rtc: add rtc-m41t80 driver

This is a new-style i2c driver for ST M41T80 series RTC chip, derived from
works by Alexander Bigga <ab@mycable.de> who wrote the original
rtc-m41txx.c based on drivers/i2c/chips/m41t00.c driver.

This driver supports M41T8[0-4] and M41ST8[457].  The old m41t00 driver
supports M41T00, M41T81 and M41T85(M41ST85).  While the M41T00 chip is now
supported by rtc-ds1307 driver, this driver does not include support for
the chip.

[akpm@linux-foundation.org: remove bogus `static']
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Alexander Bigga <ab@mycable.de>
Acked-by: Mark A. Greer <mgreer@mvista.com>
Cc: David Brownell <david-b@pacbell.net>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 642 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 25bea05ffaaa..fb9ce745cd30 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -212,6 +212,18 @@ config RTC_DRV_PCF8583
           This driver can also be built as a module. If so, the module
           will be called rtc-pcf8583.
 
+config RTC_DRV_M41T80
+        tristate "ST M41T80 series RTC"
+        depends on RTC_CLASS && I2C
+        help
+          If you say Y here you will get support for the
+          ST M41T80 RTC chips series. Currently following chips are
+          supported: M41T80, M41T81, M41T82, M41T83, M41ST84, M41ST85
+          and M41ST87.
+
+          This driver can also be built as a module. If so, the module
+          will be called rtc-m41t80.
+
 comment "SPI RTC drivers"
         depends on RTC_CLASS && SPI_MASTER
 
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 5fb1c102f30e..6da5102e0f21 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_RTC_DRV_PCF8583)	+= rtc-pcf8583.o
 obj-$(CONFIG_RTC_DRV_RS5C372)   += rtc-rs5c372.o
 obj-$(CONFIG_RTC_DRV_S3C)       += rtc-s3c.o
 obj-$(CONFIG_RTC_DRV_RS5C348)   += rtc-rs5c348.o
+obj-$(CONFIG_RTC_DRV_M41T80)    += rtc-m41t80.o
 obj-$(CONFIG_RTC_DRV_M48T86)    += rtc-m48t86.o
 obj-$(CONFIG_RTC_DRV_DS1553)    += rtc-ds1553.o
 obj-$(CONFIG_RTC_DRV_RS5C313)   += rtc-rs5c313.o
diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
new file mode 100644
index 000000000000..4875a4444216
--- /dev/null
+++ b/drivers/rtc/rtc-m41t80.c
@@ -0,0 +1,629 @@
+/*
+ * I2C client/driver for the ST M41T80 family of i2c rtc chips.
+ *
+ * Author: Alexander Bigga <ab@mycable.de>
+ *
+ * Based on m41t00.c by Mark A. Greer <mgreer@mvista.com>
+ *
+ * 2006 (c) mycable GmbH
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/i2c.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+
+#define M41T80_REG_SSEC 0
+#define M41T80_REG_SEC  1
+#define M41T80_REG_MIN  2
+#define M41T80_REG_HOUR 3
+#define M41T80_REG_WDAY 4
+#define M41T80_REG_DAY  5
+#define M41T80_REG_MON  6
+#define M41T80_REG_YEAR 7
+#define M41T80_REG_ALARM_MON    0xa
+#define M41T80_REG_ALARM_DAY    0xb
+#define M41T80_REG_ALARM_HOUR   0xc
+#define M41T80_REG_ALARM_MIN    0xd
+#define M41T80_REG_ALARM_SEC    0xe
+#define M41T80_REG_FLAGS        0xf
+#define M41T80_REG_SQW  0x13
+
+#define M41T80_DATETIME_REG_SIZE        (M41T80_REG_YEAR + 1)
+#define M41T80_ALARM_REG_SIZE   \
+        (M41T80_REG_ALARM_SEC + 1 - M41T80_REG_ALARM_MON)
+
+#define M41T80_SEC_ST           (1 << 7)        /* ST: Stop Bit */
+#define M41T80_ALMON_AFE        (1 << 7)        /* AFE: AF Enable Bit */
+#define M41T80_ALMON_SQWE       (1 << 6)        /* SQWE: SQW Enable Bit */
+#define M41T80_ALHOUR_HT        (1 << 6)        /* HT: Halt Update Bit */
+#define M41T80_FLAGS_AF         (1 << 6)        /* AF: Alarm Flag Bit */
+#define M41T80_FLAGS_BATT_LOW   (1 << 4)        /* BL: Battery Low Bit */
+
+#define M41T80_FEATURE_HT       (1 << 0)
+#define M41T80_FEATURE_BL       (1 << 1)
+
+#define DRV_VERSION "0.05"
+
+struct m41t80_chip_info {
+        const char *name;
+        u8 features;
+};
+
+static const struct m41t80_chip_info m41t80_chip_info_tbl[] = {
