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 
setup_pit_timer(void)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
init_pit_clocksource(void)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 */
44