drivers/rtc/rtc-isl12057.c - kernel/msm-4.9 - Gitiles

 /*
  * rtc-isl12057 - Driver for Intersil ISL12057 I2C Real Time Clock
  *
  * Copyright (C) 2013, Arnaud EBALARD <arno@natisbad.org>
  *
  * This work is largely based on Intersil ISL1208 driver developed by
  * Hebert Valerio Riedel <hvr@gnu.org>.
  *
  * Detailed datasheet on which this development is based is available here:
  *
  *  http://natisbad.org/NAS2/refs/ISL12057.pdf
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  */

 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/rtc.h>
 #include <linux/i2c.h>
 #include <linux/bcd.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/regmap.h>

 #define DRV_NAME "rtc-isl12057"

 /* RTC section */
 #define ISL12057_REG_RTC_SC	0x00	/* Seconds */
 #define ISL12057_REG_RTC_MN	0x01	/* Minutes */
 #define ISL12057_REG_RTC_HR	0x02	/* Hours */
 #define ISL12057_REG_RTC_HR_PM	BIT(5)	/* AM/PM bit in 12h format */
 #define ISL12057_REG_RTC_HR_MIL BIT(6)	/* 24h/12h format */
 #define ISL12057_REG_RTC_DW	0x03	/* Day of the Week */
 #define ISL12057_REG_RTC_DT	0x04	/* Date */
 #define ISL12057_REG_RTC_MO	0x05	/* Month */
 #define ISL12057_REG_RTC_MO_CEN	BIT(7)	/* Century bit */
 #define ISL12057_REG_RTC_YR	0x06	/* Year */
 #define ISL12057_RTC_SEC_LEN	7

 /* Alarm 1 section */
 #define ISL12057_REG_A1_SC	0x07	/* Alarm 1 Seconds */
 #define ISL12057_REG_A1_MN	0x08	/* Alarm 1 Minutes */
 #define ISL12057_REG_A1_HR	0x09	/* Alarm 1 Hours */
 #define ISL12057_REG_A1_HR_PM	BIT(5)	/* AM/PM bit in 12h format */
 #define ISL12057_REG_A1_HR_MIL	BIT(6)	/* 24h/12h format */
 #define ISL12057_REG_A1_DWDT	0x0A	/* Alarm 1 Date / Day of the week */
 #define ISL12057_REG_A1_DWDT_B	BIT(6)	/* DW / DT selection bit */
 #define ISL12057_A1_SEC_LEN	4

 /* Alarm 2 section */
 #define ISL12057_REG_A2_MN	0x0B	/* Alarm 2 Minutes */
 #define ISL12057_REG_A2_HR	0x0C	/* Alarm 2 Hours */
 #define ISL12057_REG_A2_DWDT	0x0D	/* Alarm 2 Date / Day of the week */
 #define ISL12057_A2_SEC_LEN	3

 /* Control/Status registers */
 #define ISL12057_REG_INT	0x0E
 #define ISL12057_REG_INT_A1IE	BIT(0)	/* Alarm 1 interrupt enable bit */
 #define ISL12057_REG_INT_A2IE	BIT(1)	/* Alarm 2 interrupt enable bit */
 #define ISL12057_REG_INT_INTCN	BIT(2)	/* Interrupt control enable bit */
 #define ISL12057_REG_INT_RS1	BIT(3)	/* Freq out control bit 1 */
 #define ISL12057_REG_INT_RS2	BIT(4)	/* Freq out control bit 2 */
 #define ISL12057_REG_INT_EOSC	BIT(7)	/* Oscillator enable bit */

 #define ISL12057_REG_SR		0x0F
 #define ISL12057_REG_SR_A1F	BIT(0)	/* Alarm 1 interrupt bit */
 #define ISL12057_REG_SR_A2F	BIT(1)	/* Alarm 2 interrupt bit */
 #define ISL12057_REG_SR_OSF	BIT(7)	/* Oscillator failure bit */

