Commit-ID: 0d6bd9953f739dad96d9a0de65383e479ab4e10d Gitweb: http://git.kernel.org/tip/0d6bd9953f739dad96d9a0de65383e479ab4e10d Author: Zoran Markovic <zoran.markovic@xxxxxxxxxx> AuthorDate: Fri, 17 May 2013 11:24:05 -0700 Committer: John Stultz <john.stultz@xxxxxxxxxx> CommitDate: Tue, 28 May 2013 13:45:19 -0700 timekeeping: Correct run-time detection of persistent_clock. 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. Cc: John Stultz <john.stultz@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Feng Tang <feng.tang@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Zoran Markovic <zoran.markovic@xxxxxxxxxx> [jstultz: Tweaked commit message and subject] Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> --- kernel/time/timekeeping.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 98cd470..baeeb5c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -975,6 +975,14 @@ 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; + raw_spin_lock_irqsave(&timekeeper_lock, flags); write_seqcount_begin(&timekeeper_seq); timekeeping_forward_now(tk); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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