2 * i8253 PIT clocksource
4 #include <linux/clockchips.h>
5 #include <linux/init.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>
14 * Protects access to I/O ports
16 * 0040-0043 : timer0, i8253 / i8254
17 * 0061-0061 : NMI Control Register which contains two speaker control bits.
19 DEFINE_RAW_SPINLOCK(i8253_lock);
20 EXPORT_SYMBOL(i8253_lock);
22 #ifdef CONFIG_CLKSRC_I8253
24 * Since the PIT overflows every tick, its not very useful
25 * to just read by itself. So use jiffies to emulate a free
28 static cycle_t i8253_read(struct clocksource *cs)
36 raw_spin_lock_irqsave(&i8253_lock, flags);
38 * Although our caller may have the read side of xtime_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.
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;
55 /* VIA686a test code... reset the latch if count > max + 1 */
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;
64 * It's possible for count to appear to go the wrong way for a
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.)
73 * Previous attempts to handle these cases intelligently were
74 * buggy, so we just do the simple thing now.
76 if (count > old_count && jifs == old_jifs)
82 raw_spin_unlock_irqrestore(&i8253_lock, flags);
84 count = (PIT_LATCH - 1) - count;
86 return (cycle_t)(jifs * PIT_LATCH) + count;
89 static struct clocksource i8253_cs = {
93 .mask = CLOCKSOURCE_MASK(32),
96 int __init clocksource_i8253_init(void)
98 return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
102 #ifdef CONFIG_CLKEVT_I8253
104 * Initialize the PIT timer.
106 * This is also called after resume to bring the PIT into operation again.
108 static void init_pit_timer(enum clock_event_mode mode,
109 struct clock_event_device *evt)
111 raw_spin_lock(&i8253_lock);
114 case CLOCK_EVT_MODE_PERIODIC:
115 /* binary, mode 2, LSB/MSB, ch 0 */
116 outb_p(0x34, PIT_MODE);
117 outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
118 outb_p(LATCH >> 8 , PIT_CH0); /* MSB */
121 case CLOCK_EVT_MODE_SHUTDOWN:
122 case CLOCK_EVT_MODE_UNUSED:
123 if (evt->mode == CLOCK_EVT_MODE_PERIODIC ||
124 evt->mode == CLOCK_EVT_MODE_ONESHOT) {
125 outb_p(0x30, PIT_MODE);
131 case CLOCK_EVT_MODE_ONESHOT:
133 outb_p(0x38, PIT_MODE);
136 case CLOCK_EVT_MODE_RESUME:
137 /* Nothing to do here */
140 raw_spin_unlock(&i8253_lock);
144 * Program the next event in oneshot mode
146 * Delta is given in PIT ticks
148 static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
150 raw_spin_lock(&i8253_lock);
151 outb_p(delta & 0xff , PIT_CH0); /* LSB */
152 outb_p(delta >> 8 , PIT_CH0); /* MSB */
153 raw_spin_unlock(&i8253_lock);
159 * On UP the PIT can serve all of the possible timer functions. On SMP systems
160 * it can be solely used for the global tick.
162 struct clock_event_device i8253_clockevent = {
164 .features = CLOCK_EVT_FEAT_PERIODIC,
165 .set_mode = init_pit_timer,
166 .set_next_event = pit_next_event,
170 * Initialize the conversion factor and the min/max deltas of the clock event
171 * structure and register the clock event source with the framework.
173 void __init clockevent_i8253_init(bool oneshot)
176 i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
178 * Start pit with the boot cpu mask. x86 might make it global
179 * when it is used as broadcast device later.
181 i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
183 clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,