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/init.h>
  13 #include <linux/io.h>
  14
  15 #include <asm/i8253.h>
  16 #include <asm/hpet.h>
  17 #include <asm/smp.h>
  18
  19 DEFINE_RAW_SPINLOCK(i8253_lock);
  20 EXPORT_SYMBOL(i8253_lock);
  21
  22 /*
  23  * HPET replaces the PIT, when enabled. So we need to know, which of
  24  * the two timers is used
  25  */
  26 struct clock_event_device *global_clock_event;
  27
  28 /*
  29  * Initialize the PIT timer.
  30  *
  31  * This is also called after resume to bring the PIT into operation again.
  32  */
  33 static void init_pit_timer(enum clock_event_mode mode,
  34                            struct clock_event_device *evt)
  35 {
  36         raw_spin_lock(&i8253_lock);
  37
  38         switch (mode) {
  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 */
  44                 break;
  45
  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);
  51                         outb_pit(0, PIT_CH0);
  52                         outb_pit(0, PIT_CH0);
  53                 }
  54                 break;
  55
  56         case CLOCK_EVT_MODE_ONESHOT:
  57                 /* One shot setup */
  58                 outb_pit(0x38, PIT_MODE);
  59                 break;
  60
  61         case CLOCK_EVT_MODE_RESUME:
  62                 /* Nothing to do here */
  63                 break;
  64         }
  65         raw_spin_unlock(&i8253_lock);
  66 }
  67
  68 /*
  69  * Program the next event in oneshot mode
  70  *
  71  * Delta is given in PIT ticks
  72  */
  73 static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
  74 {
  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);
  79
  80         return 0;
  81 }
  82
  83 /*
  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.
  86  *
  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()
  90  */
  91 static struct clock_event_device pit_ce = {
  92         .name           = "pit",
  93         .features       = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
  94         .set_mode       = init_pit_timer,
  95         .set_next_event = pit_next_event,
  96         .irq            = 0,
  97 };
  98
  99 /*
 100  * Initialize the conversion factor and the min/max deltas of the clock event
 101  * structure and register the clock event source with the framework.
 102  */
 103 void __init setup_pit_timer(void)
 104 {
 105         /*
 106          * Start pit with the boot cpu mask and make it global after the
 107          * IO_APIC has been initialized.
 108          */
 109         pit_ce.cpumask = cpumask_of(smp_processor_id());
 110
 111         clockevents_config_and_register(&pit_ce, CLOCK_TICK_RATE, 0xF, 0x7FFF);
 112         global_clock_event = &pit_ce;
 113 }
 114
 115 #ifndef CONFIG_X86_64
 116 static int __init init_pit_clocksource(void)
 117 {
 118          /*
 119           * Several reasons not to register PIT as a clocksource:
 120           *
 121           * - On SMP PIT does not scale due to i8253_lock
 122           * - when HPET is enabled
 123           * - when local APIC timer is active (PIT is switched off)
 124           */
 125         if (num_possible_cpus() > 1 || is_hpet_enabled() ||
 126             pit_ce.mode != CLOCK_EVT_MODE_PERIODIC)
 127                 return 0;
 128
 129         return clocksource_i8253_init();
 130 }
 131 arch_initcall(init_pit_clocksource);
 132 #endif /* !CONFIG_X86_64 */