+        {
+                .name           = "m41t80",
+                .features       = 0,
+        },
+        {
+                .name           = "m41t81",
+                .features       = M41T80_FEATURE_HT,
+        },
+        {
+                .name           = "m41t81s",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+        {
+                .name           = "m41t82",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+        {
+                .name           = "m41t83",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+        {
+                .name           = "m41st84",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+        {
+                .name           = "m41st85",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+        {
+                .name           = "m41st87",
+                .features       = M41T80_FEATURE_HT | M41T80_FEATURE_BL,
+        },
+};
+
+struct m41t80_data {
+        const struct m41t80_chip_info *chip;
+        struct rtc_device *rtc;
+};
+
+static int m41t80_get_datetime(struct i2c_client *client,
+                               struct rtc_time *tm)
+{
+        u8 buf[M41T80_DATETIME_REG_SIZE], dt_addr[1] = { M41T80_REG_SEC };
+        struct i2c_msg msgs[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1,
+                        .buf    = dt_addr,
+                },
+                {
+                        .addr   = client->addr,
+                        .flags  = I2C_M_RD,
+                        .len    = M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
+                        .buf    = buf + M41T80_REG_SEC,
+                },
+        };
+
+        if (i2c_transfer(client->adapter, msgs, 2) < 0) {
+                dev_err(&client->dev, "read error\n");
+                return -EIO;
+        }
+
+        tm->tm_sec = BCD2BIN(buf[M41T80_REG_SEC] & 0x7f);
+        tm->tm_min = BCD2BIN(buf[M41T80_REG_MIN] & 0x7f);
+        tm->tm_hour = BCD2BIN(buf[M41T80_REG_HOUR] & 0x3f);
+        tm->tm_mday = BCD2BIN(buf[M41T80_REG_DAY] & 0x3f);
+        tm->tm_wday = buf[M41T80_REG_WDAY] & 0x07;
+        tm->tm_mon = BCD2BIN(buf[M41T80_REG_MON] & 0x1f) - 1;
+
+        /* assume 20YY not 19YY, and ignore the Century Bit */
+        tm->tm_year = BCD2BIN(buf[M41T80_REG_YEAR]) + 100;
+        return 0;
+}
+
+/* Sets the given date and time to the real time clock. */
+static int m41t80_set_datetime(struct i2c_client *client, struct rtc_time *tm)
+{
+        u8 wbuf[1 + M41T80_DATETIME_REG_SIZE];
+        u8 *buf = &wbuf[1];
+        u8 dt_addr[1] = { M41T80_REG_SEC };
+        struct i2c_msg msgs_in[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1,
+                        .buf    = dt_addr,
+                },
+                {
+                        .addr   = client->addr,
+                        .flags  = I2C_M_RD,
+                        .len    = M41T80_DATETIME_REG_SIZE - M41T80_REG_SEC,
+                        .buf    = buf + M41T80_REG_SEC,
+                },
+        };
+        struct i2c_msg msgs[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1 + M41T80_DATETIME_REG_SIZE,
+                        .buf    = wbuf,
+                 },
+        };
+
+        /* Read current reg values into buf[1..7] */
+        if (i2c_transfer(client->adapter, msgs_in, 2) < 0) {
+                dev_err(&client->dev, "read error\n");
+                return -EIO;
+        }
+
+        wbuf[0] = 0; /* offset into rtc's regs */
+        /* Merge time-data and register flags into buf[0..7] */
+        buf[M41T80_REG_SSEC] = 0;
+        buf[M41T80_REG_SEC] =
+                BIN2BCD(tm->tm_sec) | (buf[M41T80_REG_SEC] & ~0x7f);
+        buf[M41T80_REG_MIN] =
+                BIN2BCD(tm->tm_min) | (buf[M41T80_REG_MIN] & ~0x7f);
+        buf[M41T80_REG_HOUR] =