 /* Register memory map length */
 #define ISL12057_MEM_MAP_LEN	0x10

 struct isl12057_rtc_data {
 	struct regmap *regmap;
 	struct mutex lock;
 };

 static void isl12057_rtc_regs_to_tm(struct rtc_time *tm, u8 *regs)
 {
 	tm->tm_sec = bcd2bin(regs[ISL12057_REG_RTC_SC]);
 	tm->tm_min = bcd2bin(regs[ISL12057_REG_RTC_MN]);

 	if (regs[ISL12057_REG_RTC_HR] & ISL12057_REG_RTC_HR_MIL) { /* AM/PM */
 		tm->tm_hour = bcd2bin(regs[ISL12057_REG_RTC_HR] & 0x1f);
 		if (regs[ISL12057_REG_RTC_HR] & ISL12057_REG_RTC_HR_PM)
 			tm->tm_hour += 12;
 	} else {					    /* 24 hour mode */
 		tm->tm_hour = bcd2bin(regs[ISL12057_REG_RTC_HR] & 0x3f);
 	}

 	tm->tm_mday = bcd2bin(regs[ISL12057_REG_RTC_DT]);
 	tm->tm_wday = bcd2bin(regs[ISL12057_REG_RTC_DW]) - 1; /* starts at 1 */
 	tm->tm_mon  = bcd2bin(regs[ISL12057_REG_RTC_MO] & 0x1f) - 1; /* ditto */
 	tm->tm_year = bcd2bin(regs[ISL12057_REG_RTC_YR]) + 100;

 	/* Check if years register has overflown from 99 to 00 */
 	if (regs[ISL12057_REG_RTC_MO] & ISL12057_REG_RTC_MO_CEN)
 		tm->tm_year += 100;
 }

 static int isl12057_rtc_tm_to_regs(u8 *regs, struct rtc_time *tm)
 {
 	u8 century_bit;

 	/*
 	 * The clock has an 8 bit wide bcd-coded register for the year.
 	 * It also has a century bit encoded in MO flag which provides
 	 * information about overflow of year register from 99 to 00.
 	 * tm_year is an offset from 1900 and we are interested in the
 	 * 2000-2199 range, so any value less than 100 or larger than
 	 * 299 is invalid.
 	 */
 	if (tm->tm_year < 100 || tm->tm_year > 299)
 		return -EINVAL;

 	century_bit = (tm->tm_year > 199) ? ISL12057_REG_RTC_MO_CEN : 0;

 	regs[ISL12057_REG_RTC_SC] = bin2bcd(tm->tm_sec);
 	regs[ISL12057_REG_RTC_MN] = bin2bcd(tm->tm_min);
 	regs[ISL12057_REG_RTC_HR] = bin2bcd(tm->tm_hour); /* 24-hour format */
 	regs[ISL12057_REG_RTC_DT] = bin2bcd(tm->tm_mday);
 	regs[ISL12057_REG_RTC_MO] = bin2bcd(tm->tm_mon + 1) | century_bit;
 	regs[ISL12057_REG_RTC_YR] = bin2bcd(tm->tm_year % 100);
 	regs[ISL12057_REG_RTC_DW] = bin2bcd(tm->tm_wday + 1);

 	return 0;
 }

 /*
  * Try and match register bits w/ fixed null values to see whether we
  * are dealing with an ISL12057. Note: this function is called early
  * during init and hence does need mutex protection.
  */
 static int isl12057_i2c_validate_chip(struct regmap *regmap)
 {
 	u8 regs[ISL12057_MEM_MAP_LEN];
 	static const u8 mask[ISL12057_MEM_MAP_LEN] = { 0x80, 0x80, 0x80, 0xf8,
 						       0xc0, 0x60, 0x00, 0x00,
 						       0x00, 0x00, 0x00, 0x00,
 						       0x00, 0x00, 0x60, 0x7c };
 	int ret, i;

