linux-kernel - Re: [bugreport] "hwclock -w" reset time instead of setting the right time

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Message-ID: <nycvar.YAK.7.76.2001021153220.1385@zhn.tzk.pbz>
Date:   Thu, 2 Jan 2020 11:58:58 -0500 (EST)
From:   J William Piggott <elseifthen@....com>
To:     Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
cc:     Karel Zak <kzak@...hat.com>, util-linux@...r.kernel.org,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        linux-rtc@...r.kernel.org
Subject: Re: [bugreport] "hwclock -w" reset time instead of setting the right
 time



On Thu, 2 Jan 2020, Mikhail Gavrilov wrote:

> On Thu, 2 Jan 2020 at 18:14, Karel Zak <kzak@...hat.com> wrote:
>>
>> At first glance it seems hwclock works as expected, I do not see
>> anything wrong in the output.
>>
>>> Demonstration: https://youtu.be/Yx27IH2opEc
>>
>> What is hw time before reboot? Can you verify that hwclock reset the
>> clock? (or is it system reboot?)
>>
>>     # hwclock -w -v
>>     # hwclock -v
>>
>> Do you see anything interesting in dmesg output before reboot and after
>> hwclock -w?
>>
>>
>
> Yes, before reboot all look like good:
>
> [root@...alhost ~]# hwclock -v
> hwclock from util-linux 2.35-rc1-20-63f8
> System Time: 1577977370.909455
> Trying to open: /dev/rtc0
> Using the rtc interface to the clock.
> Last drift adjustment done at 1577973311 seconds after 1969
> Last calibration done at 1577973311 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> ...got clock tick
> Time read from Hardware Clock: 2020/01/02 15:02:52
> Hw clock time : 2020/01/02 15:02:52 = 1577977372 seconds since 1969
> Time since last adjustment is 4061 seconds
> Calculated Hardware Clock drift is 0.000000 seconds
> 2020-01-02 20:02:51.077494+05:00
>
>
> [root@...alhost ~]# hwclock -w -v
> hwclock from util-linux 2.35-rc1-20-63f8
> System Time: 1577977383.789039
> Trying to open: /dev/rtc0
> Using the rtc interface to the clock.
> Last drift adjustment done at 1577973311 seconds after 1969
> Last calibration done at 1577973311 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> RTC type: 'rtc_cmos'
> Using delay: 0.500000 seconds
> missed it - 1577977383.789405 is too far past 1577977383.500000
> (0.289405 > 0.001000)
> 1577977384.500000 is close enough to 1577977384.500000 (0.000000 < 0.002000)
> Set RTC to 1577977384 (1577977383 + 1; refsystime = 1577977383.000000)
> Setting Hardware Clock to 15:03:04 = 1577977384 seconds since 1969
> ioctl(RTC_SET_TIME) was successful.
> Not adjusting drift factor because the --update-drift option was not used.
> New /etc/adjtime data:
> 0.000000 1577977383 0.000000
> 1577977383
> UTC
>
>
> [root@...alhost ~]# hwclock -v
> hwclock from util-linux 2.35-rc1-20-63f8
> System Time: 1577977389.540630
> Trying to open: /dev/rtc0
> Using the rtc interface to the clock.
> Last drift adjustment done at 1577977383 seconds after 1969
> Last calibration done at 1577977383 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> ...got clock tick
> Time read from Hardware Clock: 2020/01/02 15:03:10
> Hw clock time : 2020/01/02 15:03:10 = 1577977390 seconds since 1969
> Time since last adjustment is 7 seconds
> Calculated Hardware Clock drift is 0.000000 seconds
> 2020-01-02 20:03:09.718222+05:00
>
> But after reboot, the hwtime is reset:
>
> === Reboot ===
>
>
> [root@...alhost ~]# hwclock -v
> hwclock from util-linux 2.35-rc1-20-63f8
> System Time: 1576407103.342223
> Trying to open: /dev/rtc0
> Using the rtc interface to the clock.
> Last drift adjustment done at 1577977383 seconds after 1969
> Last calibration done at 1577977383 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> ...got clock tick
> Time read from Hardware Clock: 2019/01/01 00:05:31
> Hw clock time : 2019/01/01 00:05:31 = 1546301131 seconds since 1969
> Time since last adjustment is -31676252 seconds
> Calculated Hardware Clock drift is 0.000000 seconds
> 2019-01-01 05:05:30.170661+05:00
>
> [root@...alhost ~]# date
> Sun 15 Dec 2019 03:52:01 PM +05
>
>
> Demonstration: https://youtu.be/X0w2hbAmKmM

You've demonstrated that 'hwclock -w' does not 'reset' the RTC.

Does your new motherboard use a battery backup for the RTC?
Is the battery good?

>
>
> --
> Best Regards,
> Mike Gavrilov.
>