rtc: rv3028: add new driver

Add a driver for the MicroCrystal RV-3028. It is a SMT Real-Time Clock
Module that incorporates an integrated CMOS circuit together with an XTAL.
It has an i2c interface.

The driver handles date/time, alarms, trickle charging, timestamping,
frequency offset correction, EEPROM and NVRAM.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

4 files changed, 743 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/rtc/rtc.txt b/Documentation/devicetree/bindings/rtc/rtc.txt
index d86e2850fe1c..3e6a215e7304 100644
--- a/Documentation/devicetree/bindings/rtc/rtc.txt
+++ b/Documentation/devicetree/bindings/rtc/rtc.txt
@@ -52,6 +52,7 @@ emmicro,em3027		EM Microelectronic EM3027 Real-time Clock
 isil,isl1208		Intersil ISL1208 Low Power RTC with Battery Backed SRAM
 isil,isl1218		Intersil ISL1218 Low Power RTC with Battery Backed SRAM
 isil,isl12022		Intersil ISL12022 Real-time Clock
+microcrystal,rv3028	Real Time Clock Module with I2C-Bus
 microcrystal,rv3029	Real Time Clock Module with I2C-Bus
 microcrystal,rv8523	Real Time Clock
 nxp,pcf2127		Real-time clock
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 7d61bb382cf3..a08785ac8903 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -626,6 +626,15 @@ config RTC_DRV_EM3027
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-em3027.
 
+config RTC_DRV_RV3028
+	tristate "Micro Crystal RV3028"
+	help
+	  If you say yes here you get support for the Micro Crystal
+	  RV3028.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-rv3028.
+
 config RTC_DRV_RV8803
 	tristate "Micro Crystal RV8803, Epson RX8900"
 	help
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index b994323942bd..6dc1e561f533 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -139,6 +139,7 @@ obj-$(CONFIG_RTC_DRV_RS5C313)	+= rtc-rs5c313.o
 obj-$(CONFIG_RTC_DRV_RS5C348)	+= rtc-rs5c348.o
 obj-$(CONFIG_RTC_DRV_RS5C372)	+= rtc-rs5c372.o
 obj-$(CONFIG_RTC_DRV_RTD119X)	+= rtc-rtd119x.o
+obj-$(CONFIG_RTC_DRV_RV3028)	+= rtc-rv3028.o
 obj-$(CONFIG_RTC_DRV_RV3029C2)	+= rtc-rv3029c2.o
 obj-$(CONFIG_RTC_DRV_RV8803)	+= rtc-rv8803.o
 obj-$(CONFIG_RTC_DRV_RX4581)	+= rtc-rx4581.o
diff --git a/drivers/rtc/rtc-rv3028.c b/drivers/rtc/rtc-rv3028.c
new file mode 100644
index 000000000000..06884ebb7a61
--- /dev/null
+++ b/drivers/rtc/rtc-rv3028.c
@@ -0,0 +1,732 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * RTC driver for the Micro Crystal RV3028
+ *
+ * Copyright (C) 2019 Micro Crystal SA
+ *
+ * Alexandre Belloni <alexandre.belloni@bootlin.com>
+ *
+ */
+
+#include <linux/bcd.h>
+#include <linux/bitops.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/log2.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+
+#define RV3028_SEC			0x00
+#define RV3028_MIN			0x01
+#define RV3028_HOUR			0x02
+#define RV3028_WDAY			0x03
+#define RV3028_DAY			0x04
+#define RV3028_MONTH			0x05
