OSCL-LXR linux-6.0.1/​kernel/​time/​clocksource.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * This file contains the functions which manage clocksource drivers.
  *
  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #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 <linux/prandom.h>
 #include <linux/cpu.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 choosing 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;
 }
 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
 
 /*[Clocksource internal variables]---------
  * curr_clocksource:
  *  currently selected clocksource.
  * suspend_clocksource:
  *  used to calculate the suspend time.
  * 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 struct clocksource *suspend_clocksource;
 static LIST_HEAD(clocksource_list);
 static DEFINE_MUTEX(clocksource_mutex);
 static char override_name[CS_NAME_LEN];
 static int finished_booting;
 static u64 suspend_start;
 
 /*
  * Threshold: 0.0312s, when doubled: 0.0625s.
  * Also a default for cs->uncertainty_margin when registering clocks.
  */
 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
 
 /*
  * Maximum permissible delay between two readouts of the watchdog
  * clocksource surrounding a read of the clocksource being validated.
  * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
  * a lower bound for cs->uncertainty_margin values when registering clocks.
  */
 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
 #define MAX_SKEW_USEC   CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
 #else
 #define MAX_SKEW_USEC   100
 #endif
 
 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
 
 #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 inline void clocksource_watchdog_lock(unsigned long *flags)
 {
     spin_lock_irqsave(&watchdog_lock, *flags);
 }
 
 static inline void clocksource_watchdog_unlock(unsigned long *flags)
 {
     spin_unlock_irqrestore(&watchdog_lock, *flags);
 }
 
 static int clocksource_watchdog_kthread(void *data);
 static void __clocksource_change_rating(struct clocksource *cs, int rating);
 
 /*
  * Interval: 0.5sec.
  */
 #define WATCHDOG_INTERVAL (HZ >> 1)
 
 static void clocksource_watchdog_work(struct work_struct *work)
 {
     /*
      * We cannot directly run clocksource_watchdog_kthread() here, because
      * clocksource_select() calls timekeeping_notify() which uses
      * stop_machine(). One cannot use stop_machine() from a workqueue() due
      * lock inversions wrt CPU hotplug.
      *
      * Also, we only ever run this work once or twice during the lifetime
      * of the kernel, so there is no point in creating a more permanent
      * kthread for this.
      *
      * 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 the clocksource is registered clocksource_watchdog_kthread() will
      * re-rate and re-select.
      */
     if (list_empty(&cs->list)) {
         cs->rating = 0;
         return;
     }
 
     if (cs->mark_unstable)
         cs->mark_unstable(cs);
 
     /* kick clocksource_watchdog_kthread() */
     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 by the x86 TSC code to mark clocksources as unstable;
  * it defers demotion and re-selection to a kthread.
  */
 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->list) && list_empty(&cs->wd_list))
             list_add(&cs->wd_list, &watchdog_list);
         __clocksource_unstable(cs);
     }
     spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
 ulong max_cswd_read_retries = 2;
 module_param(max_cswd_read_retries, ulong, 0644);
 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
 static int verify_n_cpus = 8;
 module_param(verify_n_cpus, int, 0644);
 
 enum wd_read_status {
     WD_READ_SUCCESS,
     WD_READ_UNSTABLE,
     WD_READ_SKIP
 };
 
 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
 {
     unsigned int nretries;
     u64 wd_end, wd_end2, wd_delta;
     int64_t wd_delay, wd_seq_delay;
 
     for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
         local_irq_disable();
         *wdnow = watchdog->read(watchdog);
         *csnow = cs->read(cs);
         wd_end = watchdog->read(watchdog);
         wd_end2 = watchdog->read(watchdog);
         local_irq_enable();
 
         wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
         wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
                           watchdog->shift);
         if (wd_delay <= WATCHDOG_MAX_SKEW) {
             if (nretries > 1 || nretries >= max_cswd_read_retries) {
                 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
                     smp_processor_id(), watchdog->name, nretries);
             }
             return WD_READ_SUCCESS;
         }
 
