[PATCH 1/4] time: add ktime_get_cycles64() api

[Mahesh Bandewar]

add a method to retrieve raw cycles in the same fashion as there are
ktime_get_* methods available for supported time-bases. The method
continues using the 'struct timespec64' since the UAPI uses 'struct
ptp_clock_time'.

The caller can perform operation equivalent of timespec64_to_ns() to
retrieve raw-cycles value. The precision loss because of this conversion
should be none for 64 bit cycle counters and nominal at 96 bit counters
(considering UAPI of s64 + u32 of 'struct ptp_clock_time).

Signed-off-by: Mahesh Bandewar <maheshb@xxxxxxxxxx>
CC: John Stultz <jstultz@xxxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Stephen Boyd <sboyd@xxxxxxxxxx>
CC: Richard Cochran <richardcochran@xxxxxxxxx>
CC: netdev@xxxxxxxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/timekeeping.h |  1 +
 kernel/time/timekeeping.c   | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index fe1e467ba046..5537700ad113 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -43,6 +43,7 @@ extern void ktime_get_ts64(struct timespec64 *ts);
 extern void ktime_get_real_ts64(struct timespec64 *tv);
 extern void ktime_get_coarse_ts64(struct timespec64 *ts);
 extern void ktime_get_coarse_real_ts64(struct timespec64 *ts);
+extern void ktime_get_cycles64(struct timespec64 *ts);
 
 void getboottime64(struct timespec64 *ts);
 
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 266d02809dbb..35d603d21bd5 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -989,6 +989,30 @@ void ktime_get_ts64(struct timespec64 *ts)
 }
 EXPORT_SYMBOL_GPL(ktime_get_ts64);
 
+/**
+ * ktime_get_cycles64 - get the raw clock cycles in timespec64 format
+ * @ts:		pointer to timespec variable
+ *
+ * This function converts the raw clock cycles into timespce64 format
+ * in the varibale pointed to by @ts
+ */
+void ktime_get_cycles64(struct timespec64 *ts)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+	unsigned int seq;
+	u64 now;
+
+	WARN_ON_ONCE(timekeeping_suspended);
+
+	do {
+		seq = read_seqcount_begin(&tk_core.seq);
+		now = tk_clock_read(&tk->tkr_mono);
+	} while (read_seqcount_retry(&tk_core.seq, seq));
+
+	*ts = ns_to_timespec64(now);
+}
+EXPORT_SYMBOL_GPL(ktime_get_cycles64);
+
 /**
  * ktime_get_seconds - Get the seconds portion of CLOCK_MONOTONIC
  *
-- 
2.42.0.582.g8ccd20d70d-goog