+#define RV3028_YEAR			0x06
+#define RV3028_ALARM_MIN		0x07
+#define RV3028_ALARM_HOUR		0x08
+#define RV3028_ALARM_DAY		0x09
+#define RV3028_STATUS			0x0E
+#define RV3028_CTRL1			0x0F
+#define RV3028_CTRL2			0x10
+#define RV3028_EVT_CTRL			0x13
+#define RV3028_TS_COUNT			0x14
+#define RV3028_TS_SEC			0x15
+#define RV3028_RAM1			0x1F
+#define RV3028_EEPROM_ADDR		0x25
+#define RV3028_EEPROM_DATA		0x26
+#define RV3028_EEPROM_CMD		0x27
+#define RV3028_CLKOUT			0x35
+#define RV3028_OFFSET			0x36
+#define RV3028_BACKUP			0x37
+
+#define RV3028_STATUS_PORF		BIT(0)
+#define RV3028_STATUS_EVF		BIT(1)
+#define RV3028_STATUS_AF		BIT(2)
+#define RV3028_STATUS_TF		BIT(3)
+#define RV3028_STATUS_UF		BIT(4)
+#define RV3028_STATUS_BSF		BIT(5)
+#define RV3028_STATUS_CLKF		BIT(6)
+#define RV3028_STATUS_EEBUSY		BIT(7)
+
+#define RV3028_CTRL1_EERD		BIT(3)
+#define RV3028_CTRL1_WADA		BIT(5)
+
+#define RV3028_CTRL2_RESET		BIT(0)
+#define RV3028_CTRL2_12_24		BIT(1)
+#define RV3028_CTRL2_EIE		BIT(2)
+#define RV3028_CTRL2_AIE		BIT(3)
+#define RV3028_CTRL2_TIE		BIT(4)
+#define RV3028_CTRL2_UIE		BIT(5)
+#define RV3028_CTRL2_TSE		BIT(7)
+
+#define RV3028_EVT_CTRL_TSR		BIT(2)
+
+#define RV3028_EEPROM_CMD_WRITE		0x21
+#define RV3028_EEPROM_CMD_READ		0x22
+
+#define RV3028_EEBUSY_POLL		10000
+#define RV3028_EEBUSY_TIMEOUT		100000
+
+#define RV3028_BACKUP_TCE		BIT(5)
+#define RV3028_BACKUP_TCR_MASK		GENMASK(1,0)
+
+#define OFFSET_STEP_PPT			953674
+
+enum rv3028_type {
+	rv_3028,
+};
+
+struct rv3028_data {
+	struct regmap *regmap;
+	struct rtc_device *rtc;
+	enum rv3028_type type;
+};
+
+static u16 rv3028_trickle_resistors[] = {1000, 3000, 6000, 11000};
+
+static ssize_t timestamp0_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev->parent);
+
+	regmap_update_bits(rv3028->regmap, RV3028_EVT_CTRL, RV3028_EVT_CTRL_TSR,
+			   RV3028_EVT_CTRL_TSR);
+
+	return count;
+};
+
+static ssize_t timestamp0_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev->parent);
+	struct rtc_time tm;
+	int ret, count;
+	u8 date[6];
+
+	ret = regmap_read(rv3028->regmap, RV3028_TS_COUNT, &count);
+	if (ret)
+		return ret;
+
+	if (!count)
+		return 0;
+
+	ret = regmap_bulk_read(rv3028->regmap, RV3028_TS_SEC, date,
+			       sizeof(date));
+	if (ret)
+		return ret;
+
+	tm.tm_sec = bcd2bin(date[0]);
+	tm.tm_min = bcd2bin(date[1]);
+	tm.tm_hour = bcd2bin(date[2]);
+	tm.tm_mday = bcd2bin(date[3]);
+	tm.tm_mon = bcd2bin(date[4]) - 1;
+	tm.tm_year = bcd2bin(date[5]) + 100;
+
+	ret = rtc_valid_tm(&tm);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)rtc_tm_to_time64(&tm));
+};
+
+static DEVICE_ATTR_RW(timestamp0);
+
+static ssize_t timestamp0_count_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev->parent);
+	int ret, count;
+
+	ret = regmap_read(rv3028->regmap, RV3028_TS_COUNT, &count);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%u\n", count);
+};
+
