/* * 8253/PIT functions * */ #include #include #include #include #include #include #include #include #include #include #include #include /* * HPET replaces the PIT, when enabled. So we need to know, which of * the two timers is used */ struct clock_event_device *global_clock_event; /* * Initialize the PIT timer. * * This is also called after resume to bring the PIT into operation again. */ static void init_pit_timer(enum clock_event_mode mode, struct clock_event_device *evt) { raw_spin_lock(&i8253_lock); switch (mode) { case CLOCK_EVT_MODE_PERIODIC: /* binary, mode 2, LSB/MSB, ch 0 */ outb_pit(0x34, PIT_MODE); outb_pit(LATCH & 0xff , PIT_CH0); /* LSB */ outb_pit(LATCH >> 8 , PIT_CH0); /* MSB */ break; case CLOCK_EVT_MODE_SHUTDOWN: case CLOCK_EVT_MODE_UNUSED: if (evt->mode == CLOCK_EVT_MODE_PERIODIC || evt->mode == CLOCK_EVT_MODE_ONESHOT) { outb_pit(0x30, PIT_MODE); outb_pit(0, PIT_CH0); outb_pit(0, PIT_CH0); } break; case CLOCK_EVT_MODE_ONESHOT: /* One shot setup */ outb_pit(0x38, PIT_MODE); break; case CLOCK_EVT_MODE_RESUME: /* Nothing to do here */ break; } raw_spin_unlock(&i8253_lock); } /* * Program the next event in oneshot mode * * Delta is given in PIT ticks */ static int pit_next_event(unsigned long delta, struct clock_event_device *evt) { raw_spin_lock(&i8253_lock); outb_pit(delta & 0xff , PIT_CH0); /* LSB */ outb_pit(delta >> 8 , PIT_CH0); /* MSB */ raw_spin_unlock(&i8253_lock); return 0; } /* * On UP the PIT can serve all of the possible timer functions. On SMP systems * it can be solely used for the global tick. * * The profiling and update capabilities are switched off once the local apic is * registered. This mechanism replaces the previous #ifdef LOCAL_APIC - * !using_apic_timer decisions in do_timer_interrupt_hook() */ static struct clock_event_device pit_ce = { .name = "pit", .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, .set_mode = init_pit_timer, .set_next_event = pit_next_event, .irq = 0, }; /* * Initialize the conversion factor and the min/max deltas of the clock event * structure and register the clock event source with the framework. */ void __init setup_pit_timer(void) { /* * Start pit with the boot cpu mask and make it global after the * IO_APIC has been initialized. */ pit_ce.cpumask = cpumask_of(smp_processor_id()); clockevents_config_and_register(&pit_ce, CLOCK_TICK_RATE, 0xF, 0x7FFF); global_clock_event = &pit_ce; } #ifndef CONFIG_X86_64 static int __init init_pit_clocksource(void) { /* * Several reasons not to register PIT as a clocksource: * * - On SMP PIT does not scale due to i8253_lock * - when HPET is enabled * - when local APIC timer is active (PIT is switched off) */ if (num_possible_cpus() > 1 || is_hpet_enabled() || pit_ce.mode != CLOCK_EVT_MODE_PERIODIC) return 0; return clocksource_i8253_init(); } arch_initcall(init_pit_clocksource); #endif /* !CONFIG_X86_64 */