[v2,2/2] rtc: add driver for RX6110SA real time clock

The RX6110 comes in two different variants: SPI and I2C.
This driver only supports the SPI variant.

If the need ever arises to also support the I2C variant, this driver
could easily be refactored to support both cases.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
---
Changes since v1:
	- fixed y2k38 problem
	- changed compatible
	- rebased to rtc-next

 drivers/rtc/Kconfig      |   9 +
 drivers/rtc/Makefile     |   1 +
 drivers/rtc/rtc-rx6110.c | 480 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 490 insertions(+)
 create mode 100644 drivers/rtc/rtc-rx6110.c

Hi,

Thanks for that patch, I'm sorry I didn't find the time to reply to your
previous version.

On 01/12/2015 at 14:48:20 +0100, Steffen Trumtrar wrote :
> diff --git a/drivers/rtc/rtc-rx6110.c b/drivers/rtc/rtc-rx6110.c
> new file mode 100644
> index 000000000000..7a828adf9794
> --- /dev/null
> +++ b/drivers/rtc/rtc-rx6110.c
> @@ -0,0 +1,480 @@
> +/*
> + * Driver for the Epson RTC module RX-6110 SA
> + *
> + * Copyright(C) 2015 Pengutronix, Steffen Trumtrar <kernel@pengutronix.de>
> + * Copyright(C) SEIKO EPSON CORPORATION 2013. All rights reserved.
> + *
> + * Derived from RX-8025 driver:
> + * Copyright (C) 2009 Wolfgang Grandegger <wg@grandegger.com>
> + *
> + * Copyright (C) 2005 by Digi International Inc.
> + * All rights reserved.
> + *
> + * Modified by fengjh at rising.com.cn
> + * <http://lists.lm-sensors.org/mailman/listinfo/lm-sensors>
> + * 2006.11
> + *
> + * Code cleanup by Sergei Poselenov, <sposelenov@emcraft.com>
> + * Converted to new style by Wolfgang Grandegger <wg@grandegger.com>
> + * Alarm and periodic interrupt added by Dmitry Rakhchev <rda@emcraft.com>
> + *
> + *

Please remove all those unnecessary copyrights and credits. The original
rx-8025 has been heavily rewritten anyway. Also, all the epson drivers
suffer from a lot of issues (some of those you already fixed) because
they are based on an old version of the driver.

> +/* Extension Register (1Dh) bit positions */
> +#define RX6110_BIT_EXT_TSEL		(7 << 0)
> +#define RX6110_BIT_EXT_WADA		(1 << 3)
> +#define RX6110_BIT_EXT_TE		(1 << 4)
> +#define RX6110_BIT_EXT_USEL		(1 << 5)
> +#define RX6110_BIT_EXT_FSEL		(3 << 6)
> +
> +/* Flag Register (1Eh) bit positions */
> +#define RX6110_BIT_FLAG_VLF		(1 << 1)
> +#define RX6110_BIT_FLAG_AF		(1 << 3)
> +#define RX6110_BIT_FLAG_TF		(1 << 4)
> +#define RX6110_BIT_FLAG_UF		(1 << 5)
> +
> +/* Control Register (1Fh) bit positions */
> +#define RX6110_BIT_CTRL_TSTP		(1 << 2)
> +#define RX6110_BIT_CTRL_AIE		(1 << 3)
> +#define RX6110_BIT_CTRL_TIE		(1 << 4)
> +#define RX6110_BIT_CTRL_UIE		(1 << 5)
> +#define RX6110_BIT_CTRL_STOP		(1 << 6)
> +#define RX6110_BIT_CTRL_TEST		(1 << 7)
> +

Can you use the BIT() macro?

> +static struct spi_driver rx6110_driver;
> +
> +struct rx6110_data {
> +	struct rtc_device *rtc;
> +	struct regmap *regmap;
> +	int ctrlreg;

ctrlreg is cached but never used.

