| Message ID | 1372285655-2450-1-git-send-email-shuah.kh@samsung.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Wed 2013-06-26 16:27:35, Shuah Khan wrote: > 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. > > There is no run-time message to warn users of the consequences of enabling > pm_trace. Adding a warning message to pm_trace_store() will serve as a > reminder to users to set the system date and time after resume. > > Signed-off-by: Shuah Khan <shuah.kh@samsung.com> Acked-by: Pavel Machek <pavel@ucw.cz>
On Thursday, June 27, 2013 01:18:08 AM Pavel Machek wrote: > On Wed 2013-06-26 16:27:35, Shuah Khan wrote: > > 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. > > > > There is no run-time message to warn users of the consequences of enabling > > pm_trace. Adding a warning message to pm_trace_store() will serve as a > > reminder to users to set the system date and time after resume. > > > > Signed-off-by: Shuah Khan <shuah.kh@samsung.com> > > Acked-by: Pavel Machek <pavel@ucw.cz> Queued up for 3.11. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/kernel/power/main.c b/kernel/power/main.c index d77663b..480fe06 100644 --- a/kernel/power/main.c +++ b/kernel/power/main.c @@ -528,6 +528,10 @@ pm_trace_store(struct kobject *kobj, struct kobj_attribute *attr, if (sscanf(buf, "%d", &val) == 1) { pm_trace_enabled = !!val; + if (pm_trace_enabled) { + pr_warn("PM: Enabling pm_trace changes system date and time during resume.\n" + "PM: Correct system time has to be restored manually after resume.\n"); + } return n; } return -EINVAL;
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. There is no run-time message to warn users of the consequences of enabling pm_trace. Adding a warning message to pm_trace_store() will serve as a reminder to users to set the system date and time after resume. Signed-off-by: Shuah Khan <shuah.kh@samsung.com> --- kernel/power/main.c | 4 ++++ 1 file changed, 4 insertions(+)