time: move the timecounter/cyclecounter code into its own file.

The timecounter code has almost nothing to do with the clocksource
code. Let it live in its own file. This will help isolate the
timecounter users from the clocksource users in the source tree.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 122 insertions, 0 deletions

diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h
new file mode 100644
index 000000000000..146f07a6651b
--- /dev/null
+++ b/include/linux/timecounter.h
@@ -0,0 +1,122 @@
+/*
+ * 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>
+
+/**
+ * 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 CLOCKSOURCE_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
+ */
+struct timecounter {
+        const struct cyclecounter *cc;
+        cycle_t cycle_last;
+        u64 nsec;
+};
+
+/**
+ * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
+ * @cc:         Pointer to cycle counter.
+ * @cycles:     Cycles
+ *
+ * XXX - This could use some mult_lxl_ll() asm optimization. Same code
+ * as in cyc2ns, but with unsigned result.
+ */
+static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
+                                      cycle_t cycles)
+{
+        u64 ret = (u64)cycles;
+        ret = (ret * cc->mult) >> cc->shift;
+        return ret;
+}
+
+/**
+ * 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