/*
 * rtc-ds1307.c - RTC driver for some mostly-compatible I2C chips.
 *
 *  Copyright (C) 2005 James Chapman (ds1337 core)
 *  Copyright (C) 2006 David Brownell
 *  Copyright (C) 2009 Matthias Fuchs (rx8025 support)
 *
 * 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/i2c.h>
#include <linux/string.h>
#include <linux/rtc.h>
#include <linux/bcd.h>



/* We can't determine type by probing, but if we expect pre-Linux code
 * to have set the chip up as a clock (turning on the oscillator and
 * setting the date and time), Linux can ignore the non-clock features.
 * That's a natural job for a factory or repair bench.
 */
enum ds_type {
        ds_1307,
        ds_1337,
        ds_1338,
        ds_1339,
        ds_1340,
        ds_1388,
        ds_3231,
        m41t00,
        mcp7941x,
        rx_8025,
        // rs5c372 too?  different address...
};


/* RTC registers don't differ much, except for the century flag */
#define DS1307_REG_SECS         0x00    /* 00-59 */
#       define DS1307_BIT_CH            0x80
#       define DS1340_BIT_nEOSC         0x80
#       define MCP7941X_BIT_ST          0x80
#define DS1307_REG_MIN          0x01    /* 00-59 */
#define DS1307_REG_HOUR         0x02    /* 00-23, or 1-12{am,pm} */
#       define DS1307_BIT_12HR          0x40    /* in REG_HOUR */
#       define DS1307_BIT_PM            0x20    /* in REG_HOUR */
#       define DS1340_BIT_CENTURY_EN    0x80    /* in REG_HOUR */
#       define DS1340_BIT_CENTURY       0x40    /* in REG_HOUR */
#define DS1307_REG_WDAY         0x03    /* 01-07 */
#       define MCP7941X_BIT_VBATEN      0x08
#define DS1307_REG_MDAY         0x04    /* 01-31 */
#define DS1307_REG_MONTH        0x05    /* 01-12 */
#       define DS1337_BIT_CENTURY       0x80    /* in REG_MONTH */
#define DS1307_REG_YEAR         0x06    /* 00-99 */

/* Other registers (control, status, alarms, trickle charge, NVRAM, etc)
 * start at 7, and they differ a LOT. Only control and status matter for
 * basic RTC date and time functionality; be careful using them.
 */
#define DS1307_REG_CONTROL      0x07            /* or ds1338 */
#       define DS1307_BIT_OUT           0x80
#       define DS1338_BIT_OSF           0x20
#       define DS1307_BIT_SQWE          0x10
#       define DS1307_BIT_RS1           0x02
#       define DS1307_BIT_RS0           0x01
#define DS1337_REG_CONTROL      0x0e
#       define DS1337_BIT_nEOSC         0x80
#       define DS1339_BIT_BBSQI         0x20
#       define DS3231_BIT_BBSQW         0x40 /* same as BBSQI */
#       define DS1337_BIT_RS2           0x10
#       define DS1337_BIT_RS1           0x08
#       define DS1337_BIT_INTCN         0x04
#       define DS1337_BIT_A2IE          0x02
#       define DS1337_BIT_A1IE          0x01
#define DS1340_REG_CONTROL      0x07
#       define DS1340_BIT_OUT           0x80
#       define DS1340_BIT_FT            0x40
#       define DS1340_BIT_CALIB_SIGN    0x20
#       define DS1340_M_CALIBRATION     0x1f
#define DS1340_REG_FLAG         0x09
#       define DS1340_BIT_OSF           0x80
#define DS1337_REG_STATUS       0x0f
#       define DS1337_BIT_OSF           0x80
#       define DS1337_BIT_A2I           0x02
#       define DS1337_BIT_A1I           0x01
#define DS1339_REG_ALARM1_SECS  0x07
#define DS1339_REG_TRICKLE      0x10

