[PATCH v5 3/6] timekeeper: use the extended reading function on snapshot acquiring

[Denis Plotnikov <dplotnikov@virtuozzo.com>]

Make use of the extended reading function on time snapshot getting:
get raw cycles value if extended function is defined.
The raw cycles value then is used for KVM masterclock.

This is a part of the work aiming to move to a more simple scheme of
masterclock related values calculation in KVM

Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 include/linux/timekeeping.h |  3 +++
 kernel/time/timekeeping.c   | 13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 5008e3e..528d088 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -286,6 +286,8 @@ extern void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw,
  * @boot:	Monotonic time since boot
  * @clock_was_set_seq:	The sequence number of clock was set events
  * @cs_was_changed_seq:	The sequence number of clocksource change events
+ * @cycles_valid:	The flag is true when @cycles contain actual
+ *			number of cycles instead some cycle derivative
  */
 struct system_time_snapshot {
 	u64		cycles;
@@ -294,6 +296,7 @@ struct system_time_snapshot {
 	ktime_t		boot;
 	unsigned int	clock_was_set_seq;
 	u8		cs_was_changed_seq;
+	bool		cycles_valid;
 };
 
 /*
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 66f7701..d1aa575 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -957,12 +957,22 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
 	u64 nsec_raw;
 	u64 nsec_real;
 	u64 now;
+	struct clocksource *clock;
 
 	WARN_ON_ONCE(timekeeping_suspended);
 
 	do {
 		seq = read_seqcount_begin(&tk_core.seq);
-		now = tk_clock_read(&tk->tkr_mono);
+		clock = READ_ONCE(tk->tkr_mono.clock);
+		if (clock->read_with_stamp)
+			systime_snapshot->cycles_valid =
+				clock->read_with_stamp(
+					clock, &now, &systime_snapshot->cycles);
+		else {
+			systime_snapshot->cycles_valid = false;
+			now = clock->read(clock);
+			systime_snapshot->cycles = now;
+		}
 		systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;
 		systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;
 		base_real = ktime_add(tk->tkr_mono.base,
@@ -974,7 +984,6 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
 		nsec_raw  = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
 	} while (read_seqcount_retry(&tk_core.seq, seq));
 
-	systime_snapshot->cycles = now;
 	systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
 	systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
 	systime_snapshot->boot = ktime_add_ns(base_boot, nsec_real);
-- 
2.7.4