> +};
> +
> +/**
> + * rx6110_get_week_day - translate reg_week_day to tm_wday
> + * @reg_week_day: weekday register value
> + *
> + * Return: an integer representing the tm_wday
> + */
> +static int rx6110_get_week_day(u8 reg_week_day)
> +{
> +	int tm_wday = -1;
> +	int i;
> +
> +	for (i = 0; i < 7; i++) {
> +		if (reg_week_day & 1) {
> +			tm_wday = i;
> +			break;
> +		}
> +		reg_week_day >>= 1;
> +	}
> +
> +	return tm_wday;
> +}

ffs() is probably better.

> +
> +/**
> + * rx6110_set_time - set the current time in the rx6110 registers
> + *
> + * @dev: the rtc device in use
> + * @tm: holds date and time
> + *
> + * BUG: The HW assumes every year that is a multiple of 4 to be a leap
> + * year. Next time this is wrong is 2100, which will not be a leap year
> + *
> + * Note: If STOP is not set/cleared, the clock will start when the seconds
> + *       register is written
> + *
> + */
> +static int rx6110_set_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct rx6110_data *rx6110 = dev_get_drvdata(dev);
> +	int ret;
> +
> +	if (tm->tm_year > 137)
> +		return -EINVAL;
> +

Seeing the comment comment above, this should probably be if
(tm->tm_year < 100 || tm->tm_year >= 200)
I don't think this particular part has any issue
handling 2038. However, on 32bit platform, your userspace is probably
not ready to handle those date. hwclock should return the correct date.

> + /* set STOP bit before changing clock/calendar */
> + ret = regmap_update_bits(rx6110->regmap, RX6110_REG_CTRL,
> +              RX6110_BIT_CTRL_STOP, RX6110_BIT_CTRL_STOP);
> + if (ret)
> +     return ret;
> +
> + ret = regmap_write(rx6110->regmap, RX6110_REG_SEC,
> +            bin2bcd(tm->tm_sec));
> + if (ret)
> +     return ret;
> + ret = regmap_write(rx6110->regmap, RX6110_REG_MIN,
> +            bin2bcd(tm->tm_min));
> + if (ret)
> +     return ret;
> + ret = regmap_write(rx6110->regmap, RX6110_REG_HOUR,
> +            bin2bcd(tm->tm_hour));
> + if (ret)
> +     return ret;
> +
> + ret = regmap_write(rx6110->regmap, RX6110_REG_MDAY,
> +            bin2bcd(tm->tm_mday));
> + if (ret)
> +     return ret;
> + ret = regmap_write(rx6110->regmap, RX6110_REG_MONTH,
> +            bin2bcd(tm->tm_mon + 1));
> + if (ret)
> +     return ret;
> + ret = regmap_write(rx6110->regmap, RX6110_REG_YEAR,
> +            bin2bcd(tm->tm_year % 100));
> + if (ret)
> +     return ret;
> + ret = regmap_write(rx6110->regmap, RX6110_REG_WDAY,
> +            1 << bin2bcd(tm->tm_wday));
> + if (ret)
> +     return ret;
> +

I feel that using a bulk write between setting and clearing the STOP bit
would be more efficient, in particular if one day we want to support
i2c.

> + /* clear STOP bit after changing clock/calendar */
> + ret = regmap_update_bits(rx6110->regmap, RX6110_REG_CTRL,
> +              RX6110_BIT_CTRL_STOP, 0);
> +
> + return ret;
> +}
> +/**
> + * rx6110_reset_time - reset the time to 1970/1/1 00:00
> + * @dev: the rtc device in use
> + * @tm: holds date and time
> + */
> +static int rx6110_reset_time(struct device *dev, struct rtc_time *tm)
> +{
> +	int ret;
> +
> +	tm->tm_sec = 0;
> +	tm->tm_min = 0;
> +	tm->tm_hour = 0;
> +	tm->tm_wday = 0;
> +	tm->tm_mday = 1;
> +	tm->tm_mon = 0;
> +	tm->tm_year = 70;
> +	ret = rx6110_set_time(dev, tm);
> +	if (ret) {
> +		dev_err(dev, "Failed to set time.\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}

This reset function is unnecessary.


