linux-kernel - [PATCH v3 1/2] time: Don't bother to run rtc

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Date:	Thu, 29 Jan 2015 23:59:06 +0800
From:	Xunlei Pang <xlpang@....com>
To:	linux-kernel@...r.kernel.org
Cc:	rtc-linux@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	John Stultz <john.stultz@...aro.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>
Subject: [PATCH v3 1/2] time: Don't bother to run rtc_resume() for the nonstop clocksource

From: Xunlei Pang <pang.xunlei@...aro.org>

If a system does not provide a persistent_clock(), the time
will be updated on resume by rtc_resume(). With the addition
of the non-stop clocksources for suspend timing, those systems
set the time on resume in timekeeping_resume(), but may not
provide a valid persistent_clock().

This results in the rtc_resume() logic thinking no one has set
the time and it then will over-write the suspend time again,
which is not necessary and only increases clock error.

So, fix this for rtc_resume().

Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>
---
v2->v3:
Refine according to John's comments using internal variable.

 drivers/rtc/class.c         |  2 +-
 include/linux/timekeeping.h |  1 +
 kernel/time/timekeeping.c   | 32 ++++++++++++++++++++------------
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 472a5ad..6100af5 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
 	struct timespec64	sleep_time;
 	int err;
 
-	if (has_persistent_clock())
+	if (timekeeping_sleeptime_injected())
 		return 0;
 
 	rtc_hctosys_ret = -ENODEV;
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 9b63d13..17a460d 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -225,6 +225,7 @@ static inline void timekeeping_clocktai(struct timespec *ts)
 /*
  * RTC specific
  */
+extern bool timekeeping_sleeptime_injected(void);
 extern void timekeeping_inject_sleeptime64(struct timespec64 *delta);
 
 /*
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6a93185..b02133e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1125,12 +1125,26 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
 	tk_debug_account_sleep_time(delta);
 }
 
+static bool sleeptime_inject;
+
+#if defined(CONFIG_RTC_CLASS) && \
+	defined(CONFIG_PM_SLEEP) && \
+	defined(CONFIG_RTC_HCTOSYS_DEVICE)
+/**
+ * Used by rtc_resume().
+ */
+bool timekeeping_sleeptime_injected(void)
+{
+	return sleeptime_inject;
+}
+
 /**
  * timekeeping_inject_sleeptime64 - Adds suspend interval to timeekeeping values
  * @delta: pointer to a timespec64 delta value
  *
  * This hook is for architectures that cannot support read_persistent_clock
- * because their RTC/persistent clock is only accessible when irqs are enabled.
+ * because their RTC/persistent clock is only accessible when irqs are enabled,
+ * and also don't have an effective nonstop clocksource.
  *
  * This function should only be called by rtc_resume(), and allows
  * a suspend offset to be injected into the timekeeping values.
@@ -1140,13 +1154,6 @@ void timekeeping_inject_sleeptime64(struct timespec64 *delta)
 	struct timekeeper *tk = &tk_core.timekeeper;
 	unsigned long flags;
 
-	/*
-	 * Make sure we don't set the clock twice, as timekeeping_resume()
-	 * already did it
-	 */
-	if (has_persistent_clock())
-		return;
-
 	raw_spin_lock_irqsave(&timekeeper_lock, flags);
 	write_seqcount_begin(&tk_core.seq);
 
@@ -1162,6 +1169,7 @@ void timekeeping_inject_sleeptime64(struct timespec64 *delta)
 	/* signal hrtimers about time change */
 	clock_was_set();
 }
+#endif
 
 /**
  * timekeeping_resume - Resumes the generic timekeeping subsystem.
@@ -1178,8 +1186,8 @@ static void timekeeping_resume(void)
 	struct timespec64 ts_new, ts_delta;
 	struct timespec tmp;
 	cycle_t cycle_now, cycle_delta;
-	bool suspendtime_found = false;
 
+	sleeptime_inject = false;
 	read_persistent_clock(&tmp);
 	ts_new = timespec_to_timespec64(tmp);
 
@@ -1226,13 +1234,13 @@ static void timekeeping_resume(void)
 		nsec += ((u64) cycle_delta * mult) >> shift;
 
 		ts_delta = ns_to_timespec64(nsec);
-		suspendtime_found = true;
+		sleeptime_inject = true;
 	} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
 		ts_delta = timespec64_sub(ts_new, timekeeping_suspend_time);
-		suspendtime_found = true;
+		sleeptime_inject = true;
 	}
 
-	if (suspendtime_found)
+	if (sleeptime_inject)
 		__timekeeping_inject_sleeptime(tk, &ts_delta);
 
 	/* Re-base the last cycle value */
-- 
1.9.1


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