linux-kernel - Re: [PATCH v3 5/7] rtc: New driver for RTC in Netronix embedded controller

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Message-ID: <20200925054424.snlr3lggnsv575wu@pengutronix.de>
Date:   Fri, 25 Sep 2020 07:44:24 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     linux-kernel@...r.kernel.org,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Heiko Stuebner <heiko@...ech.de>, linux-pwm@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Fabio Estevam <festevam@...il.com>, linux-rtc@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Daniel Palmer <daniel@...f.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Andreas Kemnade <andreas@...nade.info>,
        NXP Linux Team <linux-imx@....com>,
        devicetree@...r.kernel.org, Stephan Gerhold <stephan@...hold.net>,
        allen <allen.chen@....com.tw>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Lubomir Rintel <lkundrak@...sk>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Mark Brown <broonie@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Heiko Stuebner <heiko.stuebner@...obroma-systems.com>,
        Josua Mayer <josua.mayer@....eu>,
        Shawn Guo <shawnguo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v3 5/7] rtc: New driver for RTC in Netronix embedded
 controller

Hello Jonathan,

On Thu, Sep 24, 2020 at 09:24:53PM +0200, Jonathan Neuschäfer wrote:
> +#define NTXEC_REG_WRITE_YEAR	0x10
> +#define NTXEC_REG_WRITE_MONTH	0x11
> +#define NTXEC_REG_WRITE_DAY	0x12
> +#define NTXEC_REG_WRITE_HOUR	0x13
> +#define NTXEC_REG_WRITE_MINUTE	0x14
> +#define NTXEC_REG_WRITE_SECOND	0x15
> +
> +#define NTXEC_REG_READ_YM	0x20
> +#define NTXEC_REG_READ_DH	0x21
> +#define NTXEC_REG_READ_MS	0x23

Is this an official naming? I think at least ..._MS is a poor name.
Maybe consider ..._MINSEC instead and make the other two names a bit longer
for consistency?

> +static int ntxec_read_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct ntxec_rtc *rtc = dev_get_drvdata(dev);
> +	unsigned int value;
> +	int res;
> +
> +	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_YM, &value);
> +	if (res < 0)
> +		return res;
> +
> +	tm->tm_year = (value >> 8) + 100;
> +	tm->tm_mon = (value & 0xff) - 1;
> +
> +	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_DH, &value);
> +	if (res < 0)
> +		return res;
> +
> +	tm->tm_mday = value >> 8;
> +	tm->tm_hour = value & 0xff;
> +
> +	res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MS, &value);
> +	if (res < 0)
> +		return res;
> +
> +	tm->tm_min = value >> 8;
> +	tm->tm_sec = value & 0xff;
> +
> +	return 0;
> +}
> +
> +static int ntxec_set_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct ntxec_rtc *rtc = dev_get_drvdata(dev);
> +	int res = 0;
> +
> +	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_YEAR, ntxec_reg8(tm->tm_year - 100));
> +	if (res)
> +		return res;
> +
> +	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_MONTH, ntxec_reg8(tm->tm_mon + 1));
> +	if (res)
> +		return res;
> +
> +	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_DAY, ntxec_reg8(tm->tm_mday));
> +	if (res)
> +		return res;
> +
> +	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_HOUR, ntxec_reg8(tm->tm_hour));
> +	if (res)
> +		return res;
> +
> +	res = regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_MINUTE, ntxec_reg8(tm->tm_min));
> +	if (res)
> +		return res;
> +
> +	return regmap_write(rtc->ec->regmap, NTXEC_REG_WRITE_SECOND, ntxec_reg8(tm->tm_sec));

I wonder: Is this racy? If you write minute, does the seconds reset to
zero or something like that? Or can it happen, that after writing the
minute register and before writing the second register the seconds
overflow and you end up with the time set to a minute later than
intended? If so it might be worth to set the seconds to 0 at the start
of the function (with an explaining comment).

.read_time has a similar race. What happens if minutes overflow between
reading NTXEC_REG_READ_DH and NTXEC_REG_READ_MS?

> +static struct platform_driver ntxec_rtc_driver = {
> +	.driver = {
> +		.name = "ntxec-rtc",
> +	},
> +	.probe = ntxec_rtc_probe,

No .remove function?

> +};
> +module_platform_driver(ntxec_rtc_driver);
> +
> +MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@....net>");
> +MODULE_DESCRIPTION("RTC driver for Netronix EC");
> +MODULE_LICENSE("GPL");

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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