From 9dceefe483d7640ba0bbf3e53d1db880e7469aba Mon Sep 17 00:00:00 2001 From: Shuah Khan Date: Wed, 26 Jun 2013 16:27:35 -0600 Subject: PM / Sleep: Warn about system time after resume with pm_trace pm_trace uses the system's Real Time Clock (RTC) to save the magic number. The 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 Acked-by: Pavel Machek Signed-off-by: Rafael J. Wysocki --- kernel/power/main.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'kernel/power') diff --git a/kernel/power/main.c b/kernel/power/main.c index 0828070d38b4..1d1bf630e6e9 100644 --- a/kernel/power/main.c +++ b/kernel/power/main.c @@ -530,6 +530,10 @@ 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; -- cgit v1.2.3