         /*
          * Now compute delay in consecutive watchdog read to see if
          * there is too much external interferences that cause
          * significant delay in reading both clocksource and watchdog.
          *
          * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
          * report system busy, reinit the watchdog and skip the current
          * watchdog test.
          */
         wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
         wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
         if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
             goto skip_test;
     }
 
     pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
         smp_processor_id(), watchdog->name, wd_delay, nretries);
     return WD_READ_UNSTABLE;
 
 skip_test:
     pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
         smp_processor_id(), watchdog->name, wd_seq_delay);
     pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
         cs->name, wd_delay);
     return WD_READ_SKIP;
 }
 
 static u64 csnow_mid;
 static cpumask_t cpus_ahead;
 static cpumask_t cpus_behind;
 static cpumask_t cpus_chosen;
 
 static void clocksource_verify_choose_cpus(void)
 {
     int cpu, i, n = verify_n_cpus;
 
     if (n < 0) {
         /* Check all of the CPUs. */
         cpumask_copy(&cpus_chosen, cpu_online_mask);
         cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
         return;
     }
 
     /* If no checking desired, or no other CPU to check, leave. */
     cpumask_clear(&cpus_chosen);
     if (n == 0 || num_online_cpus() <= 1)
         return;
 
     /* Make sure to select at least one CPU other than the current CPU. */
     cpu = cpumask_first(cpu_online_mask);
     if (cpu == smp_processor_id())
         cpu = cpumask_next(cpu, cpu_online_mask);
     if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
         return;
     cpumask_set_cpu(cpu, &cpus_chosen);
 
     /* Force a sane value for the boot parameter. */
     if (n > nr_cpu_ids)
         n = nr_cpu_ids;
 
     /*
      * Randomly select the specified number of CPUs.  If the same
      * CPU is selected multiple times, that CPU is checked only once,
      * and no replacement CPU is selected.  This gracefully handles
      * situations where verify_n_cpus is greater than the number of
      * CPUs that are currently online.
      */
     for (i = 1; i < n; i++) {
         cpu = prandom_u32() % nr_cpu_ids;
         cpu = cpumask_next(cpu - 1, cpu_online_mask);
         if (cpu >= nr_cpu_ids)
             cpu = cpumask_first(cpu_online_mask);
         if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
             cpumask_set_cpu(cpu, &cpus_chosen);
     }
 
     /* Don't verify ourselves. */
     cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
 }
 
 static void clocksource_verify_one_cpu(void *csin)
 {
     struct clocksource *cs = (struct clocksource *)csin;
 
     csnow_mid = cs->read(cs);
 }
 
 void clocksource_verify_percpu(struct clocksource *cs)
 {
     int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
     u64 csnow_begin, csnow_end;
     int cpu, testcpu;
     s64 delta;
 
     if (verify_n_cpus == 0)
         return;
     cpumask_clear(&cpus_ahead);
     cpumask_clear(&cpus_behind);
     cpus_read_lock();
     preempt_disable();
     clocksource_verify_choose_cpus();
     if (cpumask_empty(&cpus_chosen)) {
         preempt_enable();
         cpus_read_unlock();
         pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
         return;
     }
     testcpu = smp_processor_id();
     pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
     for_each_cpu(cpu, &cpus_chosen) {
         if (cpu == testcpu)
             continue;
         csnow_begin = cs->read(cs);
         smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
         csnow_end = cs->read(cs);
         delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
         if (delta < 0)
             cpumask_set_cpu(cpu, &cpus_behind);
         delta = (csnow_end - csnow_mid) & cs->mask;
         if (delta < 0)
             cpumask_set_cpu(cpu, &cpus_ahead);
         delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
         cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
         if (cs_nsec > cs_nsec_max)
             cs_nsec_max = cs_nsec;
         if (cs_nsec < cs_nsec_min)
             cs_nsec_min = cs_nsec;
     }
     preempt_enable();
     cpus_read_unlock();
     if (!cpumask_empty(&cpus_ahead))
         pr_warn("        CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
             cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
     if (!cpumask_empty(&cpus_behind))
         pr_warn("        CPUs %*pbl behind CPU %d for clocksource %s.\n",
             cpumask_pr_args(&cpus_behind), testcpu, cs->name);
     if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
         pr_warn("        CPU %d check durations %lldns - %lldns for clocksource %s.\n",
             testcpu, cs_nsec_min, cs_nsec_max, cs->name);
 }
 EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
 
 static void clocksource_watchdog(struct timer_list *unused)
 {
     u64 csnow, wdnow, cslast, wdlast, delta;
     int next_cpu, reset_pending;
     int64_t wd_nsec, cs_nsec;
     struct clocksource *cs;
     enum wd_read_status read_ret;
     u32 md;
 