#define RX8025_REG_CTRL1        0x0e
#       define RX8025_BIT_2412          0x20
#define RX8025_REG_CTRL2        0x0f
#       define RX8025_BIT_PON           0x10
#       define RX8025_BIT_VDET          0x40
#       define RX8025_BIT_XST           0x20


struct ds1307 {
        u8                      offset; /* register's offset */
        u8                      regs[11];
        enum ds_type            type;
        unsigned long           flags;
#define HAS_NVRAM       0               /* bit 0 == sysfs file active */
#define HAS_ALARM       1               /* bit 1 == irq claimed */
        struct i2c_client       *client;
        struct rtc_device       *rtc;
        struct work_struct      work;
        s32 (*read_block_data)(const struct i2c_client *client, u8 command,
                               u8 length, u8 *values);
        s32 (*write_block_data)(const struct i2c_client *client, u8 command,
                                u8 length, const u8 *values);
};

struct chip_desc {
        unsigned                nvram56:1;
        unsigned                alarm:1;
};

static const struct chip_desc chips[] = {
[ds_1307] = {
        .nvram56        = 1,
},
[ds_1337] = {
        .alarm          = 1,
},
[ds_1338] = {
        .nvram56        = 1,
},
[ds_1339] = {
        .alarm          = 1,
},
[ds_1340] = {
},
[ds_3231] = {
        .alarm          = 1,
},
[m41t00] = {
},
[mcp7941x] = {
},
[rx_8025] = {
}, };

static const struct i2c_device_id ds1307_id[] = {
        { "ds1307", ds_1307 },
        { "ds1337", ds_1337 },
        { "ds1338", ds_1338 },
        { "ds1339", ds_1339 },
        { "ds1388", ds_1388 },
        { "ds1340", ds_1340 },
        { "ds3231", ds_3231 },
        { "m41t00", m41t00 },
        { "mcp7941x", mcp7941x },
        { "pt7c4338", ds_1307 },
        { "rx8025", rx_8025 },
        { }
};
MODULE_DEVICE_TABLE(i2c, ds1307_id);

/*----------------------------------------------------------------------*/

#define BLOCK_DATA_MAX_TRIES 10

static s32 ds1307_read_block_data_once(const struct i2c_client *client,
                                       u8 command, u8 length, u8 *values)
{
        s32 i, data;

        for (i = 0; i < length; i++) {
                data = i2c_smbus_read_byte_data(client, command + i);
                if (data < 0)
                        return data;
                values[i] = data;
        }
        return i;
}

static s32 ds1307_read_block_data(const struct i2c_client *client, u8 command,
                                  u8 length, u8 *values)
{
        u8 oldvalues[I2C_SMBUS_BLOCK_MAX];
        s32 ret;
        int tries = 0;

        dev_dbg(&client->dev, "ds1307_read_block_data (length=%d)\n", length);
        ret = ds1307_read_block_data_once(client, command, length, values);
        if (ret < 0)
                return ret;
        do {
                if (++tries > BLOCK_DATA_MAX_TRIES) {
                        dev_err(&client->dev,
                                "ds1307_read_block_data failed\n");
                        return -EIO;
                }
                memcpy(oldvalues, values, length);
                ret = ds1307_read_block_data_once(client, command, length,
                                                  values);
                if (ret < 0)
                        return ret;
        } while (memcmp(oldvalues, values, length));
        return length;
}

static s32 ds1307_write_block_data(const struct i2c_client *client, u8 command,
                                   u8 length, const u8 *values)
{
        u8 currvalues[I2C_SMBUS_BLOCK_MAX];
        int tries = 0;

        dev_dbg(&client->dev, "ds1307_write_block_data (length=%d)\n", length);
        do {
                s32 i, ret;

                if (++tries > BLOCK_DATA_MAX_TRIES) {
                        dev_err(&client->dev,
                                "ds1307_write_block_data failed\n");
                        return -EIO;
                }
                for (i = 0; i < length; i++) {
                        ret = i2c_smbus_write_byte_data(client, command + i,
                                                        values[i]);
                        if (ret < 0)
                                return ret;
                }
                ret = ds1307_read_block_data_once(client, command, length,
                                                  currvalues);
                if (ret < 0)
                        return ret;
        } while (memcmp(currvalues, values, length));
        return length;
}