 	ret = regmap_bulk_read(regmap, 0, regs, ISL12057_MEM_MAP_LEN);
 	if (ret)
 		return ret;

 	for (i = 0; i < ISL12057_MEM_MAP_LEN; ++i) {
 		if (regs[i] & mask[i])	/* check if bits are cleared */
 			return -ENODEV;
 	}

 	return 0;
 }

 static int isl12057_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct isl12057_rtc_data *data = dev_get_drvdata(dev);
 	u8 regs[ISL12057_RTC_SEC_LEN];
 	unsigned int sr;
 	int ret;

 	mutex_lock(&data->lock);
 	ret = regmap_read(data->regmap, ISL12057_REG_SR, &sr);
 	if (ret) {
 		dev_err(dev, "%s: unable to read oscillator status flag (%d)\n",
 			__func__, ret);
 		goto out;
 	} else {
 		if (sr & ISL12057_REG_SR_OSF) {
 			ret = -ENODATA;
 			goto out;
 		}
 	}

 	ret = regmap_bulk_read(data->regmap, ISL12057_REG_RTC_SC, regs,
 			       ISL12057_RTC_SEC_LEN);
 	if (ret)
 		dev_err(dev, "%s: unable to read RTC time section (%d)\n",
 			__func__, ret);

 out:
 	mutex_unlock(&data->lock);

 	if (ret)
 		return ret;

 	isl12057_rtc_regs_to_tm(tm, regs);

 	return rtc_valid_tm(tm);
 }

 static int isl12057_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct isl12057_rtc_data *data = dev_get_drvdata(dev);
 	u8 regs[ISL12057_RTC_SEC_LEN];
 	int ret;

 	ret = isl12057_rtc_tm_to_regs(regs, tm);
 	if (ret)
 		return ret;

 	mutex_lock(&data->lock);
 	ret = regmap_bulk_write(data->regmap, ISL12057_REG_RTC_SC, regs,
 				ISL12057_RTC_SEC_LEN);
 	if (ret) {
 		dev_err(dev, "%s: unable to write RTC time section (%d)\n",
 			__func__, ret);
 		goto out;
 	}

 	/*
 	 * Now that RTC time has been updated, let's clear oscillator
 	 * failure flag, if needed.
 	 */
 	ret = regmap_update_bits(data->regmap, ISL12057_REG_SR,
 				 ISL12057_REG_SR_OSF, 0);
 	if (ret < 0)
 		dev_err(dev, "%s: unable to clear osc. failure bit (%d)\n",
 			__func__, ret);

 out:
 	mutex_unlock(&data->lock);

 	return ret;
 }

 /*
  * Check current RTC status and enable/disable what needs to be. Return 0 if
  * everything went ok and a negative value upon error. Note: this function
  * is called early during init and hence does need mutex protection.
  */
 static int isl12057_check_rtc_status(struct device *dev, struct regmap *regmap)
 {
 	int ret;

 	/* Enable oscillator if not already running */
 	ret = regmap_update_bits(regmap, ISL12057_REG_INT,
 				 ISL12057_REG_INT_EOSC, 0);
 	if (ret < 0) {
 		dev_err(dev, "%s: unable to enable oscillator (%d)\n",
 			__func__, ret);
 		return ret;
 	}

 	/* Clear alarm bit if needed */
 	ret = regmap_update_bits(regmap, ISL12057_REG_SR,
 				 ISL12057_REG_SR_A1F, 0);
 	if (ret < 0) {
 		dev_err(dev, "%s: unable to clear alarm bit (%d)\n",
 			__func__, ret);
 		return ret;
 	}

 	return 0;
 }

 static const struct rtc_class_ops rtc_ops = {
 	.read_time = isl12057_rtc_read_time,
 	.set_time = isl12057_rtc_set_time,
 };

 static struct regmap_config isl12057_rtc_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 };

 static int isl12057_probe(struct i2c_client *client,
 			  const struct i2c_device_id *id)
 {
 	struct device *dev = &client->dev;
 	struct isl12057_rtc_data *data;
 	struct rtc_device *rtc;
 	struct regmap *regmap;
 	int ret;

