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timekeeping: Correct run-time detection of persistent_clock.
Since commit 31ade30692
, 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.
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Feng Tang <feng.tang@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
[jstultz: Tweaked commit message and subject]
Signed-off-by: John Stultz <john.stultz@linaro.org>
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@ -975,6 +975,14 @@ static int timekeeping_suspend(void)
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read_persistent_clock(&timekeeping_suspend_time);
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/*
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* On some systems the persistent_clock can not be detected at
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* timekeeping_init by its return value, so if we see a valid
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* value returned, update the persistent_clock_exists flag.
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*/
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if (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)
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persistent_clock_exist = true;
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raw_spin_lock_irqsave(&timekeeper_lock, flags);
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write_seqcount_begin(&timekeeper_seq);
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timekeeping_forward_now(tk);
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