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 */ 45