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

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Message-ID: <20170620132620.GA16881@amd>
Date:   Tue, 20 Jun 2017 15:26:20 +0200
From:   Pavel Machek <pavel@....cz>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
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 Tue 2017-06-20 14:24:00, Alexandre Belloni wrote:
> 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.

I wanted reference to Russell's mail.

> 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.

Kernel does not know if it has working RTC or not, so it should use
64bit variables. Merging this -- does not hide anything. Yes, some
drivers still may have problems -- so we fix the drivers.

You said:

> > > rtc_time_to_tm will be able to catch it but the 64 bit will
> > > silently ignore it.

If that's the case, we may need 64bit version to be smarter.. but
we'll still need 64bit variables in the kernel.
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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