/*----------------------------------------------------------------------*/

/*
 * The IRQ logic includes a "real" handler running in IRQ context just
 * long enough to schedule this workqueue entry.   We need a task context
 * to talk to the RTC, since I2C I/O calls require that; and disable the
 * IRQ until we clear its status on the chip, so that this handler can
 * work with any type of triggering (not just falling edge).
 *
 * The ds1337 and ds1339 both have two alarms, but we only use the first
 * one (with a "seconds" field).  For ds1337 we expect nINTA is our alarm
 * signal; ds1339 chips have only one alarm signal.
 */
static void ds1307_work(struct work_struct *work)
{
        struct ds1307           *ds1307;
        struct i2c_client       *client;
        struct mutex            *lock;
        int                     stat, control;

        ds1307 = container_of(work, struct ds1307, work);
        client = ds1307->client;
        lock = &ds1307->rtc->ops_lock;

        mutex_lock(lock);
        stat = i2c_smbus_read_byte_data(client, DS1337_REG_STATUS);
        if (stat < 0)
                goto out;

        if (stat & DS1337_BIT_A1I) {
                stat &= ~DS1337_BIT_A1I;
                i2c_smbus_write_byte_data(client, DS1337_REG_STATUS, stat);

                control = i2c_smbus_read_byte_data(client, DS1337_REG_CONTROL);
                if (control < 0)
                        goto out;

                control &= ~DS1337_BIT_A1IE;
                i2c_smbus_write_byte_data(client, DS1337_REG_CONTROL, control);

                rtc_update_irq(ds1307->rtc, 1, RTC_AF | RTC_IRQF);
        }

out:
        if (test_bit(HAS_ALARM, &ds1307->flags))
                enable_irq(client->irq);
        mutex_unlock(lock);
}

static irqreturn_t ds1307_irq(int irq, void *dev_id)
{
        struct i2c_client       *client = dev_id;
        struct ds1307           *ds1307 = i2c_get_clientdata(client);

        disable_irq_nosync(irq);
        schedule_work(&ds1307->work);
        return IRQ_HANDLED;
}

/*----------------------------------------------------------------------*/

static int ds1307_get_time(struct device *dev, struct rtc_time *t)
{
        struct ds1307   *ds1307 = dev_get_drvdata(dev);
        int             tmp;

        /* read the RTC date and time registers all at once */
        tmp = ds1307->read_block_data(ds1307->client,
                ds1307->offset, 7, ds1307->regs);
        if (tmp != 7) {
                dev_err(dev, "%s error %d\n", "read", tmp);
                return -EIO;
        }

        dev_dbg(dev, "%s: %02x %02x %02x %02x %02x %02x %02x\n",
                        "read",
                        ds1307->regs[0], ds1307->regs[1],
                        ds1307->regs[2], ds1307->regs[3],
                        ds1307->regs[4], ds1307->regs[5],
                        ds1307->regs[6]);

        t->tm_sec = bcd2bin(ds1307->regs[DS1307_REG_SECS] & 0x7f);
        t->tm_min = bcd2bin(ds1307->regs[DS1307_REG_MIN] & 0x7f);
        tmp = ds1307->regs[DS1307_REG_HOUR] & 0x3f;
        t->tm_hour = bcd2bin(tmp);
        t->tm_wday = bcd2bin(ds1307->regs[DS1307_REG_WDAY] & 0x07) - 1;
        t->tm_mday = bcd2bin(ds1307->regs[DS1307_REG_MDAY] & 0x3f);
        tmp = ds1307->regs[DS1307_REG_MONTH] & 0x1f;
        t->tm_mon = bcd2bin(tmp) - 1;

        /* assume 20YY not 19YY, and ignore DS1337_BIT_CENTURY */
        t->tm_year = bcd2bin(ds1307->regs[DS1307_REG_YEAR]) + 100;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "read", t->tm_sec, t->tm_min,
                t->tm_hour, t->tm_mday,
                t->tm_mon, t->tm_year, t->tm_wday);

        /* initial clock setting can be undefined */
        return rtc_valid_tm(t);
}

static int ds1307_set_time(struct device *dev, struct rtc_time *t)
{
        struct ds1307   *ds1307 = dev_get_drvdata(dev);
        int             result;
        int             tmp;
        u8              *buf = ds1307->regs;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
                "write", t->tm_sec, t->tm_min,
                t->tm_hour, t->tm_mday,
                t->tm_mon, t->tm_year, t->tm_wday);

        buf[DS1307_REG_SECS] = bin2bcd(t->tm_sec);
        buf[DS1307_REG_MIN] = bin2bcd(t->tm_min);
        buf[DS1307_REG_HOUR] = bin2bcd(t->tm_hour);
        buf[DS1307_REG_WDAY] = bin2bcd(t->tm_wday + 1);
        buf[DS1307_REG_MDAY] = bin2bcd(t->tm_mday);
        buf[DS1307_REG_MONTH] = bin2bcd(t->tm_mon + 1);

