Messages in this thread | | | From | Shuah Khan <> | Subject | Re: pm: System date and time set incorrectly after suspend/resume to disk | Date | Tue, 18 Jun 2013 18:14:02 +0000 |
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On 06/17/2013 08:14 PM, John Stultz wrote: > On Mon, Jun 17, 2013 at 6:30 PM, Shuah Khan <shuah.kh@samsung.com> wrote: >> I am seeing a problem on my system after a suspend to disk in reboot or >> shutdown mode. When pm_trace is 0 (which is the default), I can't >> reproduce the problem easily. I have to run a few more suspend tests >> before I see the problem. When pm_trace is disabled, the problem showed >> up when I ran suspend in platform mode in a row. However when pm_ptrace >> is enabled, problem happens on the very first spend to disk in reboot mode. >> >> Steps to run into the issue: >> >> echo 1 > pm_print_times >> echo 1 > pm_trace >> echo reboot > disk >> echo disk > state >> >> or >> >> echo 1 > pm_print_times >> echo 1 > pm_trace >> echo shutdown > disk >> echo disk > state >> >> When system comes back up, system time set to incorrect time. > > So I this is by design. Please see Documentation/power/s2ram.txt for details: > > "pm_trace uses the system's Real Time Clock (RTC) to save the magic number. > Reason for this is that the RTC is the only reliably available piece of > hardware during resume operations where a value can be set that will > survive a reboot. > > Consequence is that after a resume (even if it is successful) your system > clock will have a value corresponding to the magic number instead of the > correct date/time! It is therefore advisable to use a program like ntp-date > or rdate to reset the correct date/time from an external time source when > using this trace option." > > thanks > -john >
Thanks. It definitely is working as designed and documented. :) Is there a reason why pm_trace_store() couldn't/shouldn't print a warning message (pr_warn) along the lines of:
"CAUTION: this option will cause your machine's real-time clock to be set to an invalid time after a resume. Remember to set correct time after resume!!"
It will serve as a reminder to correct the time after resume. I could send a patch in to add a warning message.
thanks, -- Shuah
Shuah Khan, Linux Kernel Developer - Open Source Group Samsung Research America (Silicon Valley) shuah.kh@samsung.com | (970) 672-0658
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