     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;
         }
 
         read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
 
         if (read_ret != WD_READ_SUCCESS) {
             if (read_ret == WD_READ_UNSTABLE)
                 /* Clock readout unreliable, so give it up. */
                 __clocksource_unstable(cs);
             continue;
         }
 
         /* 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. */
         md = cs->uncertainty_margin + watchdog->uncertainty_margin;
         if (abs(cs_nsec - wd_nsec) > md) {
             pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
                 smp_processor_id(), cs->name);
             pr_warn("                      '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
                 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
             pr_warn("                      '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
                 cs->name, cs_nsec, csnow, cslast, cs->mask);
             if (curr_clocksource == cs)
                 pr_warn("                      '%s' is current clocksource.\n", cs->name);
             else if (curr_clocksource)
                 pr_warn("                      '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
             else
                 pr_warn("                      No current clocksource.\n");
             __clocksource_unstable(cs);
             continue;
         }
 
         if (cs == curr_clocksource && cs->tick_stable)
             cs->tick_stable(cs);
 
         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);
 
     /*
      * Arm timer if not already pending: could race with concurrent
      * pair clocksource_stop_watchdog() clocksource_start_watchdog().
      */
     if (!timer_pending(&watchdog_timer)) {
         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;
     timer_setup(&watchdog_timer, clocksource_watchdog, 0);
     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)
 {
     INIT_LIST_HEAD(&cs->wd_list);
 
     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;
     }
 }
 
 static void clocksource_select_watchdog(bool fallback)
 {
     struct clocksource *cs, *old_wd;
     unsigned long flags;
 
     spin_lock_irqsave(&watchdog_lock, flags);
     /* save current watchdog */
     old_wd = watchdog;
     if (fallback)
         watchdog = NULL;
 
     list_for_each_entry(cs, &clocksource_list, list) {
         /* cs is a clocksource to be watched. */
         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
             continue;
 
         /* Skip current if we were requested for a fallback. */
         if (fallback && cs == old_wd)
             continue;
 
         /* Pick the best watchdog. */
         if (!watchdog || cs->rating > watchdog->rating)
             watchdog = cs;
     }
     /* If we failed to find a fallback restore the old one. */
     if (!watchdog)
         watchdog = old_wd;
 
     /* If we changed the watchdog we need to reset cycles. */
     if (watchdog != old_wd)
         clocksource_reset_watchdog();
 
     /* Check if the watchdog timer needs to be started. */
     clocksource_start_watchdog();
     spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
 static void clocksource_dequeue_watchdog(struct clocksource *cs)
 {
     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();
         }
     }
 }
 
 static int __clocksource_watchdog_kthread(void)
 {
     struct clocksource *cs, *tmp;
     unsigned long flags;
     int select = 0;
 
     /* Do any required per-CPU skew verification. */
     if (curr_clocksource &&
         curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
         curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
         clocksource_verify_percpu(curr_clocksource);
 
     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);
             __clocksource_change_rating(cs, 0);
             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);
 
     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 void clocksource_select_watchdog(bool fallback) { }
 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 static inline void clocksource_resume_watchdog(void) { }
 static inline int __clocksource_watchdog_kthread(void) { return 0; }
 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
 void clocksource_mark_unstable(struct clocksource *cs) { }
 
 static inline void clocksource_watchdog_lock(unsigned long *flags) { }
 static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
 
 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
 static bool clocksource_is_suspend(struct clocksource *cs)
 {
     return cs == suspend_clocksource;
 }
 
 static void __clocksource_suspend_select(struct clocksource *cs)
 {
     /*
      * Skip the clocksource which will be stopped in suspend state.
      */
     if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
         return;
 
