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 */ 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 !clockevent_state_periodic(&i8253_clockevent)) 38 return 0; 39 40 return clocksource_i8253_init(); 41 } 42 arch_initcall(init_pit_clocksource); 43 #endif /* !CONFIG_X86_64 */ 44