+                BIN2BCD(tm->tm_hour) | (buf[M41T80_REG_HOUR] & ~0x3f) ;
+        buf[M41T80_REG_WDAY] =
+                (tm->tm_wday & 0x07) | (buf[M41T80_REG_WDAY] & ~0x07);
+        buf[M41T80_REG_DAY] =
+                BIN2BCD(tm->tm_mday) | (buf[M41T80_REG_DAY] & ~0x3f);
+        buf[M41T80_REG_MON] =
+                BIN2BCD(tm->tm_mon + 1) | (buf[M41T80_REG_MON] & ~0x1f);
+        /* assume 20YY not 19YY */
+        buf[M41T80_REG_YEAR] = BIN2BCD(tm->tm_year % 100);
+
+        if (i2c_transfer(client->adapter, msgs, 1) != 1) {
+                dev_err(&client->dev, "write error\n");
+                return -EIO;
+        }
+        return 0;
+}
+
+#if defined(CONFIG_RTC_INTF_PROC) || defined(CONFIG_RTC_INTF_PROC_MODULE)
+static int m41t80_rtc_proc(struct device *dev, struct seq_file *seq)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        struct m41t80_data *clientdata = i2c_get_clientdata(client);
+        u8 reg;
+
+        if (clientdata->chip->features & M41T80_FEATURE_BL) {
+                reg = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS);
+                seq_printf(seq, "battery\t\t: %s\n",
+                           (reg & M41T80_FLAGS_BATT_LOW) ? "exhausted" : "ok");
+        }
+        return 0;
+}
+#else
+#define m41t80_rtc_proc NULL
+#endif
+
+static int m41t80_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+        return m41t80_get_datetime(to_i2c_client(dev), tm);
+}
+
+static int m41t80_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+        return m41t80_set_datetime(to_i2c_client(dev), tm);
+}
+
+#if defined(CONFIG_RTC_INTF_DEV) || defined(CONFIG_RTC_INTF_DEV_MODULE)
+static int
+m41t80_rtc_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        int rc;
+
+        switch (cmd) {
+        case RTC_AIE_OFF:
+        case RTC_AIE_ON:
+                break;
+        default:
+                return -ENOIOCTLCMD;
+        }
+
+        rc = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_MON);
+        if (rc < 0)
+                goto err;
+        switch (cmd) {
+        case RTC_AIE_OFF:
+                rc &= ~M41T80_ALMON_AFE;
+                break;
+        case RTC_AIE_ON:
+                rc |= M41T80_ALMON_AFE;
+                break;
+        }
+        if (i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON, rc) < 0)
+                goto err;
+        return 0;
+err:
+        return -EIO;
+}
+#else
+#define m41t80_rtc_ioctl NULL
+#endif
+
+static int m41t80_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *t)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        u8 wbuf[1 + M41T80_ALARM_REG_SIZE];
+        u8 *buf = &wbuf[1];
+        u8 *reg = buf - M41T80_REG_ALARM_MON;
+        u8 dt_addr[1] = { M41T80_REG_ALARM_MON };
+        struct i2c_msg msgs_in[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1,
+                        .buf    = dt_addr,
+                },
+                {
+                        .addr   = client->addr,
+                        .flags  = I2C_M_RD,
+                        .len    = M41T80_ALARM_REG_SIZE,
+                        .buf    = buf,
+                },
+        };
+        struct i2c_msg msgs[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1 + M41T80_ALARM_REG_SIZE,
+                        .buf    = wbuf,
+                 },
+        };
+
+        if (i2c_transfer(client->adapter, msgs_in, 2) < 0) {
+                dev_err(&client->dev, "read error\n");
+                return -EIO;
+        }
+        reg[M41T80_REG_ALARM_MON] &= ~(0x1f | M41T80_ALMON_AFE);
+        reg[M41T80_REG_ALARM_DAY] = 0;
+        reg[M41T80_REG_ALARM_HOUR] &= ~(0x3f | 0x80);
+        reg[M41T80_REG_ALARM_MIN] = 0;
+        reg[M41T80_REG_ALARM_SEC] = 0;
+
+        wbuf[0] = M41T80_REG_ALARM_MON; /* offset into rtc's regs */
+        reg[M41T80_REG_ALARM_SEC] |= t->time.tm_sec >= 0 ?
