		 * conversion precision. 10 minutes is still a reasonable
+		 * amount. That results in a shift value of 24 for a
+		 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
+		 * ~ 0.06ppm granularity for NTP.
+		 */
+		sec = cs->mask;
+		do_div(sec, freq);
+		do_div(sec, scale);
+		if (!sec)
+			sec = 1;
+		else if (sec > 600 && cs->mask > UINT_MAX)
+			sec = 600;
+
+		clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
+				       NSEC_PER_SEC / scale, sec * scale);
+	}
+	/*
+	 * Ensure clocksources that have large 'mult' values don't overflow
+	 * when adjusted.
+	 */
+	cs->maxadj = clocksource_max_adjustment(cs);
+	while (freq && ((cs->mult + cs->maxadj < cs->mult)
+		|| (cs->mult - cs->maxadj > cs->mult))) {
+		cs->mult >>= 1;
+		cs->shift--;
+		cs->maxadj = clocksource_max_adjustment(cs);
+	}
+
+	/*
+	 * Only warn for *special* clocksources that self-define
+	 * their mult/shift values and don't specify a freq.
+	 */
+	WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
+		"timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
+		cs->name);
+
+	clocksource_update_max_deferment(cs);
+
+	pr_info("clocksource %s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
+			cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
+}
+EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
+
+/**
+ * __clocksource_register_scale - Used to install new clocksources
+ * @cs:		clocksource to be registered
+ * @scale:	Scale factor multiplied against freq to get clocksource hz
+ * @freq:	clocksource frequency (cycles per second) divided by scale
+ *
+ * Returns -EBUSY if registration fails, zero otherwise.
+ *
+ * This *SHOULD NOT* be called directly! Please use the
+ * clocksource_register_hz() or clocksource_register_khz helper functions.
+ */
+int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
+{
+
+	/* Initialize mult/shift and max_idle_ns */
+	__clocksource_update_freq_scale(cs, scale, freq);
+
+	/* Add clocksource to the clocksource list */
+	mutex_lock(&clocksource_mutex);
+	clocksource_enqueue(cs);
+	clocksource_enqueue_watchdog(cs);
+	clocksource_select();
+	mutex_unlock(&clocksource_mutex);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__clocksource_register_scale);
+
+static void __clocksource_change_rating(struct clocksource *cs, int rating)
+{
+	list_del(&cs->list);
+	cs->rating = rating;
+	clocksource_enqueue(cs);
+}
+
+/**
+ * clocksource_change_rating - Change the rating of a registered clocksource
+ * @cs:		clocksource to be changed
+ * @rating:	new rating
+ */
+void clocksource_change_rating(struct clocksource *cs, int rating)
+{
+	mutex_lock(&clocksource_mutex);
+	__clocksource_change_rating(cs, rating);
+	clocksource_select();
+	mutex_unlock(&clocksource_mutex);
+}
+EXPORT_SYMBOL(clocksource_change_rating);
+
+/*
+ * Unbind clocksource @cs. Called with clocksource_mutex held
+ */
+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 (cs == curr_clocksource) {
+		/* Select and try to install a replacement clock source */
+		clocksource_select_fallback();
+		if (curr_clocksource == cs)
+			return -EBUSY;
+	}
+	clocksource_dequeue_watchdog(cs);
+	list_del_init(&cs->list);
+	return 0;
+}
+
+/**
+ * clocksource_unregister - remove a registered clocksource
+ * @cs:	clocksource to be unregistered
+ */
+int clocksource_unregister(struct clocksource *cs)
+{
+	int ret = 0;
+
+	mutex_lock(&clocksource_mutex);
+	if (!list_empty(&cs->list))
+		ret = clocksource_unbind(cs);
+	mutex_unlock(&clocksource_mutex);
+	return ret;
+}
+EXPORT_SYMBOL(clocksource_unregister);
+
+#ifdef CONFIG_SYSFS
+/**
+ * sysfs_show_current_clocksources - sysfs interface for current clocksource
+ * @dev:	unused
+ * @attr:	unused
+ * @buf:	char buffer to be filled with clocksource list
+ *
+ * Provides sysfs interface for listing current clocksource.
+ */
+static ssize_t
+sysfs_show_current_clocksources(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	ssize_t count = 0;
+
+	mutex_lock(&clocksource_mutex);
+	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
+	mutex_unlock(&clocksource_mutex);
+
+	return count;
+}
+
+ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
+{
+	size_t ret = cnt;
+
+	/* strings from sysfs write are not 0 terminated! */
+	if (!cnt || cnt >= CS_NAME_LEN)
+		return -EINVAL;
+
+	/* strip of \n: */
+	if (buf[cnt-1] == '\n')
+		cnt--;
+	if (cnt > 0)
+		memcpy(dst, buf, cnt);
+	dst[cnt] = 0;
+	return ret;
+}
+
+/**
+ * sysfs_override_clocksource - interface for manually overriding clocksource
+ * @dev:	unused
+ * @attr:	unused
+ * @buf:	name of override clocksource
+ * @count:	length of buffer
+ *
+ * Takes input from sysfs interface for manually overriding the default
+ * clocksource selection.
