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  */
  34 DEFINE_SPINLOCK(rtc_lock);
  35 EXPORT_SYMBOL(rtc_lock);
  36
  37 static int null_perf_irq(void)
  38 {
  39         return 0;
  40 }
  41
  42 int (*perf_irq)(void) = null_perf_irq;
  43
  44 EXPORT_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
  57 unsigned int mips_hpt_frequency;
  58 EXPORT_SYMBOL_GPL(mips_hpt_frequency);
  59
  60 static __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
  92 void __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 }