+                BIN2BCD(t->time.tm_sec) : 0x80;
+        reg[M41T80_REG_ALARM_MIN] |= t->time.tm_min >= 0 ?
+                BIN2BCD(t->time.tm_min) : 0x80;
+        reg[M41T80_REG_ALARM_HOUR] |= t->time.tm_hour >= 0 ?
+                BIN2BCD(t->time.tm_hour) : 0x80;
+        reg[M41T80_REG_ALARM_DAY] |= t->time.tm_mday >= 0 ?
+                BIN2BCD(t->time.tm_mday) : 0x80;
+        if (t->time.tm_mon >= 0)
+                reg[M41T80_REG_ALARM_MON] |= BIN2BCD(t->time.tm_mon + 1);
+        else
+                reg[M41T80_REG_ALARM_DAY] |= 0x40;
+
+        if (i2c_transfer(client->adapter, msgs, 1) != 1) {
+                dev_err(&client->dev, "write error\n");
+                return -EIO;
+        }
+
+        if (t->enabled) {
+                reg[M41T80_REG_ALARM_MON] |= M41T80_ALMON_AFE;
+                if (i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON,
+                                              reg[M41T80_REG_ALARM_MON]) < 0) {
+                        dev_err(&client->dev, "write error\n");
+                        return -EIO;
+                }
+        }
+        return 0;
+}
+
+static int m41t80_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *t)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        u8 buf[M41T80_ALARM_REG_SIZE + 1]; /* all alarm regs and flags */
+        u8 dt_addr[1] = { M41T80_REG_ALARM_MON };
+        u8 *reg = buf - M41T80_REG_ALARM_MON;
+        struct i2c_msg msgs[] = {
+                {
+                        .addr   = client->addr,
+                        .flags  = 0,
+                        .len    = 1,
+                        .buf    = dt_addr,
+                },
+                {
+                        .addr   = client->addr,
+                        .flags  = I2C_M_RD,
+                        .len    = M41T80_ALARM_REG_SIZE + 1,
+                        .buf    = buf,
+                },
+        };
+
+        if (i2c_transfer(client->adapter, msgs, 2) < 0) {
+                dev_err(&client->dev, "read error\n");
+                return -EIO;
+        }
+        t->time.tm_sec = -1;
+        t->time.tm_min = -1;
+        t->time.tm_hour = -1;
+        t->time.tm_mday = -1;
+        t->time.tm_mon = -1;
+        if (!(reg[M41T80_REG_ALARM_SEC] & 0x80))
+                t->time.tm_sec = BCD2BIN(reg[M41T80_REG_ALARM_SEC] & 0x7f);
+        if (!(reg[M41T80_REG_ALARM_MIN] & 0x80))
+                t->time.tm_min = BCD2BIN(reg[M41T80_REG_ALARM_MIN] & 0x7f);
+        if (!(reg[M41T80_REG_ALARM_HOUR] & 0x80))
+                t->time.tm_hour = BCD2BIN(reg[M41T80_REG_ALARM_HOUR] & 0x3f);
+        if (!(reg[M41T80_REG_ALARM_DAY] & 0x80))
+                t->time.tm_mday = BCD2BIN(reg[M41T80_REG_ALARM_DAY] & 0x3f);
+        if (!(reg[M41T80_REG_ALARM_DAY] & 0x40))
+                t->time.tm_mon = BCD2BIN(reg[M41T80_REG_ALARM_MON] & 0x1f) - 1;
+        t->time.tm_year = -1;
+        t->time.tm_wday = -1;
+        t->time.tm_yday = -1;
+        t->time.tm_isdst = -1;
+        t->enabled = !!(reg[M41T80_REG_ALARM_MON] & M41T80_ALMON_AFE);
+        t->pending = !!(reg[M41T80_REG_FLAGS] & M41T80_FLAGS_AF);
+        return 0;
+}
+
+static struct rtc_class_ops m41t80_rtc_ops = {
+        .read_time = m41t80_rtc_read_time,
+        .set_time = m41t80_rtc_set_time,
+        .read_alarm = m41t80_rtc_read_alarm,
+        .set_alarm = m41t80_rtc_set_alarm,
+        .proc = m41t80_rtc_proc,
+        .ioctl = m41t80_rtc_ioctl,
+};
+
+#if defined(CONFIG_RTC_INTF_SYSFS) || defined(CONFIG_RTC_INTF_SYSFS_MODULE)
+static ssize_t m41t80_sysfs_show_flags(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        int val;
+