+ */
+static ssize_t sysfs_override_clocksource(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t count)
+{
+	ssize_t ret;
+
+	mutex_lock(&clocksource_mutex);
+
+	ret = sysfs_get_uname(buf, override_name, count);
+	if (ret >= 0)
+		clocksource_select();
+
+	mutex_unlock(&clocksource_mutex);
+
+	return ret;
+}
+
+/**
+ * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
+ * @dev:	unused
+ * @attr:	unused
+ * @buf:	unused
+ * @count:	length of buffer
+ *
+ * Takes input from sysfs interface for manually unbinding a clocksource.
+ */
+static ssize_t sysfs_unbind_clocksource(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct clocksource *cs;
+	char name[CS_NAME_LEN];
+	ssize_t ret;
+
+	ret = sysfs_get_uname(buf, name, count);
+	if (ret < 0)
+		return ret;
+
+	ret = -ENODEV;
+	mutex_lock(&clocksource_mutex);
+	list_for_each_entry(cs, &clocksource_list, list) {
+		if (strcmp(cs->name, name))
+			continue;
+		ret = clocksource_unbind(cs);
+		break;
+	}
+	mutex_unlock(&clocksource_mutex);
+
+	return ret ? ret : count;
+}
+
+/**
+ * sysfs_show_available_clocksources - sysfs interface for listing clocksource
+ * @dev:	unused
+ * @attr:	unused
+ * @buf:	char buffer to be filled with clocksource list
+ *
+ * Provides sysfs interface for listing registered clocksources
+ */
+static ssize_t
+sysfs_show_available_clocksources(struct device *dev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	struct clocksource *src;
+	ssize_t count = 0;
+
+	mutex_lock(&clocksource_mutex);
+	list_for_each_entry(src, &clocksource_list, list) {
+		/*
+		 * Don't show non-HRES clocksource if the tick code is
+		 * in one shot mode (highres=on or nohz=on)
+		 */
+		if (!tick_oneshot_mode_active() ||
+		    (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
+			count += snprintf(buf + count,
+				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
+				  "%s ", src->name);
+	}
+	mutex_unlock(&clocksource_mutex);
+
+	count += snprintf(buf + count,
+			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
+
+	return count;
+}
+
+/*
+ * Sysfs setup bits:
+ */
+static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
+		   sysfs_override_clocksource);
+
+static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
+
+static DEVICE_ATTR(available_clocksource, 0444,
+		   sysfs_show_available_clocksources, NULL);
+
+static struct bus_type clocksource_subsys = {
+	.name = "clocksource",
+	.dev_name = "clocksource",
+};
+
+static struct device device_clocksource = {
+	.id	= 0,
+	.bus	= &clocksource_subsys,
+};
+
+static int __init init_clocksource_sysfs(void)
+{
+	int error = subsys_system_register(&clocksource_subsys, NULL);
+
+	if (!error)
+		error = device_register(&device_clocksource);
+	if (!error)
+		error = device_create_file(
+				&device_clocksource,
+				&dev_attr_current_clocksource);
+	if (!error)
+		error = device_create_file(&device_clocksource,
+					   &dev_attr_unbind_clocksource);
+	if (!error)
+		error = device_create_file(
+				&device_clocksource,
+				&dev_attr_available_clocksource);
+	return error;
+}
+
+device_initcall(init_clocksource_sysfs);
+#endif /* CONFIG_SYSFS */
+
+/**
+ * boot_override_clocksource - boot clock override
+ * @str:	override name
+ *
+ * Takes a clocksource= boot argument and uses it
+ * as the clocksource override name.
+ */
+static int __init boot_override_clocksource(char* str)
+{
+	mutex_lock(&clocksource_mutex);
+	if (str)
+		strlcpy(override_name, str, sizeof(override_name));
+	mutex_unlock(&clocksource_mutex);
+	return 1;
+}
+
+__setup("clocksource=", boot_override_clocksource);
+
+/**
+ * boot_override_clock - Compatibility layer for deprecated boot option
+ * @str:	override name
+ *
+ * DEPRECATED! Takes a clock= boot argument and uses it
+ * as the clocksource override name
+ */
+static int __init boot_override_clock(char* str)
+{
+	if (!strcmp(str, "pmtmr")) {
+		printk("Warning: clock=pmtmr is deprecated. "
+			"Use clocksource=acpi_pm.\n");
+		return boot_override_clocksource("acpi_pm");
+	}
+	printk("Warning! clock= boot option is deprecated. "
+		"Use clocksource=xyz\n");
+	return boot_override_clocksource(str);
+}
+
+__setup("clock=", boot_override_clock);