+static DEVICE_ATTR_RO(timestamp0_count);
+
+static struct attribute *rv3028_attrs[] = {
+	&dev_attr_timestamp0.attr,
+	&dev_attr_timestamp0_count.attr,
+	NULL
+};
+
+static const struct attribute_group rv3028_attr_group = {
+	.attrs	= rv3028_attrs,
+};
+
+static irqreturn_t rv3028_handle_irq(int irq, void *dev_id)
+{
+	struct rv3028_data *rv3028 = dev_id;
+	unsigned long events = 0;
+	u32 status = 0, ctrl = 0;
+
+	if (regmap_read(rv3028->regmap, RV3028_STATUS, &status) < 0 ||
+	   status == 0) {
+		return IRQ_NONE;
+	}
+
+	if (status & RV3028_STATUS_PORF)
+		dev_warn(&rv3028->rtc->dev, "Voltage low, data loss detected.\n");
+
+	if (status & RV3028_STATUS_TF) {
+		status |= RV3028_STATUS_TF;
+		ctrl |= RV3028_CTRL2_TIE;
+		events |= RTC_PF;
+	}
+
+	if (status & RV3028_STATUS_AF) {
+		status |= RV3028_STATUS_AF;
+		ctrl |= RV3028_CTRL2_AIE;
+		events |= RTC_AF;
+	}
+
+	if (status & RV3028_STATUS_UF) {
+		status |= RV3028_STATUS_UF;
+		ctrl |= RV3028_CTRL2_UIE;
+		events |= RTC_UF;
+	}
+
+	if (events) {
+		rtc_update_irq(rv3028->rtc, 1, events);
+		regmap_update_bits(rv3028->regmap, RV3028_STATUS, status, 0);
+		regmap_update_bits(rv3028->regmap, RV3028_CTRL2, ctrl, 0);
+	}
+
+	if (status & RV3028_STATUS_EVF) {
+		sysfs_notify(&rv3028->rtc->dev.kobj, NULL,
+			     dev_attr_timestamp0.attr.name);
+		dev_warn(&rv3028->rtc->dev, "event detected");
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int rv3028_get_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	u8 date[7];
+	int ret, status;
+
+	ret = regmap_read(rv3028->regmap, RV3028_STATUS, &status);
+	if (ret < 0)
+		return ret;
+
+	if (status & RV3028_STATUS_PORF) {
+		dev_warn(dev, "Voltage low, data is invalid.\n");
+		return -EINVAL;
+	}
+
+	ret = regmap_bulk_read(rv3028->regmap, RV3028_SEC, date, sizeof(date));
+	if (ret)
+		return ret;
+
+	tm->tm_sec  = bcd2bin(date[RV3028_SEC] & 0x7f);
+	tm->tm_min  = bcd2bin(date[RV3028_MIN] & 0x7f);
+	tm->tm_hour = bcd2bin(date[RV3028_HOUR] & 0x3f);
+	tm->tm_wday = ilog2(date[RV3028_WDAY] & 0x7f);
+	tm->tm_mday = bcd2bin(date[RV3028_DAY] & 0x3f);
+	tm->tm_mon  = bcd2bin(date[RV3028_MONTH] & 0x1f) - 1;
+	tm->tm_year = bcd2bin(date[RV3028_YEAR]) + 100;
+
+	return 0;
+}
+
+static int rv3028_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	u8 date[7];
+	int ret;
+
+	date[RV3028_SEC]   = bin2bcd(tm->tm_sec);
+	date[RV3028_MIN]   = bin2bcd(tm->tm_min);
+	date[RV3028_HOUR]  = bin2bcd(tm->tm_hour);
+	date[RV3028_WDAY]  = 1 << (tm->tm_wday);
+	date[RV3028_DAY]   = bin2bcd(tm->tm_mday);
+	date[RV3028_MONTH] = bin2bcd(tm->tm_mon + 1);
+	date[RV3028_YEAR]  = bin2bcd(tm->tm_year - 100);
+
+	/*
+	 * Writing to the Seconds register has the same effect as setting RESET
+	 * bit to 1
+	 */
+	ret = regmap_bulk_write(rv3028->regmap, RV3028_SEC, date,
+				sizeof(date));
+	if (ret)
+		return ret;
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_STATUS,
