linux-kernel - Re: pm_trace displays the wrong time from the RTC

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Date:	Tue, 31 Jul 2007 14:39:39 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: pm_trace displays the wrong time from the RTC

On Tue, 31 Jul 2007 17:20:10 -0400 Chuck Ebbert wrote:

> When resuming, systems print this when booted on 07/31/07:
> 
> Date: 06/31/107
> 
> /drivers/base/power/trace.c::read_magic_time():
> 114	get_rtc_time(&time);
> 115	printk("Time: %2d:%02d:%02d Date: %02d/%02d/%02d\n",
> 116		time.tm_hour, time.tm_min, time.tm_sec,
> 117		time.tm_mon, time.tm_mday, time.tm_year);
> 
> include/asm-generic/rtc.h:
> 102         /*
> 103          * Account for differences between how the RTC uses the values
> 104          * and how they are defined in a struct rtc_time;
> 105          */
> 106         if (time->tm_year <= 69)
> 107                 time->tm_year += 100;
> 108 
> 109         time->tm_mon--;


That's this config option (read all of it):

config PM_TRACE
	bool "Suspend/resume event tracing"
	depends on PM_DEBUG && X86 && EXPERIMENTAL
	default n
	---help---
	This enables some cheesy code to save the last PM event point in the
	RTC across reboots, so that you can debug a machine that just hangs
	during suspend (or more commonly, during resume).

	To use this debugging feature you should attempt to suspend the machine,
	then reboot it, then run

		dmesg -s 1000000 | grep 'hash matches'

	CAUTION: this option will cause your machine's real-time clock to be
	set to an invalid time after a resume.


---
~Randy
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