time: Introduce one suspend clocksource to compensate the suspend time

On some hardware with multiple clocksources, we have coarse grained
clocksources that support the CLOCK_SOURCE_SUSPEND_NONSTOP flag, but
which are less than ideal for timekeeping whereas other clocksources
can be better candidates but halt on suspend.

Currently, the timekeeping core only supports timing suspend using
CLOCK_SOURCE_SUSPEND_NONSTOP clocksources if that clocksource is the
current clocksource for timekeeping.

As a result, some architectures try to implement read_persistent_clock64()
using those non-stop clocksources, but isn't really ideal, which will
introduce more duplicate code. To fix this, provide logic to allow a
registered SUSPEND_NONSTOP clocksource, which isn't the current
clocksource, to be used to calculate the suspend time.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
[jstultz: minor tweaks to merge with previous resume changes]
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 14 insertions, 8 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 19414b16cf9e..d9e659a12c76 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1692,7 +1692,7 @@ void timekeeping_resume(void)
 	struct clocksource *clock = tk->tkr_mono.clock;
 	unsigned long flags;
 	struct timespec64 ts_new, ts_delta;
-	u64 cycle_now;
+	u64 cycle_now, nsec;
 	bool inject_sleeptime = false;
 
 	read_persistent_clock64(&ts_new);
@@ -1716,13 +1716,8 @@ void timekeeping_resume(void)
 	 * usable source. The rtc part is handled separately in rtc core code.
 	 */
 	cycle_now = tk_clock_read(&tk->tkr_mono);
-	if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
-		cycle_now > tk->tkr_mono.cycle_last) {
-		u64 nsec, cyc_delta;
-
-		cyc_delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
-					      tk->tkr_mono.mask);
-		nsec = mul_u64_u32_shr(cyc_delta, clock->mult, clock->shift);
+	nsec = clocksource_stop_suspend_timing(clock, cycle_now);
+	if (nsec > 0) {
 		ts_delta = ns_to_timespec64(nsec);
 		inject_sleeptime = true;
 	} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
@@ -1757,6 +1752,8 @@ int timekeeping_suspend(void)
 	unsigned long flags;
 	struct timespec64		delta, delta_delta;
 	static struct timespec64	old_delta;
+	struct clocksource *curr_clock;
+	u64 cycle_now;
 
 	read_persistent_clock64(&timekeeping_suspend_time);
 
@@ -1775,6 +1772,15 @@ int timekeeping_suspend(void)
 	timekeeping_forward_now(tk);
 	timekeeping_suspended = 1;
 
+	/*
+	 * Since we've called forward_now, cycle_last stores the value
+	 * just read from the current clocksource. Save this to potentially
+	 * use in suspend timing.
+	 */
+	curr_clock = tk->tkr_mono.clock;
+	cycle_now = tk->tkr_mono.cycle_last;
+	clocksource_start_suspend_timing(curr_clock, cycle_now);
+
 	if (persistent_clock_exists) {
 		/*
 		 * To avoid drift caused by repeated suspend/resumes,