> +
> +/**
> + * rx6110_get_time - get the current time from the rx6110 registers
> + * @dev: the rtc device in use
> + * @tm: holds date and time
> + */
> +static int rx6110_get_time(struct device *dev, struct rtc_time *tm)
> +{
> +	struct rx6110_data *rx6110 = dev_get_drvdata(dev);
> +	unsigned char date[7];
> +	int flags;
> +	int ret;
> +
> +	ret = regmap_read(rx6110->regmap, RX6110_REG_FLAG, &flags);
> +	if (ret)
> +		return -EINVAL;
> +
> +	/* check for VLF Flag (set at power-on) */
> +	if ((flags & RX6110_BIT_FLAG_VLF))
> +		return -EINVAL;
> +
> +	/* read registers to date */
> +	ret = regmap_bulk_read(rx6110->regmap, RX6110_REG_SEC, date, 7);
> +	if (ret)
> +		return ret;
> +
> +	tm->tm_sec = bcd2bin(date[0] & 0x7f);
> +	tm->tm_min = bcd2bin(date[1] & 0x7f);
> +	/* only 24-hour clock */
> +	tm->tm_hour = bcd2bin(date[2] & 0x3f);
> +	tm->tm_wday = rx6110_get_week_day(date[3] & 0x7f);
> +	tm->tm_mday = bcd2bin(date[4] & 0x3f);
> +	tm->tm_mon = bcd2bin(date[5] & 0x1f) - 1;
> +	tm->tm_year = bcd2bin(date[6]);
> +
> +	if (tm->tm_year < 70)
> +		tm->tm_year += 100;
> +

I think you are better off not playing with the date and only support
dates between 2000 and 2100. I don't really think anybody really care
about dates more than 15 years in the past.

> +	if (tm->tm_year > 137) {
> +		ret = rx6110_reset_time(dev, tm);
> +		if (ret)
> +			return ret;
> +	}

Please, never reset the date/time. This will confuse userspace. When
silently resetting the time, userspace as no way of knowing whether an error
really happened or you used a time machine ;). Return an error instead.

I think the check should be if (tm->tm_year > 200).

> +
> +	dev_dbg(dev, "%s: date %ds %dm %dh %dmd %dm %dy\n", __func__,
> +		tm->tm_sec, tm->tm_min, tm->tm_hour,
> +		tm->tm_mday, tm->tm_mon, tm->tm_year);
> +
> +	return rtc_valid_tm(tm);
> +}
> +
> +/**
> + * rx6110_init - initialize the rx6110 registers
> + *
> + * @rx6110: pointer to the rx6110 struct in use
> + *
> + */
> +static int rx6110_init(struct rx6110_data *rx6110)
> +{
> +	struct rtc_device *rtc = rx6110->rtc;
> +	int need_clear = 0;
> +	int need_reset = 0;
> +	int ext;
> +	int flags;
> +	int ctrl;
> +	int ret;
> +
> +	/* set reserved register 0x17 with specified value of 0xB8 */
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0xB8);
> +	if (ret)
> +		return ret;
> +
> +	/* set reserved register 0x30 with specified value of 0x00 */
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0x00);
> +	if (ret)
> +		return ret;
> +
> +	/* set reserved register 0x31 with specified value of 0x10 */
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0x10);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_IRQ, 0x0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_update_bits(rx6110->regmap, RX6110_REG_EXT,
> +				 RX6110_BIT_EXT_TE, 0);
> +	if (ret)
> +		return ret;
> +
> +	/* get current extension, flag, control register values */
> +	ret = regmap_read(rx6110->regmap, RX6110_REG_EXT, &ext);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_read(rx6110->regmap, RX6110_REG_FLAG, &flags);
> +	if (ret)
> +		return ret;
> +
> +	/* clear ctrl register */
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_CTRL, 0);
> +	if (ret)
> +		return ret;
> +
> +	ctrl = 0;
> +
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALMIN, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALHOUR, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALWDAY, 0);
> +	if (ret)
> +		return ret;
> +
> +	dev_dbg(&rtc->dev, "ext: %x, flag: %x, ctrl: %x\n", ext, flags, ctrl);
> +
> +	/* check for VLF Flag (set at power-on) */
> +	if ((flags & RX6110_BIT_FLAG_VLF)) {
> +		dev_warn(&rtc->dev, "Frequency stop was detected, probably due to a supply voltage drop\n");
> +		need_reset = 1;
> +		need_clear = 1;
> +	}

Again, never reset the time. The correct handling of that flag is to
return an error on read until the time is set again.you can check the
current rx8025 or rv8803 drivers, they handle the same logic. Maybe you
could also align the warnings message for missed alarms on those drivers.

