cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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jiffies.c (2666B)

      1// SPDX-License-Identifier: GPL-2.0+
      2/*
      3 * This file contains the jiffies based clocksource.
      4 *
      5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
      6 */
      7#include <linux/clocksource.h>
      8#include <linux/jiffies.h>
      9#include <linux/module.h>
     10#include <linux/init.h>
     11
     12#include "timekeeping.h"
     13#include "tick-internal.h"
     14
     15
     16static u64 jiffies_read(struct clocksource *cs)
     17{
     18	return (u64) jiffies;
     19}
     20
     21/*
     22 * The Jiffies based clocksource is the lowest common
     23 * denominator clock source which should function on
     24 * all systems. It has the same coarse resolution as
     25 * the timer interrupt frequency HZ and it suffers
     26 * inaccuracies caused by missed or lost timer
     27 * interrupts and the inability for the timer
     28 * interrupt hardware to accurately tick at the
     29 * requested HZ value. It is also not recommended
     30 * for "tick-less" systems.
     31 */
     32static struct clocksource clocksource_jiffies = {
     33	.name			= "jiffies",
     34	.rating			= 1, /* lowest valid rating*/
     35	.uncertainty_margin	= 32 * NSEC_PER_MSEC,
     36	.read			= jiffies_read,
     37	.mask			= CLOCKSOURCE_MASK(32),
     38	.mult			= TICK_NSEC << JIFFIES_SHIFT, /* details above */
     39	.shift			= JIFFIES_SHIFT,
     40	.max_cycles		= 10,
     41};
     42
     43__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
     44__cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq =
     45	SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock);
     46
     47#if (BITS_PER_LONG < 64)
     48u64 get_jiffies_64(void)
     49{
     50	unsigned int seq;
     51	u64 ret;
     52
     53	do {
     54		seq = read_seqcount_begin(&jiffies_seq);
     55		ret = jiffies_64;
     56	} while (read_seqcount_retry(&jiffies_seq, seq));
     57	return ret;
     58}
     59EXPORT_SYMBOL(get_jiffies_64);
     60#endif
     61
     62EXPORT_SYMBOL(jiffies);
     63
     64static int __init init_jiffies_clocksource(void)
     65{
     66	return __clocksource_register(&clocksource_jiffies);
     67}
     68
     69core_initcall(init_jiffies_clocksource);
     70
     71struct clocksource * __init __weak clocksource_default_clock(void)
     72{
     73	return &clocksource_jiffies;
     74}
     75
     76static struct clocksource refined_jiffies;
     77
     78int register_refined_jiffies(long cycles_per_second)
     79{
     80	u64 nsec_per_tick, shift_hz;
     81	long cycles_per_tick;
     82
     83
     84
     85	refined_jiffies = clocksource_jiffies;
     86	refined_jiffies.name = "refined-jiffies";
     87	refined_jiffies.rating++;
     88
     89	/* Calc cycles per tick */
     90	cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
     91	/* shift_hz stores hz<<8 for extra accuracy */
     92	shift_hz = (u64)cycles_per_second << 8;
     93	shift_hz += cycles_per_tick/2;
     94	do_div(shift_hz, cycles_per_tick);
     95	/* Calculate nsec_per_tick using shift_hz */
     96	nsec_per_tick = (u64)NSEC_PER_SEC << 8;
     97	nsec_per_tick += (u32)shift_hz/2;
     98	do_div(nsec_per_tick, (u32)shift_hz);
     99
    100	refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
    101
    102	__clocksource_register(&refined_jiffies);
    103	return 0;
    104}