arch/x86/kernel/i8253.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * 8253/PIT functions
   4  *
   5  */
   6 #include <linux/clockchips.h>
   7 #include <linux/init.h>
   8 #include <linux/timex.h>
   9 #include <linux/i8253.h>
  10
  11 #include <asm/hpet.h>
  12 #include <asm/time.h>
  13 #include <asm/smp.h>
  14
  15 /*
  16  * HPET replaces the PIT, when enabled. So we need to know, which of
  17  * the two timers is used
  18  */
  19 struct clock_event_device *global_clock_event;
  20
  21 void __init setup_pit_timer(void)
  22 {
  23         clockevent_i8253_init(true);
  24         global_clock_event = &i8253_clockevent;
  25 }
  26
  27 #ifndef CONFIG_X86_64
  28 static int __init init_pit_clocksource(void)
  29 {
  30          /*
  31           * Several reasons not to register PIT as a clocksource:
  32           *
  33           * - On SMP PIT does not scale due to i8253_lock
  34           * - when HPET is enabled
  35           * - when local APIC timer is active (PIT is switched off)
  36           */
  37         if (num_possible_cpus() > 1 || is_hpet_enabled() ||
  38             !clockevent_state_periodic(&i8253_clockevent))
  39                 return 0;
  40
  41         return clocksource_i8253_init();
  42 }
  43 arch_initcall(init_pit_clocksource);
  44 #endif /* !CONFIG_X86_64 */