> +
> +	/* check for Alarm Flag */
> +	if (flags & RX6110_BIT_FLAG_AF) {
> +		dev_warn(&rtc->dev, "Alarm was detected\n");
> +		need_clear = 1;
> +	}
> +
> +	/* check for Periodic Timer Flag */
> +	if (flags & RX6110_BIT_FLAG_TF) {
> +		dev_warn(&rtc->dev, "Periodic timer was detected\n");
> +		need_clear = 1;
> +	}
> +
> +	/* check for Update Timer Flag */
> +	if (flags & RX6110_BIT_FLAG_UF) {
> +		dev_warn(&rtc->dev, "Update timer was detected\n");
> +		need_clear = 1;
> +	}
> +
> +	/* reset or clear needed? */
> +	if (need_reset) {
> +		struct rtc_time tm;
> +
> +		/* clear ext register */
> +		ret = regmap_write(rx6110->regmap, RX6110_REG_EXT, 0);
> +		if (ret)
> +			return ret;
> +
> +		/* clear ctrl register */
> +		ret = regmap_write(rx6110->regmap, RX6110_REG_CTRL, 0);
> +		if (ret)
> +			return ret;
> +
> +		ctrl = 0;
> +
> +		ret = rx6110_reset_time(&rtc->dev, &tm);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	if (need_clear) {
> +		ret = regmap_write(rx6110->regmap, RX6110_REG_FLAG, 0);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	/* set "test bit" and reserved bits of control register zero */
> +	rx6110->ctrlreg = ctrl & ~RX6110_BIT_CTRL_TEST;
> +
> +	return 0;
> +}
> +
> +static struct rtc_class_ops rx6110_rtc_ops = {
> +	.read_time = rx6110_get_time,
> +	.set_time = rx6110_set_time,
> +};
> +
> +static struct regmap_config regmap_spi_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = RX6110_REG_IRQ,
> +	.read_flag_mask = 0x80,
> +};
> +
> +/**
> + * rx6110_probe - initialize rtc driver
> + * @spi: pointer to spi device
> + */
> +static int rx6110_probe(struct spi_device *spi)
> +{
> +	struct rx6110_data *rx6110;
> +	int err;
> +
> +	if ((spi->bits_per_word && spi->bits_per_word != 8)
> +	    || (spi->max_speed_hz > 2000000)
> +	    || (spi->mode != (SPI_CS_HIGH | SPI_CPOL | SPI_CPHA))) {
> +		dev_warn(&spi->dev, "SPI settings: bits_per_word: %d, max_speed_hz: %d, mode: %xh\n",
> +			spi->bits_per_word, spi->max_speed_hz, spi->mode);
> +		dev_warn(&spi->dev, "driving device in an unsupported mode");
> +	}
> +
> +	rx6110 = devm_kzalloc(&spi->dev, sizeof(*rx6110), GFP_KERNEL);
> +	if (!rx6110)
> +		return -ENOMEM;
> +
> +	rx6110->regmap = devm_regmap_init_spi(spi, &regmap_spi_config);
> +	if (IS_ERR(rx6110->regmap)) {
> +		dev_err(&spi->dev, "regmap init failed for rtc rx6110\n");
> +		return PTR_ERR(rx6110->regmap);
> +	}
> +
> +	spi_set_drvdata(spi, rx6110);
> +
> +	rx6110->rtc = devm_rtc_device_register(&spi->dev,
> +					       rx6110_driver.driver.name,
> +					       &rx6110_rtc_ops, THIS_MODULE);
> +
> +	if (IS_ERR(rx6110->rtc))
> +		return PTR_ERR(rx6110->rtc);
> +
> +	err = rx6110_init(rx6110);
> +	if (err)
> +		return err;
> +
> +	rx6110->rtc->max_user_freq = 1;
> +
> +	return 0;
> +}
> +
> +static int rx6110_remove(struct spi_device *spi)
> +{
> +	return 0;
> +}
> +
> +static const struct spi_device_id rx6110_id[] = {
> +	{ "rx6110", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(spi, rx6110_id);
> +
> +static struct spi_driver rx6110_driver = {
> +	.driver = {
> +		.name = "rx6110-rtc",
> +		.owner = THIS_MODULE,
> +	},
> +	.probe		= rx6110_probe,
> +	.remove		= rx6110_remove,
> +	.id_table	= rx6110_id,
> +};
> +
> +module_spi_driver(rx6110_driver);
> +
> +MODULE_AUTHOR("Val Krutov <val.krutov@erd.epson.com>");
> +MODULE_DESCRIPTION("RX-6110 SA RTC driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.6.2
>

