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- // SPDX-License-Identifier: GPL-2.0+
- /*
- * This file contains the jiffies based clocksource.
- *
- * Copyright (C) 2004, 2005 IBM, John Stultz ([email protected])
- */
- #include <linux/clocksource.h>
- #include <linux/jiffies.h>
- #include <linux/module.h>
- #include <linux/init.h>
- #include "timekeeping.h"
- #include "tick-internal.h"
- static u64 jiffies_read(struct clocksource *cs)
- {
- return (u64) jiffies;
- }
- /*
- * The Jiffies based clocksource is the lowest common
- * denominator clock source which should function on
- * all systems. It has the same coarse resolution as
- * the timer interrupt frequency HZ and it suffers
- * inaccuracies caused by missed or lost timer
- * interrupts and the inability for the timer
- * interrupt hardware to accurately tick at the
- * requested HZ value. It is also not recommended
- * for "tick-less" systems.
- */
- static struct clocksource clocksource_jiffies = {
- .name = "jiffies",
- .rating = 1, /* lowest valid rating*/
- .uncertainty_margin = 32 * NSEC_PER_MSEC,
- .read = jiffies_read,
- .mask = CLOCKSOURCE_MASK(32),
- .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
- .shift = JIFFIES_SHIFT,
- .max_cycles = 10,
- };
- __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
- __cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq =
- SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock);
- #if (BITS_PER_LONG < 64)
- u64 get_jiffies_64(void)
- {
- unsigned int seq;
- u64 ret;
- do {
- seq = read_seqcount_begin(&jiffies_seq);
- ret = jiffies_64;
- } while (read_seqcount_retry(&jiffies_seq, seq));
- return ret;
- }
- EXPORT_SYMBOL(get_jiffies_64);
- #endif
- EXPORT_SYMBOL(jiffies);
- static int __init init_jiffies_clocksource(void)
- {
- return __clocksource_register(&clocksource_jiffies);
- }
- core_initcall(init_jiffies_clocksource);
- struct clocksource * __init __weak clocksource_default_clock(void)
- {
- return &clocksource_jiffies;
- }
- static struct clocksource refined_jiffies;
- int register_refined_jiffies(long cycles_per_second)
- {
- u64 nsec_per_tick, shift_hz;
- long cycles_per_tick;
- refined_jiffies = clocksource_jiffies;
- refined_jiffies.name = "refined-jiffies";
- refined_jiffies.rating++;
- /* Calc cycles per tick */
- cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
- /* shift_hz stores hz<<8 for extra accuracy */
- shift_hz = (u64)cycles_per_second << 8;
- shift_hz += cycles_per_tick/2;
- do_div(shift_hz, cycles_per_tick);
- /* Calculate nsec_per_tick using shift_hz */
- nsec_per_tick = (u64)NSEC_PER_SEC << 8;
- nsec_per_tick += (u32)shift_hz/2;
- do_div(nsec_per_tick, (u32)shift_hz);
- refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
- __clocksource_register(&refined_jiffies);
- return 0;
- }
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