|author||Zoran Markovic <email@example.com>||2013-05-17 11:24:05 -0700|
|committer||John Stultz <firstname.lastname@example.org>||2013-05-28 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 <email@example.com> Cc: Thomas Gleixner <firstname.lastname@example.org> Cc: Feng Tang <email@example.com> Cc: firstname.lastname@example.org Signed-off-by: Zoran Markovic <email@example.com> [jstultz: Tweaked commit message and subject] Signed-off-by: John Stultz <firstname.lastname@example.org>
Diffstat (limited to 'kernel/time')
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 98cd470bbe4..baeeb5c87cf 100644
@@ -975,6 +975,14 @@ static int timekeeping_suspend(void)
+ * 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;