+				 RV3028_STATUS_PORF, 0);
+
+	return ret;
+}
+
+static int rv3028_get_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	u8 alarmvals[3];
+	int status, ctrl, ret;
+
+	ret = regmap_bulk_read(rv3028->regmap, RV3028_ALARM_MIN, alarmvals,
+			       sizeof(alarmvals));
+	if (ret)
+		return ret;
+
+	ret = regmap_read(rv3028->regmap, RV3028_STATUS, &status);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_read(rv3028->regmap, RV3028_CTRL2, &ctrl);
+	if (ret < 0)
+		return ret;
+
+	alrm->time.tm_sec  = 0;
+	alrm->time.tm_min  = bcd2bin(alarmvals[0] & 0x7f);
+	alrm->time.tm_hour = bcd2bin(alarmvals[1] & 0x3f);
+	alrm->time.tm_mday = bcd2bin(alarmvals[2] & 0x3f);
+
+	alrm->enabled = !!(ctrl & RV3028_CTRL2_AIE);
+	alrm->pending = (status & RV3028_STATUS_AF) && alrm->enabled;
+
+	return 0;
+}
+
+static int rv3028_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	u8 alarmvals[3];
+	u8 ctrl = 0;
+	int ret;
+
+	/* The alarm has no seconds, round up to nearest minute */
+	if (alrm->time.tm_sec) {
+		time64_t alarm_time = rtc_tm_to_time64(&alrm->time);
+
+		alarm_time += 60 - alrm->time.tm_sec;
+		rtc_time64_to_tm(alarm_time, &alrm->time);
+	}
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_CTRL2,
+				 RV3028_CTRL2_AIE | RV3028_CTRL2_UIE, 0);
+	if (ret)
+		return ret;
+
+	alarmvals[0] = bin2bcd(alrm->time.tm_min);
+	alarmvals[1] = bin2bcd(alrm->time.tm_hour);
+	alarmvals[2] = bin2bcd(alrm->time.tm_mday);
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_STATUS,
+				 RV3028_STATUS_AF, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_bulk_write(rv3028->regmap, RV3028_ALARM_MIN, alarmvals,
+				sizeof(alarmvals));
+	if (ret)
+		return ret;
+
+	if (alrm->enabled) {
+		if (rv3028->rtc->uie_rtctimer.enabled)
+			ctrl |= RV3028_CTRL2_UIE;
+		if (rv3028->rtc->aie_timer.enabled)
+			ctrl |= RV3028_CTRL2_AIE;
+	}
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_CTRL2,
+				 RV3028_CTRL2_UIE | RV3028_CTRL2_AIE, ctrl);
+
+	return ret;
+}
+
+static int rv3028_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	int ctrl = 0, ret;
+
+	if (enabled) {
+		if (rv3028->rtc->uie_rtctimer.enabled)
+			ctrl |= RV3028_CTRL2_UIE;
+		if (rv3028->rtc->aie_timer.enabled)
+			ctrl |= RV3028_CTRL2_AIE;
+	}
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_STATUS,
+				 RV3028_STATUS_AF | RV3028_STATUS_UF, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_CTRL2,
+				 RV3028_CTRL2_UIE | RV3028_CTRL2_AIE, ctrl);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int rv3028_read_offset(struct device *dev, long *offset)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	int ret, value, steps;
+
+	ret = regmap_read(rv3028->regmap, RV3028_OFFSET, &value);
+	if (ret < 0)
+		return ret;
+
+	steps = sign_extend32(value << 1, 8);
+
+	ret = regmap_read(rv3028->regmap, RV3028_BACKUP, &value);
+	if (ret < 0)
+		return ret;
+
