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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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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/clocksource.h>#include <linux/cpu.h>#include <linux/delay.h>#include <linux/device.h>#include <linux/init.h>#include <linux/kthread.h>#include <linux/module.h>#include <linux/prandom.h>#include <linux/sched.h>#include <linux/tick.h>#include <linux/topology.h>
#include "tick-internal.h"#include "timekeeping_internal.h"
static void clocksource_enqueue(struct clocksource *cs);
static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end){ u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta);
if (likely(delta < cs->max_cycles)) return clocksource_cyc2ns(delta, cs->mult, cs->shift);
return mul_u64_u32_shr(delta, cs->mult, cs->shift);}
/** * 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. */voidclocks_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;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOGstatic 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;
/* Watchdog interval: 0.5sec. */#define WATCHDOG_INTERVAL (HZ >> 1)#define WATCHDOG_INTERVAL_NS (WATCHDOG_INTERVAL * (NSEC_PER_SEC / HZ))
/* Maximum time between two reference watchdog readouts */#define WATCHDOG_READOUT_MAX_NS (50U * NSEC_PER_USEC)
/* * Maximum time between two remote readouts for NUMA=n. On NUMA enabled systems * the timeout is calculated from the numa distance. */#define WATCHDOG_DEFAULT_TIMEOUT_NS (50U * NSEC_PER_USEC)
/* * Remote timeout NUMA distance multiplier. The local distance is 10. The * default remote distance is 20. ACPI tables provide more accurate numbers * which are guaranteed to be greater than the local distance. * * This results in a 5us base value, which is equivalent to the above !NUMA * default. */#define WATCHDOG_NUMA_MULTIPLIER_NS ((u64)(WATCHDOG_DEFAULT_TIMEOUT_NS / LOCAL_DISTANCE))
/* Limit the NUMA timeout in case the distance values are insanely big */#define WATCHDOG_NUMA_MAX_TIMEOUT_NS ((u64)(500U * NSEC_PER_USEC))
/* Shift values to calculate the approximate $N ppm of a given delta. */#define SHIFT_500PPM 11#define SHIFT_4000PPM 8
/* Number of attempts to read the watchdog */#define WATCHDOG_FREQ_RETRIES 3
/* Five reads local and remote for inter CPU skew detection */#define WATCHDOG_REMOTE_MAX_SEQ 10
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_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_change_rating(struct clocksource *cs, int rating){ list_del(&cs->list); cs->rating = rating; clocksource_enqueue(cs);}
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);}
static inline void clocksource_reset_watchdog(void){ struct clocksource *cs;
list_for_each_entry(cs, &watchdog_list, wd_list) cs->flags &= ~CLOCK_SOURCE_WATCHDOG;}
enum wd_result { WD_SUCCESS, WD_FREQ_NO_WATCHDOG, WD_FREQ_TIMEOUT, WD_FREQ_RESET, WD_FREQ_SKEWED, WD_CPU_TIMEOUT, WD_CPU_SKEWED,};
struct watchdog_cpu_data { /* Keep first as it is 32 byte aligned */ call_single_data_t csd; atomic_t remote_inprogress; enum wd_result result; u64 cpu_ts[2]; struct clocksource *cs; /* Ensure that the sequence is in a separate cache line */ atomic_t seq ____cacheline_aligned; /* Set by the control CPU according to NUMA distance */ u64 timeout_ns;};
struct watchdog_data { raw_spinlock_t lock; enum wd_result result;
u64 wd_seq; u64 wd_delta; u64 cs_delta; u64 cpu_ts[2];
unsigned int curr_cpu;} ____cacheline_aligned_in_smp;
static void watchdog_check_skew_remote(void *unused);
static DEFINE_PER_CPU_ALIGNED(struct watchdog_cpu_data, watchdog_cpu_data) = { .csd = CSD_INIT(watchdog_check_skew_remote, NULL),};
static struct watchdog_data watchdog_data = { .lock = __RAW_SPIN_LOCK_UNLOCKED(watchdog_data.lock),};
static inline void watchdog_set_result(struct watchdog_cpu_data *wd, enum wd_result result){ guard(raw_spinlock)(&watchdog_data.lock); if (!wd->result) { atomic_set(&wd->seq, WATCHDOG_REMOTE_MAX_SEQ); WRITE_ONCE(wd->result, result); }}
