path: root/drivers/rtc/rtc-ds1307.c

/*
 * 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>
#include <linux/rtc/ds1307.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,
	last_ds_type /* always last */
	/* 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 DS13XX_TRICKLE_CHARGER_MAGIC	0xa0

#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];
	u16			nvram_offset;
	struct bin_attribute	*nvram;
	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		alarm:1;
	u16			nvram_offset;
	u16			nvram_size;
	u16			trickle_charger_reg;
};

static const struct chip_desc chips[last_ds_type] = {
	[ds_1307] = {
		.nvram_offset	= 8,
		.nvram_size	= 56,
	},
	[ds_1337] = {
		.alarm		= 1,
	},
	[ds_1338] = {
		.nvram_offset	= 8,
		.nvram_size	= 56,
	},
	[ds_1339] = {
		.alarm		= 1,
		.trickle_charger_reg = 0x10,
	},
	[ds_1340] = {
		.trickle_charger_reg = 0x08,
	},
	[ds_1388] = {
		.trickle_charger_reg = 0x0a,
	},
	[ds_3231] = {
		.alarm		= 1,
	},
	[mcp7941x] = {
		/* this is battery backed SRAM */
		.nvram_offset	= 0x20,
		.nvram_size	= 0x40,
	},
};

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:
		/*
		 * these bits were cleared when preparing the date/time
		 * values and need to be set again before writing the
		 * buffer out to the device.
		 */
		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,
};

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

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 >= ds1307->nvram->size))
		return 0;
	if ((off + count) > ds1307->nvram->size)
		count = ds1307->nvram->size - off;
	if (unlikely(!count))
		return count;

	result = ds1307->read_block_data(client, ds1307->nvram_offset + 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 >= ds1307->nvram->size))
		return -EFBIG;
	if ((off + count) > ds1307->nvram->size)
		count = ds1307->nvram->size - off;
	if (unlikely(!count))
		return count;

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

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

static int 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;
	struct ds1307_platform_data *pdata = client->dev.platform_data;
	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;

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

	i2c_set_clientdata(client, ds1307);

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

	if (pdata && pdata->trickle_charger_setup && chip->trickle_charger_reg)
		i2c_smbus_write_byte_data(client, chip->trickle_charger_reg,
			DS13XX_TRICKLE_CHARGER_MAGIC | pdata->trickle_charger_setup);

	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:
		/* 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 (ds1307->client->irq > 0 && chip->alarm) {
			INIT_WORK(&ds1307->work, ds1307_work);

			ds1307->regs[0] |= DS1337_BIT_INTCN
					| bbsqi_bitpos[ds1307->type];
			ds1307->regs[0] &= ~(DS1337_BIT_A2IE | DS1337_BIT_A1IE);

			want_irq = true;
		}

		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;
	default:
		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->nvram_size) {
		ds1307->nvram = kzalloc(sizeof(struct bin_attribute),
							GFP_KERNEL);
		if (!ds1307->nvram) {
			err = -ENOMEM;
			goto exit_nvram;
		}
		ds1307->nvram->attr.name = "nvram";
		ds1307->nvram->attr.mode = S_IRUGO | S_IWUSR;
		sysfs_bin_attr_init(ds1307->nvram);
		ds1307->nvram->read = ds1307_nvram_read,
		ds1307->nvram->write = ds1307_nvram_write,
		ds1307->nvram->size = chip->nvram_size;
		ds1307->nvram_offset = chip->nvram_offset;
		err = sysfs_create_bin_file(&client->dev.kobj, ds1307->nvram);
		if (err) {
			kfree(ds1307->nvram);
			goto exit_nvram;
		}
		set_bit(HAS_NVRAM, &ds1307->flags);
		dev_info(&client->dev, "%zu bytes nvram\n", ds1307->nvram->size);
	}

	return 0;

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

static int 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, ds1307->nvram);
		kfree(ds1307->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		= ds1307_remove,
	.id_table	= ds1307_id,
};

module_i2c_driver(ds1307_driver);

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