1 files changed, 76 insertions, 0 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index ca89e1593f08..c46c931a7fe7 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -31,6 +31,82 @@
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
 #include <linux/tick.h>
 
+void timecounter_init(struct timecounter *tc,
+                      const struct cyclecounter *cc,
+                      u64 start_tstamp)
+{
+        tc->cc = cc;
+        tc->cycle_last = cc->read(cc);
+        tc->nsec = start_tstamp;
+}
+EXPORT_SYMBOL(timecounter_init);
+
+/**
+ * timecounter_read_delta - get nanoseconds since last call of this function
+ * @tc:         Pointer to time counter
+ *
+ * When the underlying cycle counter runs over, this will be handled
+ * correctly as long as it does not run over more than once between
+ * calls.
+ *
+ * The first call to this function for a new time counter initializes
+ * the time tracking and returns an undefined result.
+ */
+static u64 timecounter_read_delta(struct timecounter *tc)
+{
+        cycle_t cycle_now, cycle_delta;
+        u64 ns_offset;
+
+        /* read cycle counter: */
+        cycle_now = tc->cc->read(tc->cc);
+
+        /* calculate the delta since the last timecounter_read_delta(): */
+        cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
+
+        /* convert to nanoseconds: */
+        ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
+
+        /* update time stamp of timecounter_read_delta() call: */
+        tc->cycle_last = cycle_now;
+
+        return ns_offset;
+}
+
+u64 timecounter_read(struct timecounter *tc)
+{
+        u64 nsec;
+
+        /* increment time by nanoseconds since last call */
+        nsec = timecounter_read_delta(tc);
+        nsec += tc->nsec;
+        tc->nsec = nsec;
+
+        return nsec;
+}
+EXPORT_SYMBOL(timecounter_read);
+
+u64 timecounter_cyc2time(struct timecounter *tc,
+                         cycle_t cycle_tstamp)
+{
+        u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
+        u64 nsec;
+
+        /*
+         * Instead of always treating cycle_tstamp as more recent
+         * than tc->cycle_last, detect when it is too far in the
+         * future and treat it as old time stamp instead.
+         */
+        if (cycle_delta > tc->cc->mask / 2) {
+                cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
+                nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
+        } else {
+                nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
+        }
+
+        return nsec;
+}
+EXPORT_SYMBOL(timecounter_cyc2time);
+
 /* XXX - Would like a better way for initializing curr_clocksource */
 extern struct clocksource clocksource_jiffies;