Re: [PATCH 3/7] rtc: rzn1: Add new RTC driver

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>,
	Rob Herring <robh+dt@kernel.org>,
	devicetree@vger.kernel.org,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	linux-renesas-soc@vger.kernel.org,
	Magnus Damm <magnus.damm@gmail.com>,
	Gareth Williams <gareth.williams.jx@renesas.com>,
	Phil Edworthy <phil.edworthy@renesas.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	linux-clk@vger.kernel.org,
	Milan Stevanovic <milan.stevanovic@se.com>,
	Jimmy Lalande <jimmy.lalande@se.com>,
	Pascal Eberhard <pascal.eberhard@se.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Herve Codina <herve.codina@bootlin.com>,
	Clement Leger <clement.leger@bootlin.com>,
	linux-rtc@vger.kernel.org,
	Michel Pollet <michel.pollet@bp.renesas.com>
Subject: Re: [PATCH 3/7] rtc: rzn1: Add new RTC driver
Date: Thu, 14 Apr 2022 13:19:32 +0200	[thread overview]
Message-ID: <20220414131932.5f5285d4@xps13> (raw)
In-Reply-To: <Ylbw3bEc+QK4m9hX@mail.local>

Hi Alex,

alexandre.belloni@bootlin.com wrote on Wed, 13 Apr 2022 17:48:45 +0200:

> Hi Miquèl,
> 
> On 13/04/2022 17:23:27+0200, Miquel Raynal wrote:
> > > > +static int rzn1_rtc_probe(struct platform_device *pdev)
> > > > +{
> > > > +	struct rzn1_rtc *rtc;
> > > > +	int ret;
> > > > +
> > > > +	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
> > > > +	if (!rtc)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	platform_set_drvdata(pdev, rtc);
> > > > +
> > > > +	rtc->clk = devm_clk_get(&pdev->dev, "hclk");
> > > > +	if (IS_ERR(rtc->clk))
> > > > +		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->clk), "Missing hclk\n");
> > > > +
> > > > +	rtc->base = devm_platform_ioremap_resource(pdev, 0);
> > > > +	if (IS_ERR(rtc->base))
> > > > +		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->base), "Missing reg\n");
> > > > +
> > > > +	rtc->rtcdev = devm_rtc_allocate_device(&pdev->dev);
> > > > +	if (IS_ERR(rtc->rtcdev))
> > > > +		return PTR_ERR(rtc);
> > > > +
> > > > +	rtc->rtcdev->range_max = 3178591199UL; /* 100 years */    
> > > 
> > > I'm not sure how you came to this value, this is 2070-09-22T05:59:59.
> > > I'm pretty sure the RTC will not fail at that time. Also, the comment
> > > seems fishy.  
> > 
> > The RTC itself as no "starting point", but just a counter that can
> > count up to 100. So the max range is start-year + 100 years. But at
> > this point I don't yet have access to the start-year value. What's
> > your advise?  
> 
> The question is why is this limited to 100 years? My guess is that it
> doesn't handle leap years properly if this is the case, there is only
> one range that works, this is 2000-01-01 to 2099-12-31 like many other
> RTCs.

I don't know the real reason, actually there is just written that the
"year" register counts up from 00 to 99 (in bcd).

> You can run rtc-range from rtc-tools after removing range_max to find
> out.

Here is the result. It fails at 2069, which I believe means "100 years"
from 1970. So what do you conclude with this? Shall I use
rtc_time64_to_tm(2069-12-31 23:59:59) as the range_max value?

# rtc-range 

Testing 2000-02-28 23:59:59.
OK

Testing 2038-01-19 03:14:07.
OK

Testing 2069-12-31 23:59:59.
KO RTC_RD_TIME returned 22 (line 124)

Thanks,
Miquèl