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>

3 files changed, 742 insertions, 0 deletions

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");