Hello Alexandre,

Cc += Arnd

On Tue, Dec 01, 2015 at 03:42:18PM +0100, Alexandre Belloni wrote:
> > +/**
> > + * rx6110_set_time - set the current time in the rx6110 registers
> > + *
> > + * @dev: the rtc device in use
> > + * @tm: holds date and time
> > + *
> > + * BUG: The HW assumes every year that is a multiple of 4 to be a leap
> > + * year. Next time this is wrong is 2100, which will not be a leap year
> > + *
> > + * Note: If STOP is not set/cleared, the clock will start when the seconds
> > + *       register is written
> > + *
> > + */
> > +static int rx6110_set_time(struct device *dev, struct rtc_time *tm)
> > +{
> > +	struct rx6110_data *rx6110 = dev_get_drvdata(dev);
> > +	int ret;
> > +
> > +	if (tm->tm_year > 137)
> > +		return -EINVAL;
> > +
> 
> Seeing the comment comment above, this should probably be if
> (tm->tm_year < 100 || tm->tm_year >= 200)
> I don't think this particular part has any issue
> handling 2038. However, on 32bit platform, your userspace is probably
> not ready to handle those date. hwclock should return the correct date.

userspace is not ready because it cannot. Before this can be addressed,
quite some things need fixing first. If I understood correctly timerfd
for example is broken which completely locks up systemd.

Note this doesn't justify to not write a date later than 2037 in the rtc
driver however. Still thinking about how to handle this for the machines
we work on, we thought about letting the RTC_RD_TIME ioctl fail for
dates later than 2038 to work around this issue.

Best regards
Uwe

On 01/12/2015 at 20:49:19 +0100, Uwe Kleine-König wrote :
> > Seeing the comment comment above, this should probably be if
> > (tm->tm_year < 100 || tm->tm_year >= 200)
> > I don't think this particular part has any issue
> > handling 2038. However, on 32bit platform, your userspace is probably
> > not ready to handle those date. hwclock should return the correct date.
> 
> userspace is not ready because it cannot. Before this can be addressed,
> quite some things need fixing first. If I understood correctly timerfd
> for example is broken which completely locks up systemd.
> 
> Note this doesn't justify to not write a date later than 2037 in the rtc
> driver however. Still thinking about how to handle this for the machines
> we work on, we thought about letting the RTC_RD_TIME ioctl fail for
> dates later than 2038 to work around this issue.
> 

Yeah but the rtc doesn't have any issue handling dates after 2038 so if
it is used on a 64bit system, it can work properly until february 2100.

Also, I'm not sure how that solves your problem anyway.

Hi!

On Tue, Dec 01, 2015 at 03:42:18PM +0100, Alexandre Belloni wrote:
> Hi,
> 
> Thanks for that patch, I'm sorry I didn't find the time to reply to your
> previous version.
> 

No problem.

