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