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-rw-r--r--kernel/time/timecounter.c99
1 files changed, 99 insertions, 0 deletions
diff --git a/kernel/time/timecounter.c b/kernel/time/timecounter.c
new file mode 100644
index 000000000..e6285288d
--- /dev/null
+++ b/kernel/time/timecounter.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Based on clocksource code. See commit 74d23cc704d1
+ */
+#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)
+{
+ u64 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,
+ u64 cycles, u64 mask, u64 frac)
+{
+ u64 ns = (u64) cycles;
+
+ ns = ((ns * cc->mult) - frac) >> cc->shift;
+
+ return ns;
+}
+
+u64 timecounter_cyc2time(const struct timecounter *tc,
+ u64 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);