> On 01/12/2015 at 14:48:20 +0100, Steffen Trumtrar wrote :
> > diff --git a/drivers/rtc/rtc-rx6110.c b/drivers/rtc/rtc-rx6110.c
> > new file mode 100644
> > index 000000000000..7a828adf9794
> > --- /dev/null
> > +++ b/drivers/rtc/rtc-rx6110.c
> > @@ -0,0 +1,480 @@
> > +/*
> > + * Driver for the Epson RTC module RX-6110 SA
> > + *
> > + * Copyright(C) 2015 Pengutronix, Steffen Trumtrar <kernel@pengutronix.de>
> > + * Copyright(C) SEIKO EPSON CORPORATION 2013. All rights reserved.
> > + *
> > + * Derived from RX-8025 driver:
> > + * Copyright (C) 2009 Wolfgang Grandegger <wg@grandegger.com>
> > + *
> > + * Copyright (C) 2005 by Digi International Inc.
> > + * All rights reserved.
> > + *
> > + * Modified by fengjh at rising.com.cn
> > + * <http://lists.lm-sensors.org/mailman/listinfo/lm-sensors>
> > + * 2006.11
> > + *
> > + * Code cleanup by Sergei Poselenov, <sposelenov@emcraft.com>
> > + * Converted to new style by Wolfgang Grandegger <wg@grandegger.com>
> > + * Alarm and periodic interrupt added by Dmitry Rakhchev <rda@emcraft.com>
> > + *
> > + *
> 
> Please remove all those unnecessary copyrights and credits. The original
> rx-8025 has been heavily rewritten anyway. Also, all the epson drivers
> suffer from a lot of issues (some of those you already fixed) because
> they are based on an old version of the driver.
> 

Okay. I wasn't sure how okay it is to just get rid of it.
I removed everything after the SEIKO EPSON copyright.

