linux-kernel - Re: [PATCH 00/51] rtc: stop using rtc deprecated functions

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Message-ID: <20170620122400.sm7qqvwyj6cuzarw@piout.net>
Date:   Tue, 20 Jun 2017 14:24:00 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        linaro-kernel@...ts.linaro.org,
        adi-buildroot-devel@...ts.sourceforge.net,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Cooper <jason@...edaemon.net>,
        John Stultz <john.stultz@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Michael Chan <michael.chan@...adcom.com>,
        netdev@...r.kernel.org, rtc-linux@...glegroups.com,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Support Opensource <support.opensource@...semi.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        Baruch Siach <baruch@...s.co.il>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Sylvain Lemieux <slemieux.tyco@...il.com>,
        Barry Song <baohua@...nel.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, patches@...nsource.wolfsonmicro.com,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 00/51] rtc: stop using rtc deprecated functions

On 20/06/2017 at 14:10:11 +0200, Pavel Machek wrote:
> On Tue 2017-06-20 12:03:48, Alexandre Belloni wrote:
> > On 20/06/2017 at 11:35:08 +0200, Benjamin Gaignard wrote:
> > > rtc_time_to_tm() and rtc_tm_to_time() are deprecated because they
> > > rely on 32bits variables and that will make rtc break in y2038/2016.
> > 
> > Please don't, because this hide the fact that the hardware will not
> > handle dates in y2038 anyway and as pointed by Russell a few month ago,
> > rtc_time_to_tm will be able to catch it but the 64 bit version will
> > silently ignore it.
> 
> Reference? Because rtc on PCs stores date in binary coded decimal, so
> it is likely to break in 2100, not 2038...

I'm not saying it should be done but clearly, that is not the correct
thing to do for RTCs that are using a single 32 bits register to store
the time.
You give one example, I can give you three: armada38x, at91sam9,
at32ap700x and that just in the beginning of the series.

And yes, on PC, they will break in 2100, other in 2106, some in 2070.
I've delayed the tree wide patching until I manage to finish reworking
the infrastructure needed to handle the limits of the RTCs.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com