linux-kernel - Re: [PATCH] time, Fix setting of hardware clock in NTP code

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Message-ID: <51158643.1020204@linaro.org>
Date:	Fri, 08 Feb 2013 15:12:03 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] time, Fix setting of hardware clock in NTP code

On 02/08/2013 02:59 PM, Prarit Bhargava wrote:
> At init time, if the system time is "warped" forward in warp_clock()
> it will differ from the hardware clock by sys_tz.tz_minuteswest.  This time
> difference is not taken into account when ntp updates the hardware clock,
> and this causes the system time to jump forward by this offset every reboot.
>
> The kernel must take this offset into account when writing the system time
> to the hardware clock in the ntp code.  This patch adds
> persistent_clock_is_local which indicates that an offset has been applied
> in warp_clock() and accounts for the "warp" before writing the hardware
> clock.
>
> x86 does not have this problem as rtc writes are software limited to a
> +/-15 minute window relative to the current rtc time.  Other arches, such
> as powerpc, however do a full synchronization of the system time to the
> rtc and will see this problem.

Ok, I've got this queued in my tree. What sort of testing did you do 
with it?

I want to make sure we don't run into any bad interactions with the 
existing 15min cap on x86.

thanks
-john

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