timekeeping: Provide ktime_mono_to_any()

ktime based conversion function to map a monotonic time stamp to a
different CLOCK.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

include/linux/timekeeping.h

@@ -109,6 +109,7 @@ enum tk_offsets {
 extern ktime_t ktime_get(void);
 extern ktime_t ktime_get_with_offset(enum tk_offsets offs);
 extern ktime_t ktime_get_monotonic_offset(void);
+extern ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs);
 
 /**
  * ktime_get_real - get the real (wall-) time in ktime_t format
@@ -137,6 +138,14 @@ static inline ktime_t ktime_get_clocktai(void)
 	return ktime_get_with_offset(TK_OFFS_TAI);
 }
 
+/**
+ * ktime_mono_to_real - Convert monotonic time to clock realtime
+ */
+static inline ktime_t ktime_mono_to_real(ktime_t mono)
+{
+	return ktime_mono_to_any(mono, TK_OFFS_REAL);
+}
+
 /*
  * RTC specific
  */

kernel/time/timekeeping.c

@@ -450,6 +450,26 @@ ktime_t ktime_get_with_offset(enum tk_offsets offs)
 }
 EXPORT_SYMBOL_GPL(ktime_get_with_offset);
 
+/**
+ * ktime_mono_to_any() - convert mononotic time to any other time
+ * @tmono:	time to convert.
+ * @offs:	which offset to use
+ */
+ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs)
+{
+	ktime_t *offset = offsets[offs];
+	unsigned long seq;
+	ktime_t tconv;
+
+	do {
+		seq = read_seqcount_begin(&tk_core.seq);
+		tconv = ktime_add(tmono, *offset);
+	} while (read_seqcount_retry(&tk_core.seq, seq));
+
+	return tconv;
+}
+EXPORT_SYMBOL_GPL(ktime_mono_to_any);
+
 /**
  * ktime_get_ts64 - get the monotonic clock in timespec64 format
  * @ts:		pointer to timespec variable