5 #include <linux/clockchips.h>
6 #include <linux/interrupt.h>
7 #include <linux/spinlock.h>
8 #include <linux/jiffies.h>
9 #include <linux/module.h>
10 #include <linux/timex.h>
11 #include <linux/delay.h>
12 #include <linux/init.h>
15 #include <asm/i8253.h>
19 DEFINE_RAW_SPINLOCK(i8253_lock);
20 EXPORT_SYMBOL(i8253_lock);
23 * HPET replaces the PIT, when enabled. So we need to know, which of
24 * the two timers is used
26 struct clock_event_device *global_clock_event;
29 * Initialize the PIT timer.
31 * This is also called after resume to bring the PIT into operation again.
33 static void init_pit_timer(enum clock_event_mode mode,
34 struct clock_event_device *evt)
36 raw_spin_lock(&i8253_lock);
39 case CLOCK_EVT_MODE_PERIODIC:
40 /* binary, mode 2, LSB/MSB, ch 0 */
41 outb_pit(0x34, PIT_MODE);
42 outb_pit(LATCH & 0xff , PIT_CH0); /* LSB */
43 outb_pit(LATCH >> 8 , PIT_CH0); /* MSB */
46 case CLOCK_EVT_MODE_SHUTDOWN:
47 case CLOCK_EVT_MODE_UNUSED:
48 if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
49 evt->mode == CLOCK_EVT_MODE_ONESHOT) {
50 outb_pit(0x30, PIT_MODE);
56 case CLOCK_EVT_MODE_ONESHOT:
58 outb_pit(0x38, PIT_MODE);
61 case CLOCK_EVT_MODE_RESUME:
62 /* Nothing to do here */
65 raw_spin_unlock(&i8253_lock);
69 * Program the next event in oneshot mode
71 * Delta is given in PIT ticks
73 static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
75 raw_spin_lock(&i8253_lock);
76 outb_pit(delta & 0xff , PIT_CH0); /* LSB */
77 outb_pit(delta >> 8 , PIT_CH0); /* MSB */
78 raw_spin_unlock(&i8253_lock);
84 * On UP the PIT can serve all of the possible timer functions. On SMP systems
85 * it can be solely used for the global tick.
87 * The profiling and update capabilities are switched off once the local apic is
88 * registered. This mechanism replaces the previous #ifdef LOCAL_APIC -
89 * !using_apic_timer decisions in do_timer_interrupt_hook()
91 static struct clock_event_device pit_ce = {
93 .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
94 .set_mode = init_pit_timer,
95 .set_next_event = pit_next_event,
101 * Initialize the conversion factor and the min/max deltas of the clock event
102 * structure and register the clock event source with the framework.
104 void __init setup_pit_timer(void)
107 * Start pit with the boot cpu mask and make it global after the
108 * IO_APIC has been initialized.
110 pit_ce.cpumask = cpumask_of(smp_processor_id());
111 pit_ce.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, pit_ce.shift);
112 pit_ce.max_delta_ns = clockevent_delta2ns(0x7FFF, &pit_ce);
113 pit_ce.min_delta_ns = clockevent_delta2ns(0xF, &pit_ce);
115 clockevents_register_device(&pit_ce);
116 global_clock_event = &pit_ce;
119 #ifndef CONFIG_X86_64
120 static int __init init_pit_clocksource(void)
123 * Several reasons not to register PIT as a clocksource:
125 * - On SMP PIT does not scale due to i8253_lock
126 * - when HPET is enabled
127 * - when local APIC timer is active (PIT is switched off)
129 if (num_possible_cpus() > 1 || is_hpet_enabled() ||
130 pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)
133 return clocksource_i8253_init();
135 arch_initcall(init_pit_clocksource);
136 #endif /* !CONFIG_X86_64 */