linux-kernel - Re: [PATCH] rtc: Add support for century bits to m41t62 (rv4162) RTC devices

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Message-ID: <20191003123538.GS4106@piout.net>
Date:   Thu, 3 Oct 2019 14:35:38 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: Add support for century bits to m41t62 (rv4162) RTC
 devices

On 03/10/2019 14:21:50+0200, Lukasz Majewski wrote:
> > 
> > See the datasheet:
> > 
> > "During any year which is a multiple of 4, the RV-4162 RTC will
> > automatically insert leap day, February 29.  Therefore, the
> > application software must correct for this during the exception years
> > (2100, 2200, etc.) as noted above."
> 
> I'm wondering what the phrase "application software" means here?
> 
> If it is the userland SW, then we shall at least be able to set 2099 in
> this device and then count on software correction.
> 
> If the "application software" is the kernel driver - the date
> correction shall be done there (maybe some lookup table?).
> 
> Personally, I do prefer the first option - this means that with this
> patch we can set the time to e.g. 2234 year and then rely on userland
> software (or libc) to do the correction.
> 

It is not possible to ensure this correction is properly done in
software, there is no point in letting the user set those bits.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com