/* Wait for the sequence number to hand over control. */static bool watchdog_wait_seq(struct watchdog_cpu_data *wd, u64 start, int seq){ for(int cnt = 0; atomic_read(&wd->seq) < seq; cnt++) { /* Bail if the other side set an error result */ if (READ_ONCE(wd->result) != WD_SUCCESS) return false;
/* Prevent endless loops if the other CPU does not react. */ if (cnt == 5000) { u64 nsecs = ktime_get_raw_fast_ns();
if (nsecs - start >=wd->timeout_ns) { watchdog_set_result(wd, WD_CPU_TIMEOUT); return false; } cnt = 0; } cpu_relax(); } return seq < WATCHDOG_REMOTE_MAX_SEQ;}
static void watchdog_check_skew(struct watchdog_cpu_data *wd, int index){ u64 prev, now, delta, start = ktime_get_raw_fast_ns(); int local = index, remote = (index + 1) & 0x1; struct clocksource *cs = wd->cs;
/* Set the local timestamp so that the first iteration works correctly */ wd->cpu_ts[local] = cs->read(cs);
/* Signal arrival */ atomic_inc(&wd->seq);
for (int seq = local + 2; seq < WATCHDOG_REMOTE_MAX_SEQ; seq += 2) { if (!watchdog_wait_seq(wd, start, seq)) return;
/* Capture local timestamp before possible non-local coherency overhead */ now = cs->read(cs);
/* Store local timestamp before reading remote to limit coherency stalls */ wd->cpu_ts[local] = now;
prev = wd->cpu_ts[remote]; delta = (now - prev) & cs->mask;
if (delta > cs->max_raw_delta) { watchdog_set_result(wd, WD_CPU_SKEWED); return; }
/* Hand over to the remote CPU */ atomic_inc(&wd->seq); }}
static void watchdog_check_skew_remote(void *unused){ struct watchdog_cpu_data *wd = this_cpu_ptr(&watchdog_cpu_data);
atomic_inc(&wd->remote_inprogress); watchdog_check_skew(wd, 1); atomic_dec(&wd->remote_inprogress);}
static inline bool wd_csd_locked(struct watchdog_cpu_data *wd){ return READ_ONCE(wd->csd.node.u_flags) & CSD_FLAG_LOCK;}
/* * This is only invoked for remote CPUs. See watchdog_check_cpu_skew(). */static inline u64 wd_get_remote_timeout(unsigned int remote_cpu){ unsigned int n1, n2; u64 ns;
if (nr_node_ids == 1) return WATCHDOG_DEFAULT_TIMEOUT_NS;
n1 = cpu_to_node(smp_processor_id()); n2 = cpu_to_node(remote_cpu); ns = WATCHDOG_NUMA_MULTIPLIER_NS * node_distance(n1, n2); return min(ns, WATCHDOG_NUMA_MAX_TIMEOUT_NS);}
static void __watchdog_check_cpu_skew(struct clocksource *cs, unsigned int cpu){ struct watchdog_cpu_data *wd;
wd = per_cpu_ptr(&watchdog_cpu_data, cpu); if (atomic_read(&wd->remote_inprogress) || wd_csd_locked(wd)) { watchdog_data.result = WD_CPU_TIMEOUT; return; }
atomic_set(&wd->seq, 0); wd->result = WD_SUCCESS; wd->cs = cs; /* Store the current CPU ID for the watchdog test unit */ cs->wd_cpu = smp_processor_id();
wd->timeout_ns = wd_get_remote_timeout(cpu);
/* Kick the remote CPU into the watchdog function */ if (WARN_ON_ONCE(smp_call_function_single_async(cpu, &wd->csd))) { watchdog_data.result = WD_CPU_TIMEOUT; return; }
scoped_guard(irq) watchdog_check_skew(wd, 0);
scoped_guard(raw_spinlock_irq, &watchdog_data.lock) { watchdog_data.result = wd->result; memcpy(watchdog_data.cpu_ts, wd->cpu_ts, sizeof(wd->cpu_ts)); }}
static void watchdog_check_cpu_skew(struct clocksource *cs){ unsigned int cpu = watchdog_data.curr_cpu;
cpu = cpumask_next_wrap(cpu, cpu_online_mask); watchdog_data.curr_cpu = cpu;
/* Skip the current CPU. Handles num_online_cpus() == 1 as well */ if (cpu == smp_processor_id()) return;
/* Don't interfere with the test mechanics */ if ((cs->flags & CLOCK_SOURCE_WDTEST) && !(cs->flags & CLOCK_SOURCE_WDTEST_PERCPU)) return;
__watchdog_check_cpu_skew(cs, cpu);}
static bool watchdog_check_freq(struct clocksource *cs, bool reset_pending){ unsigned int ppm_shift = SHIFT_4000PPM; u64 wd_ts0, wd_ts1, cs_ts;
watchdog_data.result = WD_SUCCESS; if (!watchdog) { watchdog_data.result = WD_FREQ_NO_WATCHDOG; return false; }
if (cs->flags & CLOCK_SOURCE_WDTEST_PERCPU) return true;