+        val = i2c_smbus_read_byte_data(client, M41T80_REG_FLAGS);
+        if (val < 0)
+                return -EIO;
+        return sprintf(buf, "%#x\n", val);
+}
+static DEVICE_ATTR(flags, S_IRUGO, m41t80_sysfs_show_flags, NULL);
+
+static ssize_t m41t80_sysfs_show_sqwfreq(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        int val;
+
+        val = i2c_smbus_read_byte_data(client, M41T80_REG_SQW);
+        if (val < 0)
+                return -EIO;
+        val = (val >> 4) & 0xf;
+        switch (val) {
+        case 0:
+                break;
+        case 1:
+                val = 32768;
+                break;
+        default:
+                val = 32768 >> val;
+        }
+        return sprintf(buf, "%d\n", val);
+}
+static ssize_t m41t80_sysfs_set_sqwfreq(struct device *dev,
+                                struct device_attribute *attr,
+                                const char *buf, size_t count)
+{
+        struct i2c_client *client = to_i2c_client(dev);
+        int almon, sqw;
+        int val = simple_strtoul(buf, NULL, 0);
+
+        if (val) {
+                if (!is_power_of_2(val))
+                        return -EINVAL;
+                val = ilog2(val);
+                if (val == 15)
+                        val = 1;
+                else if (val < 14)
+                        val = 15 - val;
+                else
+                        return -EINVAL;
+        }
+        /* disable SQW, set SQW frequency & re-enable */
+        almon = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_MON);
+        if (almon < 0)
+                return -EIO;
+        sqw = i2c_smbus_read_byte_data(client, M41T80_REG_SQW);
+        if (sqw < 0)
+                return -EIO;
+        sqw = (sqw & 0x0f) | (val << 4);
+        if (i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON,
+                                      almon & ~M41T80_ALMON_SQWE) < 0 ||
+            i2c_smbus_write_byte_data(client, M41T80_REG_SQW, sqw) < 0)
+                return -EIO;
+        if (val && i2c_smbus_write_byte_data(client, M41T80_REG_ALARM_MON,
+                                             almon | M41T80_ALMON_SQWE) < 0)
+                return -EIO;
+        return count;
+}
+static DEVICE_ATTR(sqwfreq, S_IRUGO | S_IWUSR,
+                   m41t80_sysfs_show_sqwfreq, m41t80_sysfs_set_sqwfreq);
+
+static struct attribute *attrs[] = {
+        &dev_attr_flags.attr,
+        &dev_attr_sqwfreq.attr,
+        NULL,
+};
+static struct attribute_group attr_group = {
+        .attrs = attrs,
+};
+
+static int m41t80_sysfs_register(struct device *dev)
+{
+        return sysfs_create_group(&dev->kobj, &attr_group);
+}
+#else
+static int m41t80_sysfs_register(struct device *dev)
+{
+        return 0;
+}
+#endif
+
+/*
+ *****************************************************************************
+ *
+ *      Driver Interface
+ *
+ *****************************************************************************
+ */
+static int m41t80_probe(struct i2c_client *client)
+{
+        int i, rc = 0;
+        struct rtc_device *rtc = NULL;
+        struct rtc_time tm;
+        const struct m41t80_chip_info *chip;
+        struct m41t80_data *clientdata = NULL;
+
+        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C
+                                     | I2C_FUNC_SMBUS_BYTE_DATA)) {
+                rc = -ENODEV;
+                goto exit;
+        }
+
+        dev_info(&client->dev,
+                 "chip found, driver version " DRV_VERSION "\n");
+
+        chip = NULL;
+        for (i = 0; i < ARRAY_SIZE(m41t80_chip_info_tbl); i++) {
+                if (!strcmp(m41t80_chip_info_tbl[i].name, client->name)) {