     /*
      * The nonstop clocksource can be selected as the suspend clocksource to
      * calculate the suspend time, so it should not supply suspend/resume
      * interfaces to suspend the nonstop clocksource when system suspends.
      */
     if (cs->suspend || cs->resume) {
         pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
             cs->name);
     }
 
     /* Pick the best rating. */
     if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
         suspend_clocksource = cs;
 }
 
 /**
  * clocksource_suspend_select - Select the best clocksource for suspend timing
  * @fallback:   if select a fallback clocksource
  */
 static void clocksource_suspend_select(bool fallback)
 {
     struct clocksource *cs, *old_suspend;
 
     old_suspend = suspend_clocksource;
     if (fallback)
         suspend_clocksource = NULL;
 
     list_for_each_entry(cs, &clocksource_list, list) {
         /* Skip current if we were requested for a fallback. */
         if (fallback && cs == old_suspend)
             continue;
 
         __clocksource_suspend_select(cs);
     }
 }
 
 /**
  * clocksource_start_suspend_timing - Start measuring the suspend timing
  * @cs:         current clocksource from timekeeping
  * @start_cycles:   current cycles from timekeeping
  *
  * This function will save the start cycle values of suspend timer to calculate
  * the suspend time when resuming system.
  *
  * This function is called late in the suspend process from timekeeping_suspend(),
  * that means processes are frozen, non-boot cpus and interrupts are disabled
  * now. It is therefore possible to start the suspend timer without taking the
  * clocksource mutex.
  */
 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
 {
     if (!suspend_clocksource)
         return;
 
     /*
      * If current clocksource is the suspend timer, we should use the
      * tkr_mono.cycle_last value as suspend_start to avoid same reading
      * from suspend timer.
      */
     if (clocksource_is_suspend(cs)) {
         suspend_start = start_cycles;
         return;
     }
 
     if (suspend_clocksource->enable &&
         suspend_clocksource->enable(suspend_clocksource)) {
         pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
         return;
     }
 
     suspend_start = suspend_clocksource->read(suspend_clocksource);
 }
 
 /**
  * clocksource_stop_suspend_timing - Stop measuring the suspend timing
  * @cs:     current clocksource from timekeeping
  * @cycle_now:  current cycles from timekeeping
  *
  * This function will calculate the suspend time from suspend timer.
  *
  * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
  *
  * This function is called early in the resume process from timekeeping_resume(),
  * that means there is only one cpu, no processes are running and the interrupts
  * are disabled. It is therefore possible to stop the suspend timer without
  * taking the clocksource mutex.
  */
 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
 {
     u64 now, delta, nsec = 0;
 
     if (!suspend_clocksource)
         return 0;
 
     /*
      * If current clocksource is the suspend timer, we should use the
      * tkr_mono.cycle_last value from timekeeping as current cycle to
      * avoid same reading from suspend timer.
      */
     if (clocksource_is_suspend(cs))
         now = cycle_now;
     else
         now = suspend_clocksource->read(suspend_clocksource);
 
     if (now > suspend_start) {
         delta = clocksource_delta(now, suspend_start,
                       suspend_clocksource->mask);
         nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
                        suspend_clocksource->shift);
     }
 
     /*
      * Disable the suspend timer to save power if current clocksource is
      * not the suspend timer.
      */
     if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
         suspend_clocksource->disable(suspend_clocksource);
 
     return nsec;
 }
 
 /**
  * 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 than 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);
 }
 
 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;
 
     if (!strlen(override_name))
         goto found;
 
     /* 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. */
             if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
                 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
                     cs->name);
                 override_name[0] = 0;
             } else {
                 /*
                  * The override cannot be currently verified.
                  * Deferring to let the watchdog check.
                  */
                 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
                     cs->name);
             }
         } else
             /* Override clocksource can be used. */
             best = cs;
         break;
     }
 
 found:
     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)
 {
     __clocksource_select(false);
 }
 
 static void clocksource_select_fallback(void)
 {
     __clocksource_select(true);
 }
 
 /*
  * 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)
             break;
         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);
     }
 
