arch/mips/kernel/time.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright 2001 MontaVista Software Inc.
   4  * Author: Jun Sun, jsun@mvista.com or jsun@junsun.net
   5  * Copyright (c) 2003, 2004  Maciej W. Rozycki
   6  *
   7  * Common time service routines for MIPS machines.
   8  */
   9 #include <linux/bug.h>
  10 #include <linux/clockchips.h>
  11 #include <linux/types.h>
  12 #include <linux/kernel.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/param.h>
  16 #include <linux/time.h>
  17 #include <linux/timex.h>
  18 #include <linux/smp.h>
  19 #include <linux/spinlock.h>
  20 #include <linux/export.h>
  21
  22 #include <asm/cpu-features.h>
  23 #include <asm/cpu-type.h>
  24 #include <asm/div64.h>
  25 #include <asm/time.h>
  26
  27 /*
  28  * forward reference
  29  */
  30 DEFINE_SPINLOCK(rtc_lock);
  31 EXPORT_SYMBOL(rtc_lock);
  32
  33 static int null_perf_irq(void)
  34 {
  35         return 0;
  36 }
  37
  38 int (*perf_irq)(void) = null_perf_irq;
  39
  40 EXPORT_SYMBOL(perf_irq);
  41
  42 /*
  43  * time_init() - it does the following things.
  44  *
  45  * 1) plat_time_init() -
  46  *      a) (optional) set up RTC routines,
  47  *      b) (optional) calibrate and set the mips_hpt_frequency
  48  *          (only needed if you intended to use cpu counter as timer interrupt
  49  *           source)
  50  * 2) calculate a couple of cached variables for later usage
  51  */
  52
  53 unsigned int mips_hpt_frequency;
  54 EXPORT_SYMBOL_GPL(mips_hpt_frequency);
  55
  56 static __init int cpu_has_mfc0_count_bug(void)
  57 {
  58         switch (current_cpu_type()) {
  59         case CPU_R4000PC:
  60         case CPU_R4000SC:
  61         case CPU_R4000MC:
  62                 /*
  63                  * V3.0 is documented as suffering from the mfc0 from count bug.
  64                  * Afaik this is the last version of the R4000.  Later versions
  65                  * were marketed as R4400.
  66                  */
  67                 return 1;
  68
  69         case CPU_R4400PC:
  70         case CPU_R4400SC:
  71         case CPU_R4400MC:
  72                 /*
  73                  * The published errata for the R4400 up to 3.0 say the CPU
  74                  * has the mfc0 from count bug.
  75                  */
  76                 if ((current_cpu_data.processor_id & 0xff) <= 0x30)
  77                         return 1;
  78
  79                 /*
  80                  * we assume newer revisions are ok
  81                  */
  82                 return 0;
  83         }
  84
  85         return 0;
  86 }
  87
  88 void __init time_init(void)
  89 {
  90         plat_time_init();
  91
  92         /*
  93          * The use of the R4k timer as a clock event takes precedence;
  94          * if reading the Count register might interfere with the timer
  95          * interrupt, then we don't use the timer as a clock source.
  96          * We may still use the timer as a clock source though if the
  97          * timer interrupt isn't reliable; the interference doesn't
  98          * matter then, because we don't use the interrupt.
  99          */
 100         if (mips_clockevent_init() != 0 || !cpu_has_mfc0_count_bug())
 101                 init_mips_clocksource();
 102 }