arch/x86/kernel/i8253.c

   1 /*
   2  * 8253/PIT functions
   3  *
   4  */
   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/i8253.h>
  13 #include <linux/init.h>
  14 #include <linux/io.h>
  15
  16 #include <asm/hpet.h>
  17 #include <asm/smp.h>
  18
  19 /*
  20  * HPET replaces the PIT, when enabled. So we need to know, which of
  21  * the two timers is used
  22  */
  23 struct clock_event_device *global_clock_event;
  24
  25 /*
  26  * Initialize the PIT timer.
  27  *
  28  * This is also called after resume to bring the PIT into operation again.
  29  */
  30 static void init_pit_timer(enum clock_event_mode mode,
  31                            struct clock_event_device *evt)
  32 {
  33         raw_spin_lock(&i8253_lock);
  34
  35         switch (mode) {
  36         case CLOCK_EVT_MODE_PERIODIC:
  37                 /* binary, mode 2, LSB/MSB, ch 0 */
  38                 outb_pit(0x34, PIT_MODE);
  39                 outb_pit(LATCH & 0xff , PIT_CH0);       /* LSB */
  40                 outb_pit(LATCH >> 8 , PIT_CH0);         /* MSB */
  41                 break;
  42
  43         case CLOCK_EVT_MODE_SHUTDOWN:
  44         case CLOCK_EVT_MODE_UNUSED:
  45                 if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
  46                     evt->mode == CLOCK_EVT_MODE_ONESHOT) {
  47                         outb_pit(0x30, PIT_MODE);
  48                         outb_pit(0, PIT_CH0);
  49                         outb_pit(0, PIT_CH0);
  50                 }
  51                 break;
  52
  53         case CLOCK_EVT_MODE_ONESHOT:
  54                 /* One shot setup */
  55                 outb_pit(0x38, PIT_MODE);
  56                 break;
  57
  58         case CLOCK_EVT_MODE_RESUME:
  59                 /* Nothing to do here */
  60                 break;
  61         }
  62         raw_spin_unlock(&i8253_lock);
  63 }
  64
  65 /*
  66  * Program the next event in oneshot mode
  67  *
  68  * Delta is given in PIT ticks
  69  */
  70 static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
  71 {
  72         raw_spin_lock(&i8253_lock);
  73         outb_pit(delta & 0xff , PIT_CH0);       /* LSB */
  74         outb_pit(delta >> 8 , PIT_CH0);         /* MSB */
  75         raw_spin_unlock(&i8253_lock);
  76
  77         return 0;
  78 }
  79
  80 /*
  81  * On UP the PIT can serve all of the possible timer functions. On SMP systems
  82  * it can be solely used for the global tick.
  83  *
  84  * The profiling and update capabilities are switched off once the local apic is
  85  * registered. This mechanism replaces the previous #ifdef LOCAL_APIC -
  86  * !using_apic_timer decisions in do_timer_interrupt_hook()
  87  */
  88 static struct clock_event_device pit_ce = {
  89         .name           = "pit",
  90         .features       = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
  91         .set_mode       = init_pit_timer,
  92         .set_next_event = pit_next_event,
  93         .irq            = 0,
  94 };
  95
  96 /*
  97  * Initialize the conversion factor and the min/max deltas of the clock event
  98  * structure and register the clock event source with the framework.
  99  */
 100 void __init setup_pit_timer(void)
 101 {
 102         /*
 103          * Start pit with the boot cpu mask and make it global after the
 104          * IO_APIC has been initialized.
 105          */
 106         pit_ce.cpumask = cpumask_of(smp_processor_id());
 107
 108         clockevents_config_and_register(&pit_ce, CLOCK_TICK_RATE, 0xF, 0x7FFF);
 109         global_clock_event = &pit_ce;
 110 }
 111
 112 #ifndef CONFIG_X86_64
 113 static int __init init_pit_clocksource(void)
 114 {
 115          /*
 116           * Several reasons not to register PIT as a clocksource:
 117           *
 118           * - On SMP PIT does not scale due to i8253_lock
 119           * - when HPET is enabled
 120           * - when local APIC timer is active (PIT is switched off)
 121           */
 122         if (num_possible_cpus() > 1 || is_hpet_enabled() ||
 123             pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)
 124                 return 0;
 125
 126         return clocksource_i8253_init();
 127 }
 128 arch_initcall(init_pit_clocksource);
 129 #endif /* !CONFIG_X86_64 */