LXR linux/arch/x86/kernel/i8253.c

   1/*
   2 * 8253/PIT functions
   3 *
   4 */
   5#include <linux/clockchips.h>
   6#include <linux/init.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 */
  18struct clock_event_device *global_clock_event;
  19
  20void __init setup_pit_timer(void)
  21{
  22        clockevent_i8253_init(true);
  23        global_clock_event = &i8253_clockevent;
  24}
  25
  26#ifndef CONFIG_X86_64
  27static 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            !clockevent_state_periodic(&i8253_clockevent))
  38                return 0;
  39
  40        return clocksource_i8253_init();
  41}
  42arch_initcall(init_pit_clocksource);
  43#endif /* !CONFIG_X86_64 */
  44