--- /dev/null
+/*
+ * i8253 PIT clocksource
+ */
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/spinlock.h>
+#include <linux/timex.h>
+#include <linux/module.h>
+#include <linux/i8253.h>
+#include <linux/smp.h>
+
+/*
+ * Protects access to I/O ports
+ *
+ * 0040-0043 : timer0, i8253 / i8254
+ * 0061-0061 : NMI Control Register which contains two speaker control bits.
+ */
+DEFINE_RAW_SPINLOCK(i8253_lock);
+EXPORT_SYMBOL(i8253_lock);
+
+#ifdef CONFIG_CLKSRC_I8253
+/*
+ * Since the PIT overflows every tick, its not very useful
+ * to just read by itself. So use jiffies to emulate a free
+ * running counter:
+ */
+static cycle_t i8253_read(struct clocksource *cs)
+{
+ static int old_count;
+ static u32 old_jifs;
+ unsigned long flags;
+ int count;
+ u32 jifs;
+
+ raw_spin_lock_irqsave(&i8253_lock, flags);
+ /*
+ * Although our caller may have the read side of jiffies_lock,
+ * this is now a seqlock, and we are cheating in this routine
+ * by having side effects on state that we cannot undo if
+ * there is a collision on the seqlock and our caller has to
+ * retry. (Namely, old_jifs and old_count.) So we must treat
+ * jiffies as volatile despite the lock. We read jiffies
+ * before latching the timer count to guarantee that although
+ * the jiffies value might be older than the count (that is,
+ * the counter may underflow between the last point where
+ * jiffies was incremented and the point where we latch the
+ * count), it cannot be newer.
+ */
+ jifs = jiffies;
+ outb_p(0x00, PIT_MODE); /* latch the count ASAP */
+ count = inb_p(PIT_CH0); /* read the latched count */
+ count |= inb_p(PIT_CH0) << 8;
+
+ /* VIA686a test code... reset the latch if count > max + 1 */
+ if (count > PIT_LATCH) {
+ outb_p(0x34, PIT_MODE);
+ outb_p(PIT_LATCH & 0xff, PIT_CH0);
+ outb_p(PIT_LATCH >> 8, PIT_CH0);
+ count = PIT_LATCH - 1;
+ }
+
+ /*
+ * It's possible for count to appear to go the wrong way for a
+ * couple of reasons:
+ *
+ * 1. The timer counter underflows, but we haven't handled the
+ * resulting interrupt and incremented jiffies yet.
+ * 2. Hardware problem with the timer, not giving us continuous time,
+ * the counter does small "jumps" upwards on some Pentium systems,
+ * (see c't 95/10 page 335 for Neptun bug.)
+ *
+ * Previous attempts to handle these cases intelligently were
+ * buggy, so we just do the simple thing now.
+ */
+ if (count > old_count && jifs == old_jifs)
+ count = old_count;
+
+ old_count = count;
+ old_jifs = jifs;
+
+ raw_spin_unlock_irqrestore(&i8253_lock, flags);
+
+ count = (PIT_LATCH - 1) - count;
+
+ return (cycle_t)(jifs * PIT_LATCH) + count;
+}
+
+static struct clocksource i8253_cs = {
+ .name = "pit",
+ .rating = 110,
+ .read = i8253_read,
+ .mask = CLOCKSOURCE_MASK(32),
+};
+
+int __init clocksource_i8253_init(void)
+{
+ return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
+}
+#endif
+
+#ifdef CONFIG_CLKEVT_I8253
+/*
+ * 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_p(0x34, PIT_MODE);
+ outb_p(PIT_LATCH & 0xff , PIT_CH0); /* LSB */
+ outb_p(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_p(0x30, PIT_MODE);
+ outb_p(0, PIT_CH0);
+ outb_p(0, PIT_CH0);
+ }
+ break;
+
+ case CLOCK_EVT_MODE_ONESHOT:
+ /* One shot setup */
+ outb_p(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_p(delta & 0xff , PIT_CH0); /* LSB */
+ outb_p(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.
+ */
+struct clock_event_device i8253_clockevent = {
+ .name = "pit",
+ .features = CLOCK_EVT_FEAT_PERIODIC,
+ .set_mode = init_pit_timer,
+ .set_next_event = pit_next_event,
+};
+
+/*
+ * 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 clockevent_i8253_init(bool oneshot)
+{
+ if (oneshot)
+ i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
+ /*
+ * Start pit with the boot cpu mask. x86 might make it global
+ * when it is used as broadcast device later.
+ */
+ i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
+
+ clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
+ 0xF, 0x7FFF);
+}
+#endif
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