> > +/* Extension Register (1Dh) bit positions */
> > +#define RX6110_BIT_EXT_TSEL		(7 << 0)
> > +#define RX6110_BIT_EXT_WADA		(1 << 3)
> > +#define RX6110_BIT_EXT_TE		(1 << 4)
> > +#define RX6110_BIT_EXT_USEL		(1 << 5)
> > +#define RX6110_BIT_EXT_FSEL		(3 << 6)
> > +
> > +/* Flag Register (1Eh) bit positions */
> > +#define RX6110_BIT_FLAG_VLF		(1 << 1)
> > +#define RX6110_BIT_FLAG_AF		(1 << 3)
> > +#define RX6110_BIT_FLAG_TF		(1 << 4)
> > +#define RX6110_BIT_FLAG_UF		(1 << 5)
> > +
> > +/* Control Register (1Fh) bit positions */
> > +#define RX6110_BIT_CTRL_TSTP		(1 << 2)
> > +#define RX6110_BIT_CTRL_AIE		(1 << 3)
> > +#define RX6110_BIT_CTRL_TIE		(1 << 4)
> > +#define RX6110_BIT_CTRL_UIE		(1 << 5)
> > +#define RX6110_BIT_CTRL_STOP		(1 << 6)
> > +#define RX6110_BIT_CTRL_TEST		(1 << 7)
> > +
> 
> Can you use the BIT() macro?
> 
> > +static struct spi_driver rx6110_driver;
> > +
> > +struct rx6110_data {
> > +	struct rtc_device *rtc;
> > +	struct regmap *regmap;
> > +	int ctrlreg;
> 
> ctrlreg is cached but never used.
> 
> > +};
> > +
> > +/**
> > + * rx6110_get_week_day - translate reg_week_day to tm_wday
> > + * @reg_week_day: weekday register value
> > + *
> > + * Return: an integer representing the tm_wday
> > + */
> > +static int rx6110_get_week_day(u8 reg_week_day)
> > +{
> > +	int tm_wday = -1;
> > +	int i;
> > +
> > +	for (i = 0; i < 7; i++) {
> > +		if (reg_week_day & 1) {
> > +			tm_wday = i;
> > +			break;
> > +		}
> > +		reg_week_day >>= 1;
> > +	}
> > +
> > +	return tm_wday;
> > +}
> 
> ffs() is probably better.
> 
> > +
> > +/**
> > + * rx6110_set_time - set the current time in the rx6110 registers
> > + *
> > + * @dev: the rtc device in use
> > + * @tm: holds date and time
> > + *
> > + * BUG: The HW assumes every year that is a multiple of 4 to be a leap
> > + * year. Next time this is wrong is 2100, which will not be a leap year
> > + *
> > + * Note: If STOP is not set/cleared, the clock will start when the seconds
> > + *       register is written
> > + *
> > + */
> > +static int rx6110_set_time(struct device *dev, struct rtc_time *tm)
> > +{
> > +	struct rx6110_data *rx6110 = dev_get_drvdata(dev);
> > +	int ret;
> > +
> > +	if (tm->tm_year > 137)
> > +		return -EINVAL;
> > +
> 
> Seeing the comment comment above, this should probably be if
> (tm->tm_year < 100 || tm->tm_year >= 200)
> I don't think this particular part has any issue
> handling 2038. However, on 32bit platform, your userspace is probably
> not ready to handle those date. hwclock should return the correct date.
> 
> > + /* set STOP bit before changing clock/calendar */
> > + ret = regmap_update_bits(rx6110->regmap, RX6110_REG_CTRL,
> > +              RX6110_BIT_CTRL_STOP, RX6110_BIT_CTRL_STOP);
> > + if (ret)
> > +     return ret;
> > +
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_SEC,
> > +            bin2bcd(tm->tm_sec));
> > + if (ret)
> > +     return ret;
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_MIN,
> > +            bin2bcd(tm->tm_min));
> > + if (ret)
> > +     return ret;
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_HOUR,
> > +            bin2bcd(tm->tm_hour));
> > + if (ret)
> > +     return ret;
> > +
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_MDAY,
> > +            bin2bcd(tm->tm_mday));
> > + if (ret)
> > +     return ret;
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_MONTH,
> > +            bin2bcd(tm->tm_mon + 1));
> > + if (ret)
> > +     return ret;
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_YEAR,
> > +            bin2bcd(tm->tm_year % 100));
> > + if (ret)
> > +     return ret;
> > + ret = regmap_write(rx6110->regmap, RX6110_REG_WDAY,
> > +            1 << bin2bcd(tm->tm_wday));
> > + if (ret)
> > +     return ret;
> > +
> 
> I feel that using a bulk write between setting and clearing the STOP bit
> would be more efficient, in particular if one day we want to support
> i2c.
> 
> > + /* clear STOP bit after changing clock/calendar */
> > + ret = regmap_update_bits(rx6110->regmap, RX6110_REG_CTRL,
> > +              RX6110_BIT_CTRL_STOP, 0);
> > +
> > + return ret;
> > +}
> > +/**
> > + * rx6110_reset_time - reset the time to 1970/1/1 00:00
> > + * @dev: the rtc device in use
> > + * @tm: holds date and time
> > + */
> > +static int rx6110_reset_time(struct device *dev, struct rtc_time *tm)
> > +{
> > +	int ret;
> > +
> > +	tm->tm_sec = 0;
> > +	tm->tm_min = 0;
> > +	tm->tm_hour = 0;
> > +	tm->tm_wday = 0;
> > +	tm->tm_mday = 1;
> > +	tm->tm_mon = 0;
> > +	tm->tm_year = 70;
> > +	ret = rx6110_set_time(dev, tm);
> > +	if (ret) {
> > +		dev_err(dev, "Failed to set time.\n");