 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
 				     I2C_FUNC_SMBUS_BYTE_DATA |
 				     I2C_FUNC_SMBUS_I2C_BLOCK))
 		return -ENODEV;

 	regmap = devm_regmap_init_i2c(client, &isl12057_rtc_regmap_config);
 	if (IS_ERR(regmap)) {
 		ret = PTR_ERR(regmap);
 		dev_err(dev, "%s: regmap allocation failed (%d)\n",
 			__func__, ret);
 		return ret;
 	}

 	ret = isl12057_i2c_validate_chip(regmap);
 	if (ret)
 		return ret;

 	ret = isl12057_check_rtc_status(dev, regmap);
 	if (ret)
 		return ret;

 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;

 	mutex_init(&data->lock);
 	data->regmap = regmap;
 	dev_set_drvdata(dev, data);

 	rtc = devm_rtc_device_register(dev, DRV_NAME, &rtc_ops, THIS_MODULE);
 	return PTR_ERR_OR_ZERO(rtc);
 }

 #ifdef CONFIG_OF
 static const struct of_device_id isl12057_dt_match[] = {
 	{ .compatible = "isl,isl12057" },
 	{ },
 };
 #endif

 static const struct i2c_device_id isl12057_id[] = {
 	{ "isl12057", 0 },
 	{ }
 };
 MODULE_DEVICE_TABLE(i2c, isl12057_id);

 static struct i2c_driver isl12057_driver = {
 	.driver = {
 		.name = DRV_NAME,
 		.owner = THIS_MODULE,
 		.of_match_table = of_match_ptr(isl12057_dt_match),
 	},
 	.probe	  = isl12057_probe,
 	.id_table = isl12057_id,
 };
 module_i2c_driver(isl12057_driver);

 MODULE_AUTHOR("Arnaud EBALARD <arno@natisbad.org>");
 MODULE_DESCRIPTION("Intersil ISL12057 RTC driver");
 MODULE_LICENSE("GPL");
	/*
	* rtc-isl12057 - Driver for Intersil ISL12057 I2C Real Time Clock
	*
	* Copyright (C) 2013, Arnaud EBALARD <arno@natisbad.org>
	*
	* This work is largely based on Intersil ISL1208 driver developed by
	* Hebert Valerio Riedel <hvr@gnu.org>.
	*
	* Detailed datasheet on which this development is based is available here:
	*
	* http://natisbad.org/NAS2/refs/ISL12057.pdf
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*/

	#include <linux/module.h>
	#include <linux/mutex.h>
	#include <linux/rtc.h>
	#include <linux/i2c.h>
	#include <linux/bcd.h>
	#include <linux/of.h>
	#include <linux/of_device.h>
	#include <linux/regmap.h>

	#define DRV_NAME "rtc-isl12057"

	/* RTC section */
	#define ISL12057_REG_RTC_SC 0x00 /* Seconds */
	#define ISL12057_REG_RTC_MN 0x01 /* Minutes */
	#define ISL12057_REG_RTC_HR 0x02 /* Hours */
	#define ISL12057_REG_RTC_HR_PM BIT(5) /* AM/PM bit in 12h format */
	#define ISL12057_REG_RTC_HR_MIL BIT(6) /* 24h/12h format */
	#define ISL12057_REG_RTC_DW 0x03 /* Day of the Week */
	#define ISL12057_REG_RTC_DT 0x04 /* Date */
	#define ISL12057_REG_RTC_MO 0x05 /* Month */
	#define ISL12057_REG_RTC_MO_CEN BIT(7) /* Century bit */
	#define ISL12057_REG_RTC_YR 0x06 /* Year */
	#define ISL12057_RTC_SEC_LEN 7