        /* assume 20YY not 19YY */
        tmp = t->tm_year - 100;
        buf[DS1307_REG_YEAR] = bin2bcd(tmp);

        switch (ds1307->type) {
        case ds_1337:
        case ds_1339:
        case ds_3231:
                buf[DS1307_REG_MONTH] |= DS1337_BIT_CENTURY;
                break;
        case ds_1340:
                buf[DS1307_REG_HOUR] |= DS1340_BIT_CENTURY_EN
                                | DS1340_BIT_CENTURY;
                break;
        case mcp7941x:
                buf[DS1307_REG_SECS] |= MCP7941X_BIT_ST;
                buf[DS1307_REG_WDAY] |= MCP7941X_BIT_VBATEN;
                break;
        default:
                break;
        }

        dev_dbg(dev, "%s: %02x %02x %02x %02x %02x %02x %02x\n",
                "write", buf[0], buf[1], buf[2], buf[3],
                buf[4], buf[5], buf[6]);

        result = ds1307->write_block_data(ds1307->client,
                ds1307->offset, 7, buf);
        if (result < 0) {
                dev_err(dev, "%s error %d\n", "write", result);
                return result;
        }
        return 0;
}

static int ds1337_read_alarm(struct device *dev, struct rtc_wkalrm *t)
{
        struct i2c_client       *client = to_i2c_client(dev);
        struct ds1307           *ds1307 = i2c_get_clientdata(client);
        int                     ret;

        if (!test_bit(HAS_ALARM, &ds1307->flags))
                return -EINVAL;

        /* read all ALARM1, ALARM2, and status registers at once */
        ret = ds1307->read_block_data(client,
                        DS1339_REG_ALARM1_SECS, 9, ds1307->regs);
        if (ret != 9) {
                dev_err(dev, "%s error %d\n", "alarm read", ret);
                return -EIO;
        }

        dev_dbg(dev, "%s: %02x %02x %02x %02x, %02x %02x %02x, %02x %02x\n",
                        "alarm read",
                        ds1307->regs[0], ds1307->regs[1],
                        ds1307->regs[2], ds1307->regs[3],
                        ds1307->regs[4], ds1307->regs[5],
                        ds1307->regs[6], ds1307->regs[7],
                        ds1307->regs[8]);

        /* report alarm time (ALARM1); assume 24 hour and day-of-month modes,
         * and that all four fields are checked matches
         */
        t->time.tm_sec = bcd2bin(ds1307->regs[0] & 0x7f);
        t->time.tm_min = bcd2bin(ds1307->regs[1] & 0x7f);
        t->time.tm_hour = bcd2bin(ds1307->regs[2] & 0x3f);
        t->time.tm_mday = bcd2bin(ds1307->regs[3] & 0x3f);
        t->time.tm_mon = -1;
        t->time.tm_year = -1;
        t->time.tm_wday = -1;
        t->time.tm_yday = -1;
        t->time.tm_isdst = -1;

        /* ... and status */
        t->enabled = !!(ds1307->regs[7] & DS1337_BIT_A1IE);
        t->pending = !!(ds1307->regs[8] & DS1337_BIT_A1I);

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, enabled=%d, pending=%d\n",
                "alarm read", t->time.tm_sec, t->time.tm_min,
                t->time.tm_hour, t->time.tm_mday,
                t->enabled, t->pending);

        return 0;
}

static int ds1337_set_alarm(struct device *dev, struct rtc_wkalrm *t)
{
        struct i2c_client       *client = to_i2c_client(dev);
        struct ds1307           *ds1307 = i2c_get_clientdata(client);
        unsigned char           *buf = ds1307->regs;
        u8                      control, status;
        int                     ret;

        if (!test_bit(HAS_ALARM, &ds1307->flags))
                return -EINVAL;

        dev_dbg(dev, "%s secs=%d, mins=%d, "
                "hours=%d, mday=%d, enabled=%d, pending=%d\n",
                "alarm set", t->time.tm_sec, t->time.tm_min,
                t->time.tm_hour, t->time.tm_mday,
                t->enabled, t->pending);