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> This reset function is unnecessary.
> 
> 
> > +
> > +/**
> > + * rx6110_get_time - get the current time from the rx6110 registers
> > + * @dev: the rtc device in use
> > + * @tm: holds date and time
> > + */
> > +static int rx6110_get_time(struct device *dev, struct rtc_time *tm)
> > +{
> > +	struct rx6110_data *rx6110 = dev_get_drvdata(dev);
> > +	unsigned char date[7];
> > +	int flags;
> > +	int ret;
> > +
> > +	ret = regmap_read(rx6110->regmap, RX6110_REG_FLAG, &flags);
> > +	if (ret)
> > +		return -EINVAL;
> > +
> > +	/* check for VLF Flag (set at power-on) */
> > +	if ((flags & RX6110_BIT_FLAG_VLF))
> > +		return -EINVAL;
> > +
> > +	/* read registers to date */
> > +	ret = regmap_bulk_read(rx6110->regmap, RX6110_REG_SEC, date, 7);
> > +	if (ret)
> > +		return ret;
> > +
> > +	tm->tm_sec = bcd2bin(date[0] & 0x7f);
> > +	tm->tm_min = bcd2bin(date[1] & 0x7f);
> > +	/* only 24-hour clock */
> > +	tm->tm_hour = bcd2bin(date[2] & 0x3f);
> > +	tm->tm_wday = rx6110_get_week_day(date[3] & 0x7f);
> > +	tm->tm_mday = bcd2bin(date[4] & 0x3f);
> > +	tm->tm_mon = bcd2bin(date[5] & 0x1f) - 1;
> > +	tm->tm_year = bcd2bin(date[6]);
> > +
> > +	if (tm->tm_year < 70)
> > +		tm->tm_year += 100;
> > +
> 
> I think you are better off not playing with the date and only support
> dates between 2000 and 2100. I don't really think anybody really care
> about dates more than 15 years in the past.
> 
> > +	if (tm->tm_year > 137) {
> > +		ret = rx6110_reset_time(dev, tm);
> > +		if (ret)
> > +			return ret;
> > +	}
> 
> Please, never reset the date/time. This will confuse userspace. When
> silently resetting the time, userspace as no way of knowing whether an error
> really happened or you used a time machine ;). Return an error instead.
> 
> I think the check should be if (tm->tm_year > 200).
> 
> > +
> > +	dev_dbg(dev, "%s: date %ds %dm %dh %dmd %dm %dy\n", __func__,
> > +		tm->tm_sec, tm->tm_min, tm->tm_hour,
> > +		tm->tm_mday, tm->tm_mon, tm->tm_year);
> > +
> > +	return rtc_valid_tm(tm);
> > +}
> > +
> > +/**
> > + * rx6110_init - initialize the rx6110 registers
> > + *
> > + * @rx6110: pointer to the rx6110 struct in use
> > + *
> > + */
> > +static int rx6110_init(struct rx6110_data *rx6110)
> > +{
> > +	struct rtc_device *rtc = rx6110->rtc;
> > +	int need_clear = 0;
> > +	int need_reset = 0;
> > +	int ext;
> > +	int flags;
> > +	int ctrl;
> > +	int ret;
> > +
> > +	/* set reserved register 0x17 with specified value of 0xB8 */
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0xB8);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* set reserved register 0x30 with specified value of 0x00 */
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0x00);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* set reserved register 0x31 with specified value of 0x10 */
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_RES1, 0x10);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_IRQ, 0x0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_update_bits(rx6110->regmap, RX6110_REG_EXT,
> > +				 RX6110_BIT_EXT_TE, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* get current extension, flag, control register values */
> > +	ret = regmap_read(rx6110->regmap, RX6110_REG_EXT, &ext);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_read(rx6110->regmap, RX6110_REG_FLAG, &flags);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* clear ctrl register */
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_CTRL, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ctrl = 0;
> > +
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALMIN, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALHOUR, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = regmap_write(rx6110->regmap, RX6110_REG_ALWDAY, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	dev_dbg(&rtc->dev, "ext: %x, flag: %x, ctrl: %x\n", ext, flags, ctrl);
> > +
> > +	/* check for VLF Flag (set at power-on) */
> > +	if ((flags & RX6110_BIT_FLAG_VLF)) {
> > +		dev_warn(&rtc->dev, "Frequency stop was detected, probably due to a supply voltage drop\n");
> > +		need_reset = 1;
> > +		need_clear = 1;
> > +	}
> 
> Again, never reset the time. The correct handling of that flag is to
> return an error on read until the time is set again.you can check the
> current rx8025 or rv8803 drivers, they handle the same logic. Maybe you
> could also align the warnings message for missed alarms on those drivers.
> 

(...)

To make it short: I have done everything of the above :-)

Thanks,
Steffen Trumtrar