	/* Alarm 1 section */
	#define ISL12057_REG_A1_SC 0x07 /* Alarm 1 Seconds */
	#define ISL12057_REG_A1_MN 0x08 /* Alarm 1 Minutes */
	#define ISL12057_REG_A1_HR 0x09 /* Alarm 1 Hours */
	#define ISL12057_REG_A1_HR_PM BIT(5) /* AM/PM bit in 12h format */
	#define ISL12057_REG_A1_HR_MIL BIT(6) /* 24h/12h format */
	#define ISL12057_REG_A1_DWDT 0x0A /* Alarm 1 Date / Day of the week */
	#define ISL12057_REG_A1_DWDT_B BIT(6) /* DW / DT selection bit */
	#define ISL12057_A1_SEC_LEN 4

	/* Alarm 2 section */
	#define ISL12057_REG_A2_MN 0x0B /* Alarm 2 Minutes */
	#define ISL12057_REG_A2_HR 0x0C /* Alarm 2 Hours */
	#define ISL12057_REG_A2_DWDT 0x0D /* Alarm 2 Date / Day of the week */
	#define ISL12057_A2_SEC_LEN 3

	/* Control/Status registers */
	#define ISL12057_REG_INT 0x0E
	#define ISL12057_REG_INT_A1IE BIT(0) /* Alarm 1 interrupt enable bit */
	#define ISL12057_REG_INT_A2IE BIT(1) /* Alarm 2 interrupt enable bit */
	#define ISL12057_REG_INT_INTCN BIT(2) /* Interrupt control enable bit */
	#define ISL12057_REG_INT_RS1 BIT(3) /* Freq out control bit 1 */
	#define ISL12057_REG_INT_RS2 BIT(4) /* Freq out control bit 2 */
	#define ISL12057_REG_INT_EOSC BIT(7) /* Oscillator enable bit */

	#define ISL12057_REG_SR 0x0F
	#define ISL12057_REG_SR_A1F BIT(0) /* Alarm 1 interrupt bit */
	#define ISL12057_REG_SR_A2F BIT(1) /* Alarm 2 interrupt bit */
	#define ISL12057_REG_SR_OSF BIT(7) /* Oscillator failure bit */

	/* Register memory map length */
	#define ISL12057_MEM_MAP_LEN 0x10

	struct isl12057_rtc_data {
	struct regmap *regmap;
	struct mutex lock;
	};

	static void isl12057_rtc_regs_to_tm(struct rtc_time tm, u8 regs)
	{
	tm->tm_sec = bcd2bin(regs[ISL12057_REG_RTC_SC]);
	tm->tm_min = bcd2bin(regs[ISL12057_REG_RTC_MN]);

	if (regs[ISL12057_REG_RTC_HR] & ISL12057_REG_RTC_HR_MIL) { /* AM/PM */
	tm->tm_hour = bcd2bin(regs[ISL12057_REG_RTC_HR] & 0x1f);
	if (regs[ISL12057_REG_RTC_HR] & ISL12057_REG_RTC_HR_PM)
	tm->tm_hour += 12;
	} else { /* 24 hour mode */
	tm->tm_hour = bcd2bin(regs[ISL12057_REG_RTC_HR] & 0x3f);
	}

	tm->tm_mday = bcd2bin(regs[ISL12057_REG_RTC_DT]);
	tm->tm_wday = bcd2bin(regs[ISL12057_REG_RTC_DW]) - 1; /* starts at 1 */
	tm->tm_mon = bcd2bin(regs[ISL12057_REG_RTC_MO] & 0x1f) - 1; /* ditto */
	tm->tm_year = bcd2bin(regs[ISL12057_REG_RTC_YR]) + 100;

