1 files changed, 139 insertions, 0 deletions
diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h
new file mode 100644
index 000000000..4382035a7
--- /dev/null
+++ b/include/linux/timecounter.h
@@ -0,0 +1,139 @@
+/*
+ * linux/include/linux/timecounter.h
+ *
+ * based on code that migrated away from
+ * linux/include/linux/clocksource.h
+ *
+ * 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.
+ */
+#ifndef _LINUX_TIMECOUNTER_H
+#define _LINUX_TIMECOUNTER_H
+
+#include <linux/types.h>
+
+/* simplify initialization of mask field */
+#define CYCLECOUNTER_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
+
+/**
+ * struct cyclecounter - hardware abstraction for a free running counter
+ *	Provides completely state-free accessors to the underlying hardware.
+ *	Depending on which hardware it reads, the cycle counter may wrap
+ *	around quickly. Locking rules (if necessary) have to be defined
+ *	by the implementor and user of specific instances of this API.
+ *
+ * @read:		returns the current cycle value
+ * @mask:		bitmask for two's complement
+ *			subtraction of non 64 bit counters,
+ *			see CYCLECOUNTER_MASK() helper macro
+ * @mult:		cycle to nanosecond multiplier
+ * @shift:		cycle to nanosecond divisor (power of two)
+ */
+struct cyclecounter {
+	cycle_t (*read)(const struct cyclecounter *cc);
+	cycle_t mask;
+	u32 mult;
+	u32 shift;
+};
+
+/**
+ * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
+ *	Contains the state needed by timecounter_read() to detect
+ *	cycle counter wrap around. Initialize with
+ *	timecounter_init(). Also used to convert cycle counts into the
+ *	corresponding nanosecond counts with timecounter_cyc2time(). Users
+ *	of this code are responsible for initializing the underlying
+ *	cycle counter hardware, locking issues and reading the time
+ *	more often than the cycle counter wraps around. The nanosecond
+ *	counter will only wrap around after ~585 years.
+ *
+ * @cc:			the cycle counter used by this instance
+ * @cycle_last:		most recent cycle counter value seen by
+ *			timecounter_read()
+ * @nsec:		continuously increasing count
+ * @mask:		bit mask for maintaining the 'frac' field
+ * @frac:		accumulated fractional nanoseconds
+ */
+struct timecounter {
+	const struct cyclecounter *cc;
+	cycle_t cycle_last;
+	u64 nsec;
+	u64 mask;
+	u64 frac;
+};
+
+/**
+ * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
+ * @cc:		Pointer to cycle counter.
+ * @cycles:	Cycles
+ * @mask:	bit mask for maintaining the 'frac' field
+ * @frac:	pointer to storage for the fractional nanoseconds.
+ */
+static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
+				      cycle_t cycles, u64 mask, u64 *frac)
+{
+	u64 ns = (u64) cycles;
+
+	ns = (ns * cc->mult) + *frac;
+	*frac = ns & mask;
+	return ns >> cc->shift;
+}
+
+/**
+ * timecounter_adjtime - Shifts the time of the clock.
+ * @delta:	Desired change in nanoseconds.
+ */
+static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
+{
+	tc->nsec += delta;
+}
+
+/**
+ * timecounter_init - initialize a time counter
+ * @tc:			Pointer to time counter which is to be initialized/reset
+ * @cc:			A cycle counter, ready to be used.
+ * @start_tstamp:	Arbitrary initial time stamp.
+ *
+ * After this call the current cycle register (roughly) corresponds to
+ * the initial time stamp. Every call to timecounter_read() increments
+ * the time stamp counter by the number of elapsed nanoseconds.
+ */
+extern void timecounter_init(struct timecounter *tc,
+			     const struct cyclecounter *cc,
+			     u64 start_tstamp);
+
+/**
+ * timecounter_read - return nanoseconds elapsed since timecounter_init()
+ *                    plus the initial time stamp
+ * @tc:          Pointer to time counter.
+ *
+ * In other words, keeps track of time since the same epoch as
+ * the function which generated the initial time stamp.
+ */
+extern u64 timecounter_read(struct timecounter *tc);
+
+/**
+ * timecounter_cyc2time - convert a cycle counter to same
+ *                        time base as values returned by
+ *                        timecounter_read()
+ * @tc:		Pointer to time counter.
+ * @cycle_tstamp:	a value returned by tc->cc->read()
+ *
+ * Cycle counts that are converted correctly as long as they
+ * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
+ * with "max cycle count" == cs->mask+1.
+ *
+ * This allows conversion of cycle counter values which were generated
+ * in the past.
+ */
+extern u64 timecounter_cyc2time(struct timecounter *tc,
+				cycle_t cycle_tstamp);
+
+#endif