arch/x86/kernel/i8253.c

   1 /*
   2  * 8253/PIT functions
   3  *
   4  */
   5 #include <linux/clockchips.h>
   6 #include <linux/module.h>
   7 #include <linux/timex.h>
   8 #include <linux/i8253.h>
   9
  10 #include <asm/hpet.h>
  11 #include <asm/time.h>
  12 #include <asm/smp.h>
  13
  14 /*
  15  * HPET replaces the PIT, when enabled. So we need to know, which of
  16  * the two timers is used
  17  */
  18 struct clock_event_device *global_clock_event;
  19
  20 void __init setup_pit_timer(void)
  21 {
  22         clockevent_i8253_init(true);
  23         global_clock_event = &i8253_clockevent;
  24 }
  25
  26 #ifndef CONFIG_X86_64
  27 static int __init init_pit_clocksource(void)
  28 {
  29          /*
  30           * Several reasons not to register PIT as a clocksource:
  31           *
  32           * - On SMP PIT does not scale due to i8253_lock
  33           * - when HPET is enabled
  34           * - when local APIC timer is active (PIT is switched off)
  35           */
  36         if (num_possible_cpus() > 1 || is_hpet_enabled() ||
  37             i8253_clockevent.mode != CLOCK_EVT_MODE_PERIODIC)
  38                 return 0;
  39
  40         return clocksource_i8253_init();
  41 }
  42 arch_initcall(init_pit_clocksource);
  43 #endif /* !CONFIG_X86_64 */