	/* Check if years register has overflown from 99 to 00 */
	if (regs[ISL12057_REG_RTC_MO] & ISL12057_REG_RTC_MO_CEN)
	tm->tm_year += 100;
	}

	static int isl12057_rtc_tm_to_regs(u8 regs, struct rtc_time tm)
	{
	u8 century_bit;

	/*
	* The clock has an 8 bit wide bcd-coded register for the year.
	* It also has a century bit encoded in MO flag which provides
	* information about overflow of year register from 99 to 00.
	* tm_year is an offset from 1900 and we are interested in the
	* 2000-2199 range, so any value less than 100 or larger than
	* 299 is invalid.
	*/
	if (tm->tm_year < 100 \|\| tm->tm_year > 299)
	return -EINVAL;

	century_bit = (tm->tm_year > 199) ? ISL12057_REG_RTC_MO_CEN : 0;

	regs[ISL12057_REG_RTC_SC] = bin2bcd(tm->tm_sec);
	regs[ISL12057_REG_RTC_MN] = bin2bcd(tm->tm_min);
	regs[ISL12057_REG_RTC_HR] = bin2bcd(tm->tm_hour); /* 24-hour format */
	regs[ISL12057_REG_RTC_DT] = bin2bcd(tm->tm_mday);
	regs[ISL12057_REG_RTC_MO] = bin2bcd(tm->tm_mon + 1) \| century_bit;
	regs[ISL12057_REG_RTC_YR] = bin2bcd(tm->tm_year % 100);
	regs[ISL12057_REG_RTC_DW] = bin2bcd(tm->tm_wday + 1);

	return 0;
	}

	/*
	* Try and match register bits w/ fixed null values to see whether we
	* are dealing with an ISL12057. Note: this function is called early
	* during init and hence does need mutex protection.
	*/
	static int isl12057_i2c_validate_chip(struct regmap *regmap)
	{
	u8 regs[ISL12057_MEM_MAP_LEN];
	static const u8 mask[ISL12057_MEM_MAP_LEN] = { 0x80, 0x80, 0x80, 0xf8,
	0xc0, 0x60, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x60, 0x7c };
	int ret, i;

	ret = regmap_bulk_read(regmap, 0, regs, ISL12057_MEM_MAP_LEN);
	if (ret)
	return ret;

	for (i = 0; i < ISL12057_MEM_MAP_LEN; ++i) {
	if (regs[i] & mask[i]) /* check if bits are cleared */
	return -ENODEV;
	}

	return 0;
	}

	static int isl12057_rtc_read_time(struct device dev, struct rtc_time tm)
	{
	struct isl12057_rtc_data *data = dev_get_drvdata(dev);
	u8 regs[ISL12057_RTC_SEC_LEN];
	unsigned int sr;
	int ret;

	mutex_lock(&data->lock);
	ret = regmap_read(data->regmap, ISL12057_REG_SR, &sr);
	if (ret) {
	dev_err(dev, "%s: unable to read oscillator status flag (%d)\n",
	__func__, ret);
	goto out;
	} else {
	if (sr & ISL12057_REG_SR_OSF) {
	ret = -ENODATA;
	goto out;
	}
	}

	ret = regmap_bulk_read(data->regmap, ISL12057_REG_RTC_SC, regs,
	ISL12057_RTC_SEC_LEN);
	if (ret)
	dev_err(dev, "%s: unable to read RTC time section (%d)\n",
	__func__, ret);

	out:
	mutex_unlock(&data->lock);

	if (ret)
	return ret;

	isl12057_rtc_regs_to_tm(tm, regs);

	return rtc_valid_tm(tm);
	}

	static int isl12057_rtc_set_time(struct device dev, struct rtc_time tm)
	{
	struct isl12057_rtc_data *data = dev_get_drvdata(dev);
	u8 regs[ISL12057_RTC_SEC_LEN];
	int ret;

	ret = isl12057_rtc_tm_to_regs(regs, tm);
	if (ret)
	return ret;

	mutex_lock(&data->lock);
	ret = regmap_bulk_write(data->regmap, ISL12057_REG_RTC_SC, regs,
	ISL12057_RTC_SEC_LEN);
	if (ret) {
	dev_err(dev, "%s: unable to write RTC time section (%d)\n",
	__func__, ret);
	goto out;
	}

