LXR linux/arch/mips/kernel/time.c

   1/*
   2 * Copyright 2001 MontaVista Software Inc.
   3 * Author: Jun Sun, jsun@mvista.com or jsun@junsun.net
   4 * Copyright (c) 2003, 2004  Maciej W. Rozycki
   5 *
   6 * Common time service routines for MIPS machines.
   7 *
   8 * This program is free software; you can redistribute  it and/or modify it
   9 * under  the terms of  the GNU General  Public License as published by the
  10 * Free Software Foundation;  either version 2 of the  License, or (at your
  11 * option) any later version.
  12 */
  13#include <linux/bug.h>
  14#include <linux/clockchips.h>
  15#include <linux/types.h>
  16#include <linux/kernel.h>
  17#include <linux/init.h>
  18#include <linux/sched.h>
  19#include <linux/param.h>
  20#include <linux/time.h>
  21#include <linux/timex.h>
  22#include <linux/smp.h>
  23#include <linux/spinlock.h>
  24#include <linux/export.h>
  25
  26#include <asm/cpu-features.h>
  27#include <asm/cpu-type.h>
  28#include <asm/div64.h>
  29#include <asm/time.h>
  30
  31/*
  32 * forward reference
  33 */
  34DEFINE_SPINLOCK(rtc_lock);
  35EXPORT_SYMBOL(rtc_lock);
  36
  37static int null_perf_irq(void)
  38{
  39        return 0;
  40}
  41
  42int (*perf_irq)(void) = null_perf_irq;
  43
  44EXPORT_SYMBOL(perf_irq);
  45
  46/*
  47 * time_init() - it does the following things.
  48 *
  49 * 1) plat_time_init() -
  50 *      a) (optional) set up RTC routines,
  51 *      b) (optional) calibrate and set the mips_hpt_frequency
  52 *          (only needed if you intended to use cpu counter as timer interrupt
  53 *           source)
  54 * 2) calculate a couple of cached variables for later usage
  55 */
  56
  57unsigned int mips_hpt_frequency;
  58EXPORT_SYMBOL_GPL(mips_hpt_frequency);
  59
  60static __init int cpu_has_mfc0_count_bug(void)
  61{
  62        switch (current_cpu_type()) {
  63        case CPU_R4000PC:
  64        case CPU_R4000SC:
  65        case CPU_R4000MC:
  66                /*
  67                 * V3.0 is documented as suffering from the mfc0 from count bug.
  68                 * Afaik this is the last version of the R4000.  Later versions
  69                 * were marketed as R4400.
  70                 */
  71                return 1;
  72
  73        case CPU_R4400PC:
  74        case CPU_R4400SC:
  75        case CPU_R4400MC:
  76                /*
  77                 * The published errata for the R4400 up to 3.0 say the CPU
  78                 * has the mfc0 from count bug.
  79                 */
  80                if ((current_cpu_data.processor_id & 0xff) <= 0x30)
  81                        return 1;
  82
  83                /*
  84                 * we assume newer revisions are ok
  85                 */
  86                return 0;
  87        }
  88
  89        return 0;
  90}
  91
  92void __init time_init(void)
  93{
  94        plat_time_init();
  95
  96        /*
  97         * The use of the R4k timer as a clock event takes precedence;
  98         * if reading the Count register might interfere with the timer
  99         * interrupt, then we don't use the timer as a clock source.
 100         * We may still use the timer as a clock source though if the
 101         * timer interrupt isn't reliable; the interference doesn't
 102         * matter then, because we don't use the interrupt.
 103         */
 104        if (mips_clockevent_init() != 0 || !cpu_has_mfc0_count_bug())
 105                init_mips_clocksource();
 106}
 107