+                        chip = &m41t80_chip_info_tbl[i];
+                        break;
+                }
+        }
+        if (!chip) {
+                dev_err(&client->dev, "%s is not supported\n", client->name);
+                rc = -ENODEV;
+                goto exit;
+        }
+
+        clientdata = kzalloc(sizeof(*clientdata), GFP_KERNEL);
+        if (!clientdata) {
+                rc = -ENOMEM;
+                goto exit;
+        }
+
+        rtc = rtc_device_register(client->name, &client->dev,
+                                  &m41t80_rtc_ops, THIS_MODULE);
+        if (IS_ERR(rtc)) {
+                rc = PTR_ERR(rtc);
+                rtc = NULL;
+                goto exit;
+        }
+
+        clientdata->rtc = rtc;
+        clientdata->chip = chip;
+        i2c_set_clientdata(client, clientdata);
+
+        /* Make sure HT (Halt Update) bit is cleared */
+        rc = i2c_smbus_read_byte_data(client, M41T80_REG_ALARM_HOUR);
+        if (rc < 0)
+                goto ht_err;
+
+        if (rc & M41T80_ALHOUR_HT) {
+                if (chip->features & M41T80_FEATURE_HT) {
+                        m41t80_get_datetime(client, &tm);
+                        dev_info(&client->dev, "HT bit was set!\n");
+                        dev_info(&client->dev,
+                                 "Power Down at "
+                                 "%04i-%02i-%02i %02i:%02i:%02i\n",
+                                 tm.tm_year + 1900,
+                                 tm.tm_mon + 1, tm.tm_mday, tm.tm_hour,
+                                 tm.tm_min, tm.tm_sec);
+                }
+                if (i2c_smbus_write_byte_data(client,
+                                              M41T80_REG_ALARM_HOUR,
+                                              rc & ~M41T80_ALHOUR_HT) < 0)
+                        goto ht_err;
+        }
+
+        /* Make sure ST (stop) bit is cleared */
+        rc = i2c_smbus_read_byte_data(client, M41T80_REG_SEC);
+        if (rc < 0)
+                goto st_err;
+
+        if (rc & M41T80_SEC_ST) {
+                if (i2c_smbus_write_byte_data(client, M41T80_REG_SEC,
+                                              rc & ~M41T80_SEC_ST) < 0)
+                        goto st_err;
+        }
+
+        rc = m41t80_sysfs_register(&client->dev);
+        if (rc)
+                goto exit;
+
+        return 0;
+
+st_err:
+        rc = -EIO;
+        dev_err(&client->dev, "Can't clear ST bit\n");
+        goto exit;
+ht_err:
+        rc = -EIO;
+        dev_err(&client->dev, "Can't clear HT bit\n");
+        goto exit;
+
+exit:
+        if (rtc)
+                rtc_device_unregister(rtc);
+        kfree(clientdata);
+        return rc;
+}
+
+static int m41t80_remove(struct i2c_client *client)
+{
+        struct m41t80_data *clientdata = i2c_get_clientdata(client);
+        struct rtc_device *rtc = clientdata->rtc;
+
+        if (rtc)
+                rtc_device_unregister(rtc);
+        kfree(clientdata);
+
+        return 0;
+}
+
+static struct i2c_driver m41t80_driver = {
+        .driver = {
+                .name = "m41t80",
+        },
+        .probe = m41t80_probe,
+        .remove = m41t80_remove,
+};
+
+static int __init m41t80_rtc_init(void)
+{
+        return i2c_add_driver(&m41t80_driver);
+}
+
+static void __exit m41t80_rtc_exit(void)
+{
+        i2c_del_driver(&m41t80_driver);
+}
+
+MODULE_AUTHOR("Alexander Bigga <ab@mycable.de>");
+MODULE_DESCRIPTION("ST Microelectronics M41T80 series RTC I2C Client Driver");
+MODULE_LICENSE("GPL");
+MODULE_VERSION(DRV_VERSION);
+
+module_init(m41t80_rtc_init);
+module_exit(m41t80_rtc_exit);