arch/mips/kernel/csrc-r4k.c

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 2007 by Ralf Baechle
   7  */
   8 #include <linux/clocksource.h>
   9 #include <linux/cpufreq.h>
  10 #include <linux/init.h>
  11 #include <linux/sched_clock.h>
  12
  13 #include <asm/time.h>
  14
  15 static u64 c0_hpt_read(struct clocksource *cs)
  16 {
  17         return read_c0_count();
  18 }
  19
  20 static struct clocksource clocksource_mips = {
  21         .name           = "MIPS",
  22         .read           = c0_hpt_read,
  23         .mask           = CLOCKSOURCE_MASK(32),
  24         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  25 };
  26
  27 static u64 __maybe_unused notrace r4k_read_sched_clock(void)
  28 {
  29         return read_c0_count();
  30 }
  31
  32 static inline unsigned int rdhwr_count(void)
  33 {
  34         unsigned int count;
  35
  36         __asm__ __volatile__(
  37         "       .set push\n"
  38         "       .set mips32r2\n"
  39         "       rdhwr   %0, $2\n"
  40         "       .set pop\n"
  41         : "=r" (count));
  42
  43         return count;
  44 }
  45
  46 static bool rdhwr_count_usable(void)
  47 {
  48         unsigned int prev, curr, i;
  49
  50         /*
  51          * Older QEMUs have a broken implementation of RDHWR for the CP0 count
  52          * which always returns a constant value. Try to identify this and don't
  53          * use it in the VDSO if it is broken. This workaround can be removed
  54          * once the fix has been in QEMU stable for a reasonable amount of time.
  55          */
  56         for (i = 0, prev = rdhwr_count(); i < 100; i++) {
  57                 curr = rdhwr_count();
  58
  59                 if (curr != prev)
  60                         return true;
  61
  62                 prev = curr;
  63         }
  64
  65         pr_warn("Not using R4K clocksource in VDSO due to broken RDHWR\n");
  66         return false;
  67 }
  68
  69 #ifdef CONFIG_CPU_FREQ
  70
  71 static bool __read_mostly r4k_clock_unstable;
  72
  73 static void r4k_clocksource_unstable(char *reason)
  74 {
  75         if (r4k_clock_unstable)
  76                 return;
  77
  78         r4k_clock_unstable = true;
  79
  80         pr_info("R4K timer is unstable due to %s\n", reason);
  81
  82         clocksource_mark_unstable(&clocksource_mips);
  83 }
  84
  85 static int r4k_cpufreq_callback(struct notifier_block *nb,
  86                                 unsigned long val, void *data)
  87 {
  88         if (val == CPUFREQ_POSTCHANGE)
  89                 r4k_clocksource_unstable("CPU frequency change");
  90
  91         return 0;
  92 }
  93
  94 static struct notifier_block r4k_cpufreq_notifier = {
  95         .notifier_call  = r4k_cpufreq_callback,
  96 };
  97
  98 static int __init r4k_register_cpufreq_notifier(void)
  99 {
 100         return cpufreq_register_notifier(&r4k_cpufreq_notifier,
 101                                          CPUFREQ_TRANSITION_NOTIFIER);
 102
 103 }
 104 core_initcall(r4k_register_cpufreq_notifier);
 105
 106 #endif /* !CONFIG_CPU_FREQ */
 107
 108 int __init init_r4k_clocksource(void)
 109 {
 110         if (!cpu_has_counter || !mips_hpt_frequency)
 111                 return -ENXIO;
 112
 113         /* Calculate a somewhat reasonable rating value */
 114         clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000;
 115
 116         /*
 117          * R2 onwards makes the count accessible to user mode so it can be used
 118          * by the VDSO (HWREna is configured by configure_hwrena()).
 119          */
 120         if (cpu_has_mips_r2_r6 && rdhwr_count_usable())
 121                 clocksource_mips.vdso_clock_mode = VDSO_CLOCKMODE_R4K;
 122
 123         clocksource_register_hz(&clocksource_mips, mips_hpt_frequency);
 124
 125 #ifndef CONFIG_CPU_FREQ
 126         sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency);
 127 #endif
 128
 129         return 0;
 130 }