/* * If both the clocksource and the watchdog claim they are * calibrated use 500ppm limit. Uncalibrated clocksources need a * larger allowance because thefirmware supplied frequencies can be * way off. */ if (watchdog->flags & CLOCK_SOURCE_CALIBRATED && cs->flags & CLOCK_SOURCE_CALIBRATED) ppm_shift = SHIFT_500PPM;
for (int retries = 0; retries < WATCHDOG_FREQ_RETRIES; retries++) { s64 wd_last, cs_last, wd_seq, wd_delta, cs_delta, max_delta;
scoped_guard(irq) { wd_ts0 = watchdog->read(watchdog); cs_ts = cs->read(cs); wd_ts1 = watchdog->read(watchdog); }
wd_last = cs->wd_last; cs_last = cs->cs_last;
/* Validate the watchdog readout window */ wd_seq = cycles_to_nsec_safe(watchdog, wd_ts0, wd_ts1); if (wd_seq > WATCHDOG_READOUT_MAX_NS) { /* Store for printout in case all retries fail */ watchdog_data.wd_seq = wd_seq; continue; }
/* Store for subsequent processing */ cs->wd_last = wd_ts0; cs->cs_last = cs_ts;
/* First round or reset pending? */ if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || reset_pending) goto reset;
/* Calculate the nanosecond deltas from the last invocation */ wd_delta = cycles_to_nsec_safe(watchdog, wd_last, wd_ts0); cs_delta = cycles_to_nsec_safe(cs, cs_last, cs_ts);
watchdog_data.wd_delta = wd_delta; watchdog_data.cs_delta = cs_delta;
/* * Ensure that the deltas are within the readout limits of * the clocksource and the watchdog. Long delays can cause * clocksources to overflow. */ max_delta = max(wd_delta, cs_delta); if (max_delta > cs->max_idle_ns || max_delta > watchdog->max_idle_ns) goto reset;
/* * Calculate and validate the skew against the allowed PPM * value of the maximum delta plus the watchdog readout * time. */ if (abs(wd_delta - cs_delta) < (max_delta >> ppm_shift) + wd_seq) return true;
watchdog_data.result = WD_FREQ_SKEWED; return false; }
watchdog_data.result = WD_FREQ_TIMEOUT; return false;
reset: cs->flags |= CLOCK_SOURCE_WATCHDOG; watchdog_data.result = WD_FREQ_RESET; return false;}
/* Synchronization for sched clock */static void clocksource_tick_stable(struct clocksource *cs){ if (cs == curr_clocksource && cs->tick_stable) cs->tick_stable(cs);}
/* Conditionaly enable high resolution mode */static void clocksource_enable_highres(struct clocksource *cs){ if ((cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) || !(cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) || !watchdog || !(watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) return;
/* Mark it valid for high-res. */ cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
/* * Can't schedule work before finished_booting is * true. clocksource_done_booting will take care of it. */ if (!finished_booting) return;
if (cs->flags & CLOCK_SOURCE_WDTEST) return;
/* * 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(); }}
static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 2);
static void watchdog_print_freq_timeout(struct clocksource *cs){ if (!__ratelimit(&ratelimit_state)) return; pr_info("Watchdog %s read timed out. Readout sequence took: %lluns\n", watchdog->name, watchdog_data.wd_seq);}
static void watchdog_print_freq_skew(struct clocksource *cs){ pr_warn("Marking clocksource %s unstable due to frequency skew\n", cs->name); pr_warn("Watchdog %20s interval: %16lluns\n", watchdog->name, watchdog_data.wd_delta); pr_warn("Clocksource %20s interval: %16lluns\n", cs->name, watchdog_data.cs_delta);}
static void watchdog_handle_remote_timeout(struct clocksource *cs){ pr_info_once("Watchdog remote CPU %u read timed out\n", watchdog_data.curr_cpu);}
static void watchdog_print_remote_skew(struct clocksource *cs){ pr_warn("Marking clocksource %s unstable due to inter CPU skew\n", cs->name); if (watchdog_data.cpu_ts[0] < watchdog_data.cpu_ts[1]) { pr_warn("CPU%u %16llu < CPU%u %16llu (cycles)\n", smp_processor_id(), watchdog_data.cpu_ts[0], watchdog_data.curr_cpu, watchdog_data.cpu_ts[1]); } else { pr_warn("CPU%u %16llu < CPU%u %16llu (cycles)\n", watchdog_data.curr_cpu, watchdog_data.cpu_ts[1], smp_processor_id(), watchdog_data.cpu_ts[0]); }}
