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Date:   Mon, 19 Feb 2018 11:07:54 +0100
From:   Alexandre Belloni <alexandre.belloni@free-electrons.com>
To:     Igor Plyatov <plyatov@gmail.com>
Cc:     Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
        linux-kernel@vger.kernel.org,
        Alessandro Zummo <a.zummo@towertech.it>,
        rtc-linux@googlegroups.com, util-linux@vger.kernel.org
Subject: Re: 500 ms delay in time saved into RTC
Message-ID: <20180219100754.GL14177@piout.net>
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On 19/02/2018 at 12:16:04 +0300, Igor Plyatov wrote:
> Dear Rasmus,
> 
> thank you very much for explanation!
> 
> I have set "RTC_SET_DELAY_SECS = 0.0" in hwclock.c and got acceptable
> result.
> 
> It wonder why such critical function does not implemented on kernel level in
> RTC driver?
> It is very strange to rely on specific HW in user space SW.
> 

Because of the way the API is designed, handling the MC146818A oddity is
not possible in the driver (i.e. 50% of the time, it will be too late
to handle it).

You can use busybox hwclock which has the x86 insanity commented out:
https://git.busybox.net/busybox/tree/util-linux/hwclock.c


-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com