kernel/drivers/clocksource/dummy_timer.c

   1 /*
   2  *  linux/drivers/clocksource/dummy_timer.c
   3  *
   4  *  Copyright (C) 2013 ARM Ltd.
   5  *  All Rights Reserved
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11 #include <linux/clockchips.h>
  12 #include <linux/cpu.h>
  13 #include <linux/init.h>
  14 #include <linux/percpu.h>
  15 #include <linux/cpumask.h>
  16
  17 static DEFINE_PER_CPU(struct clock_event_device, dummy_timer_evt);
  18
  19 static void dummy_timer_setup(void)
  20 {
  21         int cpu = smp_processor_id();
  22         struct clock_event_device *evt = raw_cpu_ptr(&dummy_timer_evt);
  23
  24         evt->name       = "dummy_timer";
  25         evt->features   = CLOCK_EVT_FEAT_PERIODIC |
  26                           CLOCK_EVT_FEAT_ONESHOT |
  27                           CLOCK_EVT_FEAT_DUMMY;
  28         evt->rating     = 100;
  29         evt->cpumask    = cpumask_of(cpu);
  30
  31         clockevents_register_device(evt);
  32 }
  33
  34 static int dummy_timer_cpu_notify(struct notifier_block *self,
  35                                       unsigned long action, void *hcpu)
  36 {
  37         if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
  38                 dummy_timer_setup();
  39
  40         return NOTIFY_OK;
  41 }
  42
  43 static struct notifier_block dummy_timer_cpu_nb = {
  44         .notifier_call = dummy_timer_cpu_notify,
  45 };
  46
  47 static int __init dummy_timer_register(void)
  48 {
  49         int err = 0;
  50
  51         cpu_notifier_register_begin();
  52         err = __register_cpu_notifier(&dummy_timer_cpu_nb);
  53         if (err)
  54                 goto out;
  55
  56         /* We won't get a call on the boot CPU, so register immediately */
  57         if (num_possible_cpus() > 1)
  58                 dummy_timer_setup();
  59
  60 out:
  61         cpu_notifier_register_done();
  62         return err;
  63 }
  64 early_initcall(dummy_timer_register);