From 054b50539d3dac99c5454e612e541c1f351a38b1 Mon Sep 17 00:00:00 2001 From: Zoran Markovic Date: Fri, 17 May 2013 11:24:05 -0700 Subject: 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 Cc: John Stultz Cc: Thomas Gleixner Cc: Feng Tang [jstultz: Tweaked commit message and subject] Signed-off-by: John Stultz [zoran.markovic@linaro.org: reworked patch to fit 3.9-stable.] Signed-off-by: Zoran Markovic Signed-off-by: Greg Kroah-Hartman --- kernel/time/timekeeping.c | 8 ++++++++ 1 file changed, 8 insertions(+) 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; -- cgit v1.2.3