static void watchdog_check_result(struct clocksource *cs){ switch (watchdog_data.result) { case WD_SUCCESS: clocksource_tick_stable(cs); clocksource_enable_highres(cs); return;
case WD_FREQ_TIMEOUT: watchdog_print_freq_timeout(cs); /* Try again later and invalidate the reference timestamps. */ cs->flags &= ~CLOCK_SOURCE_WATCHDOG; return;
case WD_FREQ_NO_WATCHDOG: case WD_FREQ_RESET: /* * Nothing to do when the reference timestamps were reset * or no watchdog clocksource registered. */ return;
case WD_FREQ_SKEWED: watchdog_print_freq_skew(cs); break;
case WD_CPU_TIMEOUT: /* Remote check timed out. Try again next cycle. */ watchdog_handle_remote_timeout(cs); return;
case WD_CPU_SKEWED: watchdog_print_remote_skew(cs); break; } __clocksource_unstable(cs);}
static void clocksource_watchdog(struct timer_list *unused){ struct clocksource *cs; bool reset_pending;
guard(spinlock)(&watchdog_lock); if (!watchdog_running) return;
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; }
/* Compare against watchdog clocksource if available */ if (watchdog_check_freq(cs, reset_pending)) { /* Check for inter CPU skew */ watchdog_check_cpu_skew(cs); }
watchdog_check_result(cs); }
/* Clear after the full clocksource walk */ if (reset_pending) atomic_dec(&watchdog_reset_pending);
/* Could have been rearmed by a stop/start cycle */ if (!timer_pending(&watchdog_timer)) { watchdog_timer.expires += WATCHDOG_INTERVAL; add_timer_local(&watchdog_timer); }}
static inline void clocksource_start_watchdog(void){ if (watchdog_running || list_empty(&watchdog_list)) return; timer_setup(&watchdog_timer, clocksource_watchdog, TIMER_PINNED); watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, get_boot_cpu_id()); watchdog_running = 1;}
static inline void clocksource_stop_watchdog(void){ if (!watchdog_running || !list_empty(&watchdog_list)) return; timer_delete(&watchdog_timer); watchdog_running = 0;}
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;
/* * If it's not continuous, don't put the fox in charge of * the henhouse. */ if (!(cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)) 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;
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, 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) nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now);
/* * 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);
/* * Threshold for detecting negative motion in clocksource_delta(). * * Allow for 0.875 of the counter width so that overly long idle * sleeps, which go slightly over mask/2, do not trigger the * negative motion detection. */ cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);}
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; if (cs->flags & CLOCK_SOURCE_WDTEST) 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; if (cs->flags & CLOCK_SOURCE_WDTEST) 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 */static 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);
/* Update cs::freq_khz */ cs->freq_khz = div_u64((u64)freq * scale, 1000); }
/* * 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);}
/** * __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 (WARN_ON_ONCE(!freq && cs->flags & CLOCK_SOURCE_HAS_COUPLED_CLOCK_EVENT)) cs->flags &= ~CLOCK_SOURCE_HAS_COUPLED_CLOCK_EVENT;
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 __devm_clocksource_unregister(void *data){ struct clocksource *cs = data;
clocksource_unregister(cs);}
int __devm_clocksource_register_scale(struct device *dev, struct clocksource *cs, u32 scale, u32 freq){ int ret;
ret = __clocksource_register_scale(cs, scale, freq); if (ret) return ret;
return devm_add_action_or_reset(dev, __devm_clocksource_unregister, cs);}EXPORT_SYMBOL_GPL(__devm_clocksource_register_scale);
/* * 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 = sysfs_emit(buf, "%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 const 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) strscpy(override_name, str); 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);