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authorZoran Markovic <zoran.markovic@linaro.org>2013-05-17 11:24:05 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-06-13 10:49:52 -0700
commit054b50539d3dac99c5454e612e541c1f351a38b1 (patch)
tree9cc2a573cc5d9593495da1172a60e4d7659522c0
parentdaa61456b3c3764704fe7f5ae616d6d02bdbaeef (diff)
downloadlinaro-lsk-054b50539d3dac99c5454e612e541c1f351a38b1.tar.gz
timekeeping: Correct run-time detection of persistent_clock.
commit 0d6bd9953f739dad96d9a0de65383e479ab4e10d upstream. Since commit 31ade30692dc9680bfc95700d794818fa3f754ac, timekeeping_init() checks for presence of persistent clock by attempting to read a non-zero time value. This is an issue on platforms where persistent_clock (instead is implemented as a free-running counter (instead of an RTC) starting from zero on each boot and running during suspend. Examples are some ARM platforms (e.g. PandaBoard). An attempt to read such a clock during timekeeping_init() may return zero value and falsely declare persistent clock as missing. Additionally, in the above case suspend times may be accounted twice (once from timekeeping_resume() and once from rtc_resume()), resulting in a gradual drift of system time. This patch does a run-time correction of the issue by doing the same check during timekeeping_suspend(). A better long-term solution would have to return error when trying to read non-existing clock and zero when trying to read an uninitialized clock, but that would require changing all persistent_clock implementations. This patch addresses the immediate breakage, for now. Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org> Cc: John Stultz <john.stultz@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Feng Tang <feng.tang@intel.com> [jstultz: Tweaked commit message and subject] Signed-off-by: John Stultz <john.stultz@linaro.org> [zoran.markovic@linaro.org: reworked patch to fit 3.9-stable.] Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/time/timekeeping.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 9a0bc98fbe1..183df62de9e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -826,6 +826,14 @@ static int timekeeping_suspend(void)
read_persistent_clock(&timekeeping_suspend_time);
+ /*
+ * On some systems the persistent_clock can not be detected at
+ * timekeeping_init by its return value, so if we see a valid
+ * value returned, update the persistent_clock_exists flag.
+ */
+ if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
+ persistent_clock_exist = true;
+
write_seqlock_irqsave(&tk->lock, flags);
timekeeping_forward_now(tk);
timekeeping_suspended = 1;