+	steps += value >> 7;
+
+	*offset = DIV_ROUND_CLOSEST(steps * OFFSET_STEP_PPT, 1000);
+
+	return 0;
+}
+
+static int rv3028_set_offset(struct device *dev, long offset)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	int ret;
+
+	offset = clamp(offset, -244141L, 243187L) * 1000;
+	offset = DIV_ROUND_CLOSEST(offset, OFFSET_STEP_PPT);
+
+	ret = regmap_write(rv3028->regmap, RV3028_OFFSET, offset >> 1);
+	if (ret < 0)
+		return ret;
+
+	return regmap_update_bits(rv3028->regmap, RV3028_BACKUP, BIT(7),
+				  offset << 7);
+}
+
+static int rv3028_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+	struct rv3028_data *rv3028 = dev_get_drvdata(dev);
+	int status, ret = 0;
+
+	switch (cmd) {
+	case RTC_VL_READ:
+		ret = regmap_read(rv3028->regmap, RV3028_STATUS, &status);
+		if (ret < 0)
+			return ret;
+
+		if (status & RV3028_STATUS_PORF)
+			dev_warn(&rv3028->rtc->dev, "Voltage low, data loss detected.\n");
+
+		status &= RV3028_STATUS_PORF;
+
+		if (copy_to_user((void __user *)arg, &status, sizeof(int)))
+			return -EFAULT;
+
+		return 0;
+
+	case RTC_VL_CLR:
+		ret = regmap_update_bits(rv3028->regmap, RV3028_STATUS,
+					 RV3028_STATUS_PORF, 0);
+
+		return ret;
+
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+
+static int rv3028_nvram_write(void *priv, unsigned int offset, void *val,
+			      size_t bytes)
+{
+	return regmap_bulk_write(priv, RV3028_RAM1 + offset, val, bytes);
+}
+
+static int rv3028_nvram_read(void *priv, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	return regmap_bulk_read(priv, RV3028_RAM1 + offset, val, bytes);
+}
+
+static int rv3028_eeprom_write(void *priv, unsigned int offset, void *val,
+			       size_t bytes)
+{
+	u32 status, ctrl1;
+	int i, ret, err;
+	u8 *buf = val;
+
+	ret = regmap_read(priv, RV3028_CTRL1, &ctrl1);
+	if (ret)
+		return ret;
+
+	if (!(ctrl1 & RV3028_CTRL1_EERD)) {
+		ret = regmap_update_bits(priv, RV3028_CTRL1,
+					 RV3028_CTRL1_EERD, RV3028_CTRL1_EERD);
+		if (ret)
+			return ret;
+
+		ret = regmap_read_poll_timeout(priv, RV3028_STATUS, status,
+					       !(status & RV3028_STATUS_EEBUSY),
+					       RV3028_EEBUSY_POLL,
+					       RV3028_EEBUSY_TIMEOUT);
+		if (ret)
+			goto restore_eerd;
+	}
+
+	for (i = 0; i < bytes; i++) {
+		ret = regmap_write(priv, RV3028_EEPROM_ADDR, offset + i);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_write(priv, RV3028_EEPROM_DATA, buf[i]);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_write(priv, RV3028_EEPROM_CMD, 0x0);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_write(priv, RV3028_EEPROM_CMD,
+				   RV3028_EEPROM_CMD_WRITE);
+		if (ret)
+			goto restore_eerd;
+
+		usleep_range(RV3028_EEBUSY_POLL, RV3028_EEBUSY_TIMEOUT);
+
+		ret = regmap_read_poll_timeout(priv, RV3028_STATUS, status,
+					       !(status & RV3028_STATUS_EEBUSY),
+					       RV3028_EEBUSY_POLL,
+					       RV3028_EEBUSY_TIMEOUT);