     /*
      * If the uncertainty margin is not specified, calculate it.
      * If both scale and freq are non-zero, calculate the clock
      * period, but bound below at 2*WATCHDOG_MAX_SKEW.  However,
      * if either of scale or freq is zero, be very conservative and
      * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
      * uncertainty margin.  Allow stupidly small uncertainty margins
      * to be specified by the caller for testing purposes, but warn
      * to discourage production use of this capability.
      */
     if (scale && freq && !cs->uncertainty_margin) {
         cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
         if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
             cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
     } else if (!cs->uncertainty_margin) {
         cs->uncertainty_margin = WATCHDOG_THRESHOLD;
     }
     WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
 
     /*
      * 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("%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)
 {
     unsigned long flags;
 
     clocksource_arch_init(cs);
 
     if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
         cs->id = CSID_GENERIC;
     if (cs->vdso_clock_mode < 0 ||
         cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
         pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
             cs->name, cs->vdso_clock_mode);
         cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
     }
 
     /* 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_watchdog_lock(&flags);
     clocksource_enqueue(cs);
     clocksource_enqueue_watchdog(cs);
     clocksource_watchdog_unlock(&flags);
 
     clocksource_select();
     clocksource_select_watchdog(false);
     __clocksource_suspend_select(cs);
     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)
 {
     unsigned long flags;
 
     mutex_lock(&clocksource_mutex);
     clocksource_watchdog_lock(&flags);
     __clocksource_change_rating(cs, rating);
     clocksource_watchdog_unlock(&flags);
 
     clocksource_select();
     clocksource_select_watchdog(false);
     clocksource_suspend_select(false);
     mutex_unlock(&clocksource_mutex);
 }
 EXPORT_SYMBOL(clocksource_change_rating);
 
 /*
  * Unbind clocksource @cs. Called with clocksource_mutex held
  */
 static int clocksource_unbind(struct clocksource *cs)
 {
     unsigned long flags;
 
     if (clocksource_is_watchdog(cs)) {
         /* Select and try to install a replacement watchdog. */
         clocksource_select_watchdog(true);
         if (clocksource_is_watchdog(cs))
             return -EBUSY;
     }
 
     if (cs == curr_clocksource) {
         /* Select and try to install a replacement clock source */
         clocksource_select_fallback();
         if (curr_clocksource == cs)
             return -EBUSY;
     }
 
     if (clocksource_is_suspend(cs)) {
         /*
          * Select and try to install a replacement suspend clocksource.
          * If no replacement suspend clocksource, we will just let the
          * clocksource go and have no suspend clocksource.
          */
         clocksource_suspend_select(true);
     }
 
     clocksource_watchdog_lock(&flags);
     clocksource_dequeue_watchdog(cs);
     list_del_init(&cs->list);
     clocksource_watchdog_unlock(&flags);
 
     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
 /**
  * current_clocksource_show - 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 current_clocksource_show(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;
 }
 
 /**
  * current_clocksource_store - 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 current_clocksource_store(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;
 }
 static DEVICE_ATTR_RW(current_clocksource);
 
 /**
  * unbind_clocksource_store - 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 unbind_clocksource_store(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;
 }
 static DEVICE_ATTR_WO(unbind_clocksource);
 
 /**
  * available_clocksource_show - 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 available_clocksource_show(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;
 }
 static DEVICE_ATTR_RO(available_clocksource);
 
 static struct attribute *clocksource_attrs[] = {
     &dev_attr_current_clocksource.attr,
     &dev_attr_unbind_clocksource.attr,
     &dev_attr_available_clocksource.attr,
     NULL
 };
 ATTRIBUTE_GROUPS(clocksource);
 
 static struct bus_type clocksource_subsys = {
     .name = "clocksource",
     .dev_name = "clocksource",
 };
 
 static struct device device_clocksource = {
     .id = 0,
     .bus    = &clocksource_subsys,
     .groups = clocksource_groups,
 };
 
 static int __init init_clocksource_sysfs(void)
 {
     int error = subsys_system_register(&clocksource_subsys, NULL);
 
     if (!error)
         error = device_register(&device_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")) {
         pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
         return boot_override_clocksource("acpi_pm");
     }
     pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
     return boot_override_clocksource(str);
 }
 
 __setup("clock=", boot_override_clock);

This page was automatically generated by the 2.1.0 LXR engine. The LXR team