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authorThomas Gleixner <tglx@linutronix.de>2007-09-16 09:36:43 -0400
committerThomas Gleixner <tglx@chaos.(none)>2007-09-16 09:36:43 -0400
commit6a669ee8a790487b7ec1edda762d39615a78264b (patch)
tree487270be1b035d75622f0f9b1e34f1c6b2cfbeae /kernel/time
parent3be9095063885d482b87d3875ea7f28e635882d0 (diff)
timekeeping: Prevent time going backwards on resume
Timekeeping resume adjusts xtime by adding the slept time in seconds and resets the reference value of the clock source (clock->cycle_last). clock->cycle last is used to calculate the delta between the last xtime update and the readout of the clock source in __get_nsec_offset(). xtime plus the offset is the current time. The resume code ignores the delta which had already elapsed between the last xtime update and the actual time of suspend. If the suspend time is short, then we can see time going backwards on resume. Suspend: offs_s = clock->read() - clock->cycle_last; now = xtime + offs_s; timekeeping_suspend_time = read_rtc(); Resume: sleep_time = read_rtc() - timekeeping_suspend_time; xtime.tv_sec += sleep_time; clock->cycle_last = clock->read(); offs_r = clock->read() - clock->cycle_last; now = xtime + offs_r; if sleep_time_seconds == 0 and offs_r < offs_s, then time goes backwards. Fix this by storing the offset from the last xtime update and add it to xtime during resume, when we reset clock->cycle_last: sleep_time = read_rtc() - timekeeping_suspend_time; xtime.tv_sec += sleep_time; xtime += offs_s; /* Fixup xtime offset at suspend time */ clock->cycle_last = clock->read(); offs_r = clock->read() - clock->cycle_last; now = xtime + offs_r; Thanks to Marcelo for tracking this down on the OLPC and providing the necessary details to analyze the root cause. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: John Stultz <johnstul@us.ibm.com> Cc: Tosatti <marcelo@kvack.org>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/timekeeping.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index f682091fa890..4ad79f6bdec6 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -217,6 +217,7 @@ static void change_clocksource(void)
217} 217}
218#else 218#else
219static inline void change_clocksource(void) { } 219static inline void change_clocksource(void) { }
220static inline s64 __get_nsec_offset(void) { return 0; }
220#endif 221#endif
221 222
222/** 223/**
@@ -280,6 +281,8 @@ void __init timekeeping_init(void)
280static int timekeeping_suspended; 281static int timekeeping_suspended;
281/* time in seconds when suspend began */ 282/* time in seconds when suspend began */
282static unsigned long timekeeping_suspend_time; 283static unsigned long timekeeping_suspend_time;
284/* xtime offset when we went into suspend */
285static s64 timekeeping_suspend_nsecs;
283 286
284/** 287/**
285 * timekeeping_resume - Resumes the generic timekeeping subsystem. 288 * timekeeping_resume - Resumes the generic timekeeping subsystem.
@@ -305,6 +308,8 @@ static int timekeeping_resume(struct sys_device *dev)
305 wall_to_monotonic.tv_sec -= sleep_length; 308 wall_to_monotonic.tv_sec -= sleep_length;
306 total_sleep_time += sleep_length; 309 total_sleep_time += sleep_length;
307 } 310 }
311 /* Make sure that we have the correct xtime reference */
312 timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
308 /* re-base the last cycle value */ 313 /* re-base the last cycle value */
309 clock->cycle_last = clocksource_read(clock); 314 clock->cycle_last = clocksource_read(clock);
310 clock->error = 0; 315 clock->error = 0;
@@ -328,6 +333,8 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
328 timekeeping_suspend_time = read_persistent_clock(); 333 timekeeping_suspend_time = read_persistent_clock();
329 334
330 write_seqlock_irqsave(&xtime_lock, flags); 335 write_seqlock_irqsave(&xtime_lock, flags);
336 /* Get the current xtime offset */
337 timekeeping_suspend_nsecs = __get_nsec_offset();
331 timekeeping_suspended = 1; 338 timekeeping_suspended = 1;
332 write_sequnlock_irqrestore(&xtime_lock, flags); 339 write_sequnlock_irqrestore(&xtime_lock, flags);
333 340