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

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Message-ID: <20170620134827.ubvzhh25klaotupv@piout.net>
Date:   Tue, 20 Jun 2017 15:48:27 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Steve Twiss <stwiss.opensource@...semi.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
        "adi-buildroot-devel@...ts.sourceforge.net" 
        <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-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Michael Chan <michael.chan@...adcom.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "x86@...nel.org" <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>,
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        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" <linux-tegra@...r.kernel.org>,
        "patches@...nsource.wolfsonmicro.com" 
        <patches@...nsource.wolfsonmicro.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 00/51] rtc: stop using rtc deprecated functions

On 20/06/2017 at 15:44:58 +0200, Pavel Machek wrote:
> On Tue 2017-06-20 13:37:22, Steve Twiss wrote:
> > Hi Pavel,
> > 
> > On 20 June 2017 14:26, Pavel Machek wrote:
> > 
> > > 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.
> > 
> > This is it.
> > https://patchwork.kernel.org/patch/6219401/
> 
> Thanks.
> 
> Yes, that's argument against changing rtc _drivers_ for hardware that
> can not do better than 32bit. For generic code (such as 44/51 sysfs,
> 51/51 suspend test), the change still makes sense.
> 

Yes, we agree on that but I won't cherry pick working patches from a 51
patches series.


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