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authorFeng Tang <feng.tang@intel.com>2013-03-12 11:56:48 +0800
committerJohn Stultz <john.stultz@linaro.org>2013-03-15 16:51:29 -0700
commite445cf1c4257cc0238d72e4129eb4739f46fd3de (patch)
tree5ff9c120a867939996d83dae6e885e81177c1819 /kernel/time/timekeeping.c
parent82f9c080b22a5b859ae2b50822dfb6b812898fdb (diff)
downloadlinaro-lsk-e445cf1c4257cc0238d72e4129eb4739f46fd3de.tar.gz
timekeeping: utilize the suspend-nonstop clocksource to count suspended time
There are some new processors whose TSC clocksource won't stop during suspend. Currently, after system resumes, kernel will use persistent clock or RTC to compensate the sleep time, but with these nonstop clocksources, we could skip the special compensation from external sources, and just use current clocksource for time recounting. This can solve some time drift bugs caused by some not-so-accurate or error-prone RTC devices. The current way to count suspended time is first try to use the persistent clock, and then try the RTC if persistent clock can't be used. This patch will change the trying order to: suspend-nonstop clocksource -> persistent clock -> RTC When counting the sleep time with nonstop clocksource, use an accurate way suggested by Jason Gunthorpe to cover very large delta cycles. Signed-off-by: Feng Tang <feng.tang@intel.com> [jstultz: Small optimization, avoiding re-reading the clocksource] Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'kernel/time/timekeeping.c')
-rw-r--r--kernel/time/timekeeping.c58
1 files changed, 51 insertions, 7 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 9a0bc98fbe1..0355f125d58 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -788,22 +788,66 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
static void timekeeping_resume(void)
{
struct timekeeper *tk = &timekeeper;
+ struct clocksource *clock = tk->clock;
unsigned long flags;
- struct timespec ts;
+ struct timespec ts_new, ts_delta;
+ cycle_t cycle_now, cycle_delta;
+ bool suspendtime_found = false;
- read_persistent_clock(&ts);
+ read_persistent_clock(&ts_new);
clockevents_resume();
clocksource_resume();
write_seqlock_irqsave(&tk->lock, flags);
- if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
- ts = timespec_sub(ts, timekeeping_suspend_time);
- __timekeeping_inject_sleeptime(tk, &ts);
+ /*
+ * After system resumes, we need to calculate the suspended time and
+ * compensate it for the OS time. There are 3 sources that could be
+ * used: Nonstop clocksource during suspend, persistent clock and rtc
+ * device.
+ *
+ * One specific platform may have 1 or 2 or all of them, and the
+ * preference will be:
+ * suspend-nonstop clocksource -> persistent clock -> rtc
+ * The less preferred source will only be tried if there is no better
+ * usable source. The rtc part is handled separately in rtc core code.
+ */
+ cycle_now = clock->read(clock);
+ if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
+ cycle_now > clock->cycle_last) {
+ u64 num, max = ULLONG_MAX;
+ u32 mult = clock->mult;
+ u32 shift = clock->shift;
+ s64 nsec = 0;
+
+ cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
+
+ /*
+ * "cycle_delta * mutl" may cause 64 bits overflow, if the
+ * suspended time is too long. In that case we need do the
+ * 64 bits math carefully
+ */
+ do_div(max, mult);
+ if (cycle_delta > max) {
+ num = div64_u64(cycle_delta, max);
+ nsec = (((u64) max * mult) >> shift) * num;
+ cycle_delta -= num * max;
+ }
+ nsec += ((u64) cycle_delta * mult) >> shift;
+
+ ts_delta = ns_to_timespec(nsec);
+ suspendtime_found = true;
+ } else if (timespec_compare(&ts_new, &timekeeping_suspend_time) > 0) {
+ ts_delta = timespec_sub(ts_new, timekeeping_suspend_time);
+ suspendtime_found = true;
}
- /* re-base the last cycle value */
- tk->clock->cycle_last = tk->clock->read(tk->clock);
+
+ if (suspendtime_found)
+ __timekeeping_inject_sleeptime(tk, &ts_delta);
+
+ /* Re-base the last cycle value */
+ clock->cycle_last = cycle_now;
tk->ntp_error = 0;
timekeeping_suspended = 0;
timekeeping_update(tk, false);