drivers/clocksource/i8253.c

   1 /*
   2  * i8253 PIT clocksource
   3  */
   4 #include <linux/clockchips.h>
   5 #include <linux/init.h>
   6 #include <linux/io.h>
   7 #include <linux/spinlock.h>
   8 #include <linux/timex.h>
   9 #include <linux/module.h>
  10 #include <linux/i8253.h>
  11 #include <linux/smp.h>
  12
  13 /*
  14  * Protects access to I/O ports
  15  *
  16  * 0040-0043 : timer0, i8253 / i8254
  17  * 0061-0061 : NMI Control Register which contains two speaker control bits.
  18  */
  19 DEFINE_RAW_SPINLOCK(i8253_lock);
  20 EXPORT_SYMBOL(i8253_lock);
  21
  22 #ifdef CONFIG_CLKSRC_I8253
  23 /*
  24  * Since the PIT overflows every tick, its not very useful
  25  * to just read by itself. So use jiffies to emulate a free
  26  * running counter:
  27  */
  28 static cycle_t i8253_read(struct clocksource *cs)
  29 {
  30         static int old_count;
  31         static u32 old_jifs;
  32         unsigned long flags;
  33         int count;
  34         u32 jifs;
  35
  36         raw_spin_lock_irqsave(&i8253_lock, flags);
  37         /*
  38          * Although our caller may have the read side of jiffies_lock,
  39          * this is now a seqlock, and we are cheating in this routine
  40          * by having side effects on state that we cannot undo if
  41          * there is a collision on the seqlock and our caller has to
  42          * retry.  (Namely, old_jifs and old_count.)  So we must treat
  43          * jiffies as volatile despite the lock.  We read jiffies
  44          * before latching the timer count to guarantee that although
  45          * the jiffies value might be older than the count (that is,
  46          * the counter may underflow between the last point where
  47          * jiffies was incremented and the point where we latch the
  48          * count), it cannot be newer.
  49          */
  50         jifs = jiffies;
  51         outb_p(0x00, PIT_MODE); /* latch the count ASAP */
  52         count = inb_p(PIT_CH0); /* read the latched count */
  53         count |= inb_p(PIT_CH0) << 8;
  54
  55         /* VIA686a test code... reset the latch if count > max + 1 */
  56         if (count > PIT_LATCH) {
  57                 outb_p(0x34, PIT_MODE);
  58                 outb_p(PIT_LATCH & 0xff, PIT_CH0);
  59                 outb_p(PIT_LATCH >> 8, PIT_CH0);
  60                 count = PIT_LATCH - 1;
  61         }
  62
  63         /*
  64          * It's possible for count to appear to go the wrong way for a
  65          * couple of reasons:
  66          *
  67          *  1. The timer counter underflows, but we haven't handled the
  68          *     resulting interrupt and incremented jiffies yet.
  69          *  2. Hardware problem with the timer, not giving us continuous time,
  70          *     the counter does small "jumps" upwards on some Pentium systems,
  71          *     (see c't 95/10 page 335 for Neptun bug.)
  72          *
  73          * Previous attempts to handle these cases intelligently were
  74          * buggy, so we just do the simple thing now.
  75          */
  76         if (count > old_count && jifs == old_jifs)
  77                 count = old_count;
  78
  79         old_count = count;
  80         old_jifs = jifs;
  81
  82         raw_spin_unlock_irqrestore(&i8253_lock, flags);
  83
  84         count = (PIT_LATCH - 1) - count;
  85
  86         return (cycle_t)(jifs * PIT_LATCH) + count;
  87 }
  88
  89 static struct clocksource i8253_cs = {
  90         .name           = "pit",
  91         .rating         = 110,
  92         .read           = i8253_read,
  93         .mask           = CLOCKSOURCE_MASK(32),
  94 };
  95
  96 int __init clocksource_i8253_init(void)
  97 {
  98         return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
  99 }
 100 #endif
 101
 102 #ifdef CONFIG_CLKEVT_I8253
 103 static int pit_shutdown(struct clock_event_device *evt)
 104 {
 105         if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
 106                 return 0;
 107
 108         raw_spin_lock(&i8253_lock);
 109
 110         outb_p(0x30, PIT_MODE);
 111         outb_p(0, PIT_CH0);
 112         outb_p(0, PIT_CH0);
 113
 114         raw_spin_unlock(&i8253_lock);
 115         return 0;
 116 }
 117
 118 static int pit_set_oneshot(struct clock_event_device *evt)
 119 {
 120         raw_spin_lock(&i8253_lock);
 121         outb_p(0x38, PIT_MODE);
 122         raw_spin_unlock(&i8253_lock);
 123         return 0;
 124 }
 125
 126 static int pit_set_periodic(struct clock_event_device *evt)
 127 {
 128         raw_spin_lock(&i8253_lock);
 129
 130         /* binary, mode 2, LSB/MSB, ch 0 */
 131         outb_p(0x34, PIT_MODE);
 132         outb_p(PIT_LATCH & 0xff, PIT_CH0);      /* LSB */
 133         outb_p(PIT_LATCH >> 8, PIT_CH0);        /* MSB */
 134
 135         raw_spin_unlock(&i8253_lock);
 136         return 0;
 137 }
 138
 139 /*
 140  * Program the next event in oneshot mode
 141  *
 142  * Delta is given in PIT ticks
 143  */
 144 static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
 145 {
 146         raw_spin_lock(&i8253_lock);
 147         outb_p(delta & 0xff , PIT_CH0); /* LSB */
 148         outb_p(delta >> 8 , PIT_CH0);           /* MSB */
 149         raw_spin_unlock(&i8253_lock);
 150
 151         return 0;
 152 }
 153
 154 /*
 155  * On UP the PIT can serve all of the possible timer functions. On SMP systems
 156  * it can be solely used for the global tick.
 157  */
 158 struct clock_event_device i8253_clockevent = {
 159         .name                   = "pit",
 160         .features               = CLOCK_EVT_FEAT_PERIODIC,
 161         .set_state_shutdown     = pit_shutdown,
 162         .set_state_periodic     = pit_set_periodic,
 163         .set_next_event         = pit_next_event,
 164 };
 165
 166 /*
 167  * Initialize the conversion factor and the min/max deltas of the clock event
 168  * structure and register the clock event source with the framework.
 169  */
 170 void __init clockevent_i8253_init(bool oneshot)
 171 {
 172         if (oneshot) {
 173                 i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
 174                 i8253_clockevent.set_state_oneshot = pit_set_oneshot;
 175         }
 176         /*
 177          * Start pit with the boot cpu mask. x86 might make it global
 178          * when it is used as broadcast device later.
 179          */
 180         i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
 181
 182         clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
 183                                         0xF, 0x7FFF);
 184 }
 185 #endif