        /* read current status of both alarms and the chip */
        ret = ds1307->read_block_data(client,
                        DS1339_REG_ALARM1_SECS, 9, buf);
        if (ret != 9) {
                dev_err(dev, "%s error %d\n", "alarm write", ret);
                return -EIO;
        }
        control = ds1307->regs[7];
        status = ds1307->regs[8];

        dev_dbg(dev, "%s: %02x %02x %02x %02x, %02x %02x %02x, %02x %02x\n",
                        "alarm set (old status)",
                        ds1307->regs[0], ds1307->regs[1],
                        ds1307->regs[2], ds1307->regs[3],
                        ds1307->regs[4], ds1307->regs[5],
                        ds1307->regs[6], control, status);

        /* set ALARM1, using 24 hour and day-of-month modes */
        buf[0] = bin2bcd(t->time.tm_sec);
        buf[1] = bin2bcd(t->time.tm_min);
        buf[2] = bin2bcd(t->time.tm_hour);
        buf[3] = bin2bcd(t->time.tm_mday);

        /* set ALARM2 to non-garbage */
        buf[4] = 0;
        buf[5] = 0;
        buf[6] = 0;

        /* optionally enable ALARM1 */
        buf[7] = control & ~(DS1337_BIT_A1IE | DS1337_BIT_A2IE);
        if (t->enabled) {
                dev_dbg(dev, "alarm IRQ armed\n");
                buf[7] |= DS1337_BIT_A1IE;      /* only ALARM1 is used */
        }
        buf[8] = status & ~(DS1337_BIT_A1I | DS1337_BIT_A2I);

        ret = ds1307->write_block_data(client,
                        DS1339_REG_ALARM1_SECS, 9, buf);
        if (ret < 0) {
                dev_err(dev, "can't set alarm time\n");
                return ret;
        }

        return 0;
}

static int ds1307_alarm_irq_enable(struct device *dev, unsigned int enabled)
{
        struct i2c_client       *client = to_i2c_client(dev);
        struct ds1307           *ds1307 = i2c_get_clientdata(client);
        int                     ret;

        if (!test_bit(HAS_ALARM, &ds1307->flags))
                return -ENOTTY;

        ret = i2c_smbus_read_byte_data(client, DS1337_REG_CONTROL);
        if (ret < 0)
                return ret;

        if (enabled)
                ret |= DS1337_BIT_A1IE;
        else
                ret &= ~DS1337_BIT_A1IE;

        ret = i2c_smbus_write_byte_data(client, DS1337_REG_CONTROL, ret);
        if (ret < 0)
                return ret;

        return 0;
}

static const struct rtc_class_ops ds13xx_rtc_ops = {
        .read_time      = ds1307_get_time,
        .set_time       = ds1307_set_time,
        .read_alarm     = ds1337_read_alarm,
        .set_alarm      = ds1337_set_alarm,
        .alarm_irq_enable = ds1307_alarm_irq_enable,
};

/*----------------------------------------------------------------------*/

#define NVRAM_SIZE      56

static ssize_t
ds1307_nvram_read(struct file *filp, struct kobject *kobj,
                struct bin_attribute *attr,
                char *buf, loff_t off, size_t count)
{
        struct i2c_client       *client;
        struct ds1307           *ds1307;
        int                     result;

        client = kobj_to_i2c_client(kobj);
        ds1307 = i2c_get_clientdata(client);

        if (unlikely(off >= NVRAM_SIZE))
                return 0;
        if ((off + count) > NVRAM_SIZE)
                count = NVRAM_SIZE - off;
        if (unlikely(!count))
                return count;

        result = ds1307->read_block_data(client, 8 + off, count, buf);
        if (result < 0)
                dev_err(&client->dev, "%s error %d\n", "nvram read", result);
        return result;
}

static ssize_t
ds1307_nvram_write(struct file *filp, struct kobject *kobj,
                struct bin_attribute *attr,
                char *buf, loff_t off, size_t count)
{
        struct i2c_client       *client;
        struct ds1307           *ds1307;
        int                     result;

        client = kobj_to_i2c_client(kobj);
        ds1307 = i2c_get_clientdata(client);

        if (unlikely(off >= NVRAM_SIZE))
                return -EFBIG;
        if ((off + count) > NVRAM_SIZE)
                count = NVRAM_SIZE - off;
        if (unlikely(!count))
                return count;

        result = ds1307->write_block_data(client, 8 + off, count, buf);
        if (result < 0) {
                dev_err(&client->dev, "%s error %d\n", "nvram write", result);
                return result;
        }
        return count;
}

static struct bin_attribute nvram = {
        .attr = {
                .name   = "nvram",
                .mode   = S_IRUGO | S_IWUSR,
        },

