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_set_mode(enum clock_event_mode mode,
  20                            struct clock_event_device *evt)
  21 {
  22         /*
  23          * Core clockevents code will call this when exchanging timer devices.
  24          * We don't need to do anything here.
  25          */
  26 }
  27
  28 static void dummy_timer_setup(void)
  29 {
  30         int cpu = smp_processor_id();
  31         struct clock_event_device *evt = __this_cpu_ptr(&dummy_timer_evt);
  32
  33         evt->name       = "dummy_timer";
  34         evt->features   = CLOCK_EVT_FEAT_PERIODIC |
  35                           CLOCK_EVT_FEAT_ONESHOT |
  36                           CLOCK_EVT_FEAT_DUMMY;
  37         evt->rating     = 100;
  38         evt->set_mode   = dummy_timer_set_mode;
  39         evt->cpumask    = cpumask_of(cpu);
  40
  41         clockevents_register_device(evt);
  42 }
  43
  44 static int dummy_timer_cpu_notify(struct notifier_block *self,
  45                                       unsigned long action, void *hcpu)
  46 {
  47         if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
  48                 dummy_timer_setup();
  49
  50         return NOTIFY_OK;
  51 }
  52
  53 static struct notifier_block dummy_timer_cpu_nb = {
  54         .notifier_call = dummy_timer_cpu_notify,
  55 };
  56
  57 static int __init dummy_timer_register(void)
  58 {
  59         int err = 0;
  60
  61         cpu_notifier_register_begin();
  62         err = __register_cpu_notifier(&dummy_timer_cpu_nb);
  63         if (err)
  64                 goto out;
  65
  66         /* We won't get a call on the boot CPU, so register immediately */
  67         if (num_possible_cpus() > 1)
  68                 dummy_timer_setup();
  69
  70 out:
  71         cpu_notifier_register_done();
  72         return err;
  73 }
  74 early_initcall(dummy_timer_register);