+		if (ret)
+			goto restore_eerd;
+	}
+
+restore_eerd:
+	if (!(ctrl1 & RV3028_CTRL1_EERD))
+	{
+		err = regmap_update_bits(priv, RV3028_CTRL1, RV3028_CTRL1_EERD,
+					 0);
+		if (err && !ret)
+			ret = err;
+	}
+
+	return ret;
+}
+
+static int rv3028_eeprom_read(void *priv, unsigned int offset, void *val,
+			      size_t bytes)
+{
+	u32 status, ctrl1, data;
+	int i, ret, err;
+	u8 *buf = val;
+
+	ret = regmap_read(priv, RV3028_CTRL1, &ctrl1);
+	if (ret)
+		return ret;
+
+	if (!(ctrl1 & RV3028_CTRL1_EERD)) {
+		ret = regmap_update_bits(priv, RV3028_CTRL1,
+					 RV3028_CTRL1_EERD, RV3028_CTRL1_EERD);
+		if (ret)
+			return ret;
+
+		ret = regmap_read_poll_timeout(priv, RV3028_STATUS, status,
+					       !(status & RV3028_STATUS_EEBUSY),
+					       RV3028_EEBUSY_POLL,
+					       RV3028_EEBUSY_TIMEOUT);
+		if (ret)
+			goto restore_eerd;
+	}
+
+	for (i = 0; i < bytes; i++) {
+		ret = regmap_write(priv, RV3028_EEPROM_ADDR, offset + i);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_write(priv, RV3028_EEPROM_CMD, 0x0);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_write(priv, RV3028_EEPROM_CMD,
+				   RV3028_EEPROM_CMD_READ);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_read_poll_timeout(priv, RV3028_STATUS, status,
+					       !(status & RV3028_STATUS_EEBUSY),
+					       RV3028_EEBUSY_POLL,
+					       RV3028_EEBUSY_TIMEOUT);
+		if (ret)
+			goto restore_eerd;
+
+		ret = regmap_read(priv, RV3028_EEPROM_DATA, &data);
+		if (ret)
+			goto restore_eerd;
+		buf[i] = data;
+	}
+
+restore_eerd:
+	if (!(ctrl1 & RV3028_CTRL1_EERD))
+	{
+		err = regmap_update_bits(priv, RV3028_CTRL1, RV3028_CTRL1_EERD,
+					 0);
+		if (err && !ret)
+			ret = err;
+	}
+
+	return ret;
+}
+
+static struct rtc_class_ops rv3028_rtc_ops = {
+	.read_time = rv3028_get_time,
+	.set_time = rv3028_set_time,
+	.read_offset = rv3028_read_offset,
+	.set_offset = rv3028_set_offset,
+	.ioctl = rv3028_ioctl,
+};
+
+static const struct regmap_config regmap_config = {
+        .reg_bits = 8,
+        .val_bits = 8,
+        .max_register = 0x37,
+};
+
+static int rv3028_probe(struct i2c_client *client)
+{
+	struct rv3028_data *rv3028;
+	int ret, status;
+	u32 ohms;
+	struct nvmem_config nvmem_cfg = {
+		.name = "rv3028_nvram",
+		.word_size = 1,
+		.stride = 1,
+		.size = 2,
+		.type = NVMEM_TYPE_BATTERY_BACKED,
+		.reg_read = rv3028_nvram_read,
+		.reg_write = rv3028_nvram_write,
+	};
+	struct nvmem_config eeprom_cfg = {
+		.name = "rv3028_eeprom",
+		.word_size = 1,
+		.stride = 1,
+		.size = 43,
+		.type = NVMEM_TYPE_EEPROM,
+		.reg_read = rv3028_eeprom_read,
+		.reg_write = rv3028_eeprom_write,
+	};
+
+	rv3028 = devm_kzalloc(&client->dev, sizeof(struct rv3028_data),
+			      GFP_KERNEL);
+	if (!rv3028)
+		return -ENOMEM;
+
+	rv3028->regmap = devm_regmap_init_i2c(client, &regmap_config);
+
+	i2c_set_clientdata(client, rv3028);