        .read   = ds1307_nvram_read,
        .write  = ds1307_nvram_write,
        .size   = NVRAM_SIZE,
};

/*----------------------------------------------------------------------*/

static struct i2c_driver ds1307_driver;

static int __devinit ds1307_probe(struct i2c_client *client,
                                  const struct i2c_device_id *id)
{
        struct ds1307           *ds1307;
        int                     err = -ENODEV;
        int                     tmp;
        const struct chip_desc  *chip = &chips[id->driver_data];
        struct i2c_adapter      *adapter = to_i2c_adapter(client->dev.parent);
        int                     want_irq = false;
        unsigned char           *buf;
        static const int        bbsqi_bitpos[] = {
                [ds_1337] = 0,
                [ds_1339] = DS1339_BIT_BBSQI,
                [ds_3231] = DS3231_BIT_BBSQW,
        };

        if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA)
            && !i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK))
                return -EIO;

        if (!(ds1307 = kzalloc(sizeof(struct ds1307), GFP_KERNEL)))
                return -ENOMEM;

        i2c_set_clientdata(client, ds1307);

        ds1307->client  = client;
        ds1307->type    = id->driver_data;
        ds1307->offset  = 0;

        buf = ds1307->regs;
        if (i2c_check_functionality(adapter, I2C_FUNC_SMBUS_I2C_BLOCK)) {
                ds1307->read_block_data = i2c_smbus_read_i2c_block_data;
                ds1307->write_block_data = i2c_smbus_write_i2c_block_data;
        } else {
                ds1307->read_block_data = ds1307_read_block_data;
                ds1307->write_block_data = ds1307_write_block_data;
        }

        switch (ds1307->type) {
        case ds_1337:
        case ds_1339:
        case ds_3231:
                /* has IRQ? */
                if (ds1307->client->irq > 0 && chip->alarm) {
                        INIT_WORK(&ds1307->work, ds1307_work);
                        want_irq = true;
                }
                /* get registers that the "rtc" read below won't read... */
                tmp = ds1307->read_block_data(ds1307->client,
                                DS1337_REG_CONTROL, 2, buf);
                if (tmp != 2) {
                        pr_debug("read error %d\n", tmp);
                        err = -EIO;
                        goto exit_free;
                }

                /* oscillator off?  turn it on, so clock can tick. */
                if (ds1307->regs[0] & DS1337_BIT_nEOSC)
                        ds1307->regs[0] &= ~DS1337_BIT_nEOSC;

                /* Using IRQ?  Disable the square wave and both alarms.
                 * For some variants, be sure alarms can trigger when we're
                 * running on Vbackup (BBSQI/BBSQW)
                 */
                if (want_irq) {
                        ds1307->regs[0] |= DS1337_BIT_INTCN
                                        | bbsqi_bitpos[ds1307->type];
                        ds1307->regs[0] &= ~(DS1337_BIT_A2IE | DS1337_BIT_A1IE);
                }

                i2c_smbus_write_byte_data(client, DS1337_REG_CONTROL,
                                                        ds1307->regs[0]);

                /* oscillator fault?  clear flag, and warn */
                if (ds1307->regs[1] & DS1337_BIT_OSF) {
                        i2c_smbus_write_byte_data(client, DS1337_REG_STATUS,
                                ds1307->regs[1] & ~DS1337_BIT_OSF);
                        dev_warn(&client->dev, "SET TIME!\n");
                }
                break;

        case rx_8025:
                tmp = i2c_smbus_read_i2c_block_data(ds1307->client,
                                RX8025_REG_CTRL1 << 4 | 0x08, 2, buf);
                if (tmp != 2) {
                        pr_debug("read error %d\n", tmp);
                        err = -EIO;
                        goto exit_free;
                }

