[PATCH 4.4 01/21] time: Add cycles to nanoseconds translation

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christopher S. Hall <christopher.s.hall@xxxxxxxxx>

commit 6bd58f09e1d8cc6c50a824c00bf0d617919986a1 upstream.

The timekeeping code does not currently provide a way to translate
externally provided clocksource cycles to system time. The cycle count
is always provided by the result clocksource read() method internal to
the timekeeping code. The added function timekeeping_cycles_to_ns()
calculated a nanosecond value from a cycle count that can be added to
tk_read_base.base value yielding the current system time. This allows
clocksource cycle values external to the timekeeping code to provide a
cycle count that can be transformed to system time.

Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: kevin.b.stanton@xxxxxxxxx
Cc: kevin.j.clarke@xxxxxxxxx
Cc: hpa@xxxxxxxxx
Cc: jeffrey.t.kirsher@xxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Christopher S. Hall <christopher.s.hall@xxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/time/timekeeping.c |   25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -298,17 +298,34 @@ u32 (*arch_gettimeoffset)(void) = defaul
 static inline u32 arch_gettimeoffset(void) { return 0; }
 #endif
 
+static inline s64 timekeeping_delta_to_ns(struct tk_read_base *tkr,
+					  cycle_t delta)
+{
+	s64 nsec;
+
+	nsec = delta * tkr->mult + tkr->xtime_nsec;
+	nsec >>= tkr->shift;
+
+	/* If arch requires, add in get_arch_timeoffset() */
+	return nsec + arch_gettimeoffset();
+}
+
 static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
 {
 	cycle_t delta;
-	s64 nsec;
 
 	delta = timekeeping_get_delta(tkr);
+	return timekeeping_delta_to_ns(tkr, delta);
+}
 
-	nsec = (delta * tkr->mult + tkr->xtime_nsec) >> tkr->shift;
+static inline s64 timekeeping_cycles_to_ns(struct tk_read_base *tkr,
+					    cycle_t cycles)
+{
+	cycle_t delta;
 
-	/* If arch requires, add in get_arch_timeoffset() */
-	return nsec + arch_gettimeoffset();
+	/* calculate the delta since the last update_wall_time */
+	delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
+	return timekeeping_delta_to_ns(tkr, delta);
 }
 
 /**