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Subject[PATCH v4 3/4] time: rtc: Don't bother into rtc_resume() for the nonstop clocksource
Date
From: Xunlei Pang <pang.xunlei@linaro.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@linaro.org>
---
drivers/rtc/class.c | 4 +--
include/linux/timekeeping.h | 9 +++----
kernel/time/timekeeping.c | 63 +++++++++++++++++++++++++++++++++------------
3 files changed, 52 insertions(+), 24 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 472a5ad..74a943e 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -55,7 +55,7 @@ static int rtc_suspend(struct device *dev)
struct timespec64 delta, delta_delta;
int err;

- if (has_persistent_clock())
+ if (timekeeping_rtc_skipsuspend())
return 0;

if (strcmp(dev_name(&rtc->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)
@@ -102,7 +102,7 @@ static int rtc_resume(struct device *dev)
struct timespec64 sleep_time;
int err;

- if (has_persistent_clock())
+ if (timekeeping_rtc_skipresume())
return 0;

rtc_hctosys_ret = -ENODEV;
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 3eaae47..7cbd518 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -242,6 +242,9 @@ static inline void timekeeping_clocktai(struct timespec *ts)
/*
* RTC specific
*/
+extern bool timekeeping_rtc_skipsuspend(void);
+extern bool timekeeping_rtc_skipresume(void);
+
extern void timekeeping_inject_sleeptime64(struct timespec64 *delta);

/*
@@ -253,14 +256,8 @@ extern void getnstime_raw_and_real(struct timespec *ts_raw,
/*
* Persistent clock related interfaces
*/
-extern bool persistent_clock_exist;
extern int persistent_clock_is_local;

-static inline bool has_persistent_clock(void)
-{
- return persistent_clock_exist;
-}
-
extern void read_persistent_clock(struct timespec *ts);
extern void read_boot_clock(struct timespec *ts);
extern int update_persistent_clock(struct timespec now);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ec6ee9b..276c72d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -63,9 +63,6 @@ static struct tk_fast tk_fast_mono ____cacheline_aligned;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;

-/* Flag for if there is a persistent clock on this platform */
-bool __read_mostly persistent_clock_exist = false;
-
static inline void tk_normalize_xtime(struct timekeeper *tk)
{
while (tk->tkr.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr.shift)) {
@@ -1045,6 +1042,9 @@ void __weak read_boot_clock(struct timespec *ts)
ts->tv_nsec = 0;
}

+/* Flag for if there is a persistent clock on this platform */
+static bool persistent_clock_exist;
+
/*
* timekeeping_init - Initializes the clocksource and common timekeeping values
*/
@@ -1125,15 +1125,53 @@ 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)
/**
+ * We have three kinds of time sources to use for sleep time
+ * injection, the preference order is:
+ * 1) non-stop clocksource
+ * 2) persistent clock (ie: RTC accessible when irqs are off)
+ * 3) RTC
+ *
+ * 1) and 2) are used by timekeeping, 3) by RTC subsystem.
+ * If system has neither 1) nor 2), 3) will be used finally.
+ *
+ *
+ * If timekeeping has injected sleeptime via either 1) or 2),
+ * 3) becomes needless, so in this case we don't need to call
+ * rtc_resume(), and this is what timekeeping_rtc_skipresume()
+ * means.
+ */
+bool timekeeping_rtc_skipresume(void)
+{
+ return sleeptime_inject;
+}
+
+/**
+ * 1) can be determined whether to use or not only when doing
+ * timekeeping_resume() which is invoked after rtc_suspend(),
+ * so we can't skip rtc_suspend() surely if system has 1).
+ *
+ * But if system has 2), 2) will definitely be used, so in this
+ * case we don't need to call rtc_suspend(), and this is what
+ * timekeeping_rtc_skipsuspend() means.
+ */
+bool timekeeping_rtc_skipsuspend(void)
+{
+ return persistent_clock_exist;
+}
+
+/**
* 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.
@@ -1143,13 +1181,6 @@ 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);

@@ -1182,8 +1213,8 @@ 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);

@@ -1230,14 +1261,14 @@ 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,
&persistent_clock_suspendtime) > 0) {
ts_delta = timespec64_sub(ts_new, persistent_clock_suspendtime);
- suspendtime_found = true;
+ sleeptime_inject = true;
}

- if (suspendtime_found)
+ if (sleeptime_inject)
__timekeeping_inject_sleeptime(tk, &ts_delta);

/* Re-base the last cycle value */
@@ -1281,7 +1312,7 @@ static int timekeeping_suspend(void)
timekeeping_forward_now(tk);
timekeeping_suspended = 1;

- if (has_persistent_clock()) {
+ if (persistent_clock_exist) {
/*
* To avoid drift caused by repeated suspend/resumes,
* which each can add ~1 second drift error,
--
1.9.1



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