                /* oscillator off?  turn it on, so clock can tick. */
                if (!(ds1307->regs[1] & RX8025_BIT_XST)) {
                        ds1307->regs[1] |= RX8025_BIT_XST;
                        i2c_smbus_write_byte_data(client,
                                                  RX8025_REG_CTRL2 << 4 | 0x08,
                                                  ds1307->regs[1]);
                        dev_warn(&client->dev,
                                 "oscillator stop detected - SET TIME!\n");
                }

                if (ds1307->regs[1] & RX8025_BIT_PON) {
                        ds1307->regs[1] &= ~RX8025_BIT_PON;
                        i2c_smbus_write_byte_data(client,
                                                  RX8025_REG_CTRL2 << 4 | 0x08,
                                                  ds1307->regs[1]);
                        dev_warn(&client->dev, "power-on detected\n");
                }

                if (ds1307->regs[1] & RX8025_BIT_VDET) {
                        ds1307->regs[1] &= ~RX8025_BIT_VDET;
                        i2c_smbus_write_byte_data(client,
                                                  RX8025_REG_CTRL2 << 4 | 0x08,
                                                  ds1307->regs[1]);
                        dev_warn(&client->dev, "voltage drop detected\n");
                }

                /* make sure we are running in 24hour mode */
                if (!(ds1307->regs[0] & RX8025_BIT_2412)) {
                        u8 hour;

                        /* switch to 24 hour mode */
                        i2c_smbus_write_byte_data(client,
                                                  RX8025_REG_CTRL1 << 4 | 0x08,
                                                  ds1307->regs[0] |
                                                  RX8025_BIT_2412);

                        tmp = i2c_smbus_read_i2c_block_data(ds1307->client,
                                        RX8025_REG_CTRL1 << 4 | 0x08, 2, buf);
                        if (tmp != 2) {
                                pr_debug("read error %d\n", tmp);
                                err = -EIO;
                                goto exit_free;
                        }

                        /* correct hour */
                        hour = bcd2bin(ds1307->regs[DS1307_REG_HOUR]);
                        if (hour == 12)
                                hour = 0;
                        if (ds1307->regs[DS1307_REG_HOUR] & DS1307_BIT_PM)
                                hour += 12;

                        i2c_smbus_write_byte_data(client,
                                                  DS1307_REG_HOUR << 4 | 0x08,
                                                  hour);
                }
                break;
        case ds_1388:
                ds1307->offset = 1; /* Seconds starts at 1 */
                break;
        default:
                break;
        }

read_rtc:
        /* read RTC registers */
        tmp = ds1307->read_block_data(ds1307->client, ds1307->offset, 8, buf);
        if (tmp != 8) {
                pr_debug("read error %d\n", tmp);
                err = -EIO;
                goto exit_free;
        }

        /* minimal sanity checking; some chips (like DS1340) don't
         * specify the extra bits as must-be-zero, but there are
         * still a few values that are clearly out-of-range.
         */
        tmp = ds1307->regs[DS1307_REG_SECS];
        switch (ds1307->type) {
        case ds_1307:
        case m41t00:
                /* clock halted?  turn it on, so clock can tick. */
                if (tmp & DS1307_BIT_CH) {
                        i2c_smbus_write_byte_data(client, DS1307_REG_SECS, 0);
                        dev_warn(&client->dev, "SET TIME!\n");
                        goto read_rtc;
                }
                break;
        case ds_1338:
                /* clock halted?  turn it on, so clock can tick. */
                if (tmp & DS1307_BIT_CH)
                        i2c_smbus_write_byte_data(client, DS1307_REG_SECS, 0);

                /* oscillator fault?  clear flag, and warn */
                if (ds1307->regs[DS1307_REG_CONTROL] & DS1338_BIT_OSF) {
                        i2c_smbus_write_byte_data(client, DS1307_REG_CONTROL,
                                        ds1307->regs[DS1307_REG_CONTROL]
                                        & ~DS1338_BIT_OSF);
                        dev_warn(&client->dev, "SET TIME!\n");
                        goto read_rtc;
                }
                break;
        case ds_1340:
                /* clock halted?  turn it on, so clock can tick. */
                if (tmp & DS1340_BIT_nEOSC)
                        i2c_smbus_write_byte_data(client, DS1307_REG_SECS, 0);

                tmp = i2c_smbus_read_byte_data(client, DS1340_REG_FLAG);
                if (tmp < 0) {
                        pr_debug("read error %d\n", tmp);
                        err = -EIO;
                        goto exit_free;
                }

