Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / kernel / time / timecounter.c

diff --git a/kernel/kernel/time/timecounter.c b/kernel/kernel/time/timecounter.c
new file mode 100644 (file)
index 0000000..4687b31
--- /dev/null
+++ b/kernel/kernel/time/timecounter.c
@@ -0,0 +1,112 @@
+/*
+ * linux/kernel/time/timecounter.c
+ *
+ * based on code that migrated away from
+ * linux/kernel/time/clocksource.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/export.h>
+#include <linux/timecounter.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;
+       tc->mask = (1ULL << cc->shift) - 1;
+       tc->frac = 0;
+}
+EXPORT_SYMBOL_GPL(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,
+                                       tc->mask, &tc->frac);
+
+       /* 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_GPL(timecounter_read);
+
+/*
+ * This is like cyclecounter_cyc2ns(), but it is used for computing a
+ * time previous to the time stored in the cycle counter.
+ */
+static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
+                              cycle_t cycles, u64 mask, u64 frac)
+{
+       u64 ns = (u64) cycles;
+
+       ns = ((ns * cc->mult) - frac) >> cc->shift;
+
+       return ns;
+}
+
+u64 timecounter_cyc2time(struct timecounter *tc,
+                        cycle_t cycle_tstamp)
+{
+       u64 delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
+       u64 nsec = tc->nsec, frac = tc->frac;
+
+       /*
+        * 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 (delta > tc->cc->mask / 2) {
+               delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
+               nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
+       } else {
+               nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
+       }
+
+       return nsec;
+}
+EXPORT_SYMBOL_GPL(timecounter_cyc2time);