+
+	ret = regmap_read(rv3028->regmap, RV3028_STATUS, &status);
+	if (ret < 0)
+		return ret;
+
+	if (status & RV3028_STATUS_PORF)
+		dev_warn(&client->dev, "Voltage low, data loss detected.\n");
+
+	if (status & RV3028_STATUS_AF)
+		dev_warn(&client->dev, "An alarm may have been missed.\n");
+
+	rv3028->rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(rv3028->rtc)) {
+		return PTR_ERR(rv3028->rtc);
+	}
+
+	if (client->irq > 0) {
+		ret = devm_request_threaded_irq(&client->dev, client->irq,
+						NULL, rv3028_handle_irq,
+						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+						"rv3028", rv3028);
+		if (ret) {
+			dev_warn(&client->dev, "unable to request IRQ, alarms disabled\n");
+			client->irq = 0;
+		} else {
+			rv3028_rtc_ops.read_alarm = rv3028_get_alarm;
+			rv3028_rtc_ops.set_alarm = rv3028_set_alarm;
+			rv3028_rtc_ops.alarm_irq_enable = rv3028_alarm_irq_enable;
+		}
+	}
+
+	ret = regmap_update_bits(rv3028->regmap, RV3028_CTRL1,
+				 RV3028_CTRL1_WADA, RV3028_CTRL1_WADA);
+	if (ret)
+		return ret;
+
+	/* setup timestamping */
+	ret = regmap_update_bits(rv3028->regmap, RV3028_CTRL2,
+				 RV3028_CTRL2_EIE | RV3028_CTRL2_TSE,
+				 RV3028_CTRL2_EIE | RV3028_CTRL2_TSE);
+	if (ret)
+		return ret;
+
+	/* setup trickle charger */
+	if (!device_property_read_u32(&client->dev, "trickle-resistor-ohms",
+				      &ohms)) {
+		int i;
+
+		for (i = 0; i < ARRAY_SIZE(rv3028_trickle_resistors); i++)
+			if (ohms == rv3028_trickle_resistors[i])
+				break;
+
+		if (i < ARRAY_SIZE(rv3028_trickle_resistors)) {
+			ret = regmap_update_bits(rv3028->regmap, RV3028_BACKUP,
+						 RV3028_BACKUP_TCE |
+						 RV3028_BACKUP_TCR_MASK,
+						 RV3028_BACKUP_TCE | i);
+			if (ret)
+				return ret;
+		} else {
+			dev_warn(&client->dev, "invalid trickle resistor value\n");
+		}
+	}
+
+	ret = rtc_add_group(rv3028->rtc, &rv3028_attr_group);
+	if (ret)
+		return ret;
+
+	rv3028->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rv3028->rtc->range_max = RTC_TIMESTAMP_END_2099;
+	rv3028->rtc->ops = &rv3028_rtc_ops;
+	ret = rtc_register_device(rv3028->rtc);
+	if (ret)
+		return ret;
+
+	nvmem_cfg.priv = rv3028->regmap;
+	rtc_nvmem_register(rv3028->rtc, &nvmem_cfg);
+	eeprom_cfg.priv = rv3028->regmap;
+	rtc_nvmem_register(rv3028->rtc, &eeprom_cfg);
+
+	rv3028->rtc->max_user_freq = 1;
+
+	return 0;
+}
+
+static const struct of_device_id rv3028_of_match[] = {
+	{ .compatible = "microcrystal,rv3028", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, rv3028_of_match);
+
+static struct i2c_driver rv3028_driver = {
+	.driver = {
+		.name = "rtc-rv3028",
+		.of_match_table = of_match_ptr(rv3028_of_match),
+	},
+	.probe_new	= rv3028_probe,
+};
+module_i2c_driver(rv3028_driver);
+
+MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@bootlin.com>");
+MODULE_DESCRIPTION("Micro Crystal RV3028 RTC driver");
+MODULE_LICENSE("GPL v2");