                /* oscillator fault?  clear flag, and warn */
                if (tmp & DS1340_BIT_OSF) {
                        i2c_smbus_write_byte_data(client, DS1340_REG_FLAG, 0);
                        dev_warn(&client->dev, "SET TIME!\n");
                }
                break;
        case mcp7941x:
                /* make sure that the backup battery is enabled */
                if (!(ds1307->regs[DS1307_REG_WDAY] & MCP7941X_BIT_VBATEN)) {
                        i2c_smbus_write_byte_data(client, DS1307_REG_WDAY,
                                        ds1307->regs[DS1307_REG_WDAY]
                                        | MCP7941X_BIT_VBATEN);
                }

                /* clock halted?  turn it on, so clock can tick. */
                if (!(tmp & MCP7941X_BIT_ST)) {
                        i2c_smbus_write_byte_data(client, DS1307_REG_SECS,
                                        MCP7941X_BIT_ST);
                        dev_warn(&client->dev, "SET TIME!\n");
                        goto read_rtc;
                }

                break;
        case rx_8025:
        case ds_1337:
        case ds_1339:
        case ds_1388:
        case ds_3231:
                break;
        }

        tmp = ds1307->regs[DS1307_REG_HOUR];
        switch (ds1307->type) {
        case ds_1340:
        case m41t00:
                /* NOTE: ignores century bits; fix before deploying
                 * systems that will run through year 2100.
                 */
                break;
        case rx_8025:
                break;
        default:
                if (!(tmp & DS1307_BIT_12HR))
                        break;

                /* Be sure we're in 24 hour mode.  Multi-master systems
                 * take note...
                 */
                tmp = bcd2bin(tmp & 0x1f);
                if (tmp == 12)
                        tmp = 0;
                if (ds1307->regs[DS1307_REG_HOUR] & DS1307_BIT_PM)
                        tmp += 12;
                i2c_smbus_write_byte_data(client,
                                ds1307->offset + DS1307_REG_HOUR,
                                bin2bcd(tmp));
        }

        ds1307->rtc = rtc_device_register(client->name, &client->dev,
                                &ds13xx_rtc_ops, THIS_MODULE);
        if (IS_ERR(ds1307->rtc)) {
                err = PTR_ERR(ds1307->rtc);
                dev_err(&client->dev,
                        "unable to register the class device\n");
                goto exit_free;
        }

        if (want_irq) {
                err = request_irq(client->irq, ds1307_irq, IRQF_SHARED,
                          ds1307->rtc->name, client);
                if (err) {
                        dev_err(&client->dev,
                                "unable to request IRQ!\n");
                        goto exit_irq;
                }

                device_set_wakeup_capable(&client->dev, 1);
                set_bit(HAS_ALARM, &ds1307->flags);
                dev_dbg(&client->dev, "got IRQ %d\n", client->irq);
        }

        if (chip->nvram56) {
                err = sysfs_create_bin_file(&client->dev.kobj, &nvram);
                if (err == 0) {
                        set_bit(HAS_NVRAM, &ds1307->flags);
                        dev_info(&client->dev, "56 bytes nvram\n");
                }
        }

        return 0;

exit_irq:
        rtc_device_unregister(ds1307->rtc);
exit_free:
        kfree(ds1307);
        return err;
}

static int __devexit ds1307_remove(struct i2c_client *client)
{
        struct ds1307           *ds1307 = i2c_get_clientdata(client);

        if (test_and_clear_bit(HAS_ALARM, &ds1307->flags)) {
                free_irq(client->irq, client);
                cancel_work_sync(&ds1307->work);
        }

        if (test_and_clear_bit(HAS_NVRAM, &ds1307->flags))
                sysfs_remove_bin_file(&client->dev.kobj, &nvram);

        rtc_device_unregister(ds1307->rtc);
        kfree(ds1307);
        return 0;
}

static struct i2c_driver ds1307_driver = {
        .driver = {
                .name   = "rtc-ds1307",
                .owner  = THIS_MODULE,
        },
        .probe          = ds1307_probe,
        .remove         = __devexit_p(ds1307_remove),
        .id_table       = ds1307_id,
};

static int __init ds1307_init(void)
{
        return i2c_add_driver(&ds1307_driver);
}
module_init(ds1307_init);

static void __exit ds1307_exit(void)
{
        i2c_del_driver(&ds1307_driver);
}
module_exit(ds1307_exit);

MODULE_DESCRIPTION("RTC driver for DS1307 and similar chips");
MODULE_LICENSE("GPL");