	/*
	* Now that RTC time has been updated, let's clear oscillator
	* failure flag, if needed.
	*/
	ret = regmap_update_bits(data->regmap, ISL12057_REG_SR,
	ISL12057_REG_SR_OSF, 0);
	if (ret < 0)
	dev_err(dev, "%s: unable to clear osc. failure bit (%d)\n",
	__func__, ret);

	out:
	mutex_unlock(&data->lock);

	return ret;
	}

	/*
	* Check current RTC status and enable/disable what needs to be. Return 0 if
	* everything went ok and a negative value upon error. Note: this function
	* is called early during init and hence does need mutex protection.
	*/
	static int isl12057_check_rtc_status(struct device dev, struct regmap regmap)
	{
	int ret;

	/* Enable oscillator if not already running */
	ret = regmap_update_bits(regmap, ISL12057_REG_INT,
	ISL12057_REG_INT_EOSC, 0);
	if (ret < 0) {
	dev_err(dev, "%s: unable to enable oscillator (%d)\n",
	__func__, ret);
	return ret;
	}

	/* Clear alarm bit if needed */
	ret = regmap_update_bits(regmap, ISL12057_REG_SR,
	ISL12057_REG_SR_A1F, 0);
	if (ret < 0) {
	dev_err(dev, "%s: unable to clear alarm bit (%d)\n",
	__func__, ret);
	return ret;
	}

	return 0;
	}

	static const struct rtc_class_ops rtc_ops = {
	.read_time = isl12057_rtc_read_time,
	.set_time = isl12057_rtc_set_time,
	};

	static struct regmap_config isl12057_rtc_regmap_config = {
	.reg_bits = 8,
	.val_bits = 8,
	};

	static int isl12057_probe(struct i2c_client *client,
	const struct i2c_device_id *id)
	{
	struct device *dev = &client->dev;
	struct isl12057_rtc_data *data;
	struct rtc_device *rtc;
	struct regmap *regmap;
	int ret;

	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C \|
	I2C_FUNC_SMBUS_BYTE_DATA \|
	I2C_FUNC_SMBUS_I2C_BLOCK))
	return -ENODEV;

	regmap = devm_regmap_init_i2c(client, &isl12057_rtc_regmap_config);
	if (IS_ERR(regmap)) {
	ret = PTR_ERR(regmap);
	dev_err(dev, "%s: regmap allocation failed (%d)\n",
	__func__, ret);
	return ret;
	}

	ret = isl12057_i2c_validate_chip(regmap);
	if (ret)
	return ret;

	ret = isl12057_check_rtc_status(dev, regmap);
	if (ret)
	return ret;

	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
	if (!data)
	return -ENOMEM;

	mutex_init(&data->lock);
	data->regmap = regmap;
	dev_set_drvdata(dev, data);

	rtc = devm_rtc_device_register(dev, DRV_NAME, &rtc_ops, THIS_MODULE);
	return PTR_ERR_OR_ZERO(rtc);
	}

	#ifdef CONFIG_OF
	static const struct of_device_id isl12057_dt_match[] = {
	{ .compatible = "isl,isl12057" },
	{ },
	};
	#endif

	static const struct i2c_device_id isl12057_id[] = {
	{ "isl12057", 0 },
	{ }
	};
	MODULE_DEVICE_TABLE(i2c, isl12057_id);

	static struct i2c_driver isl12057_driver = {
	.driver = {
	.name = DRV_NAME,
	.owner = THIS_MODULE,
	.of_match_table = of_match_ptr(isl12057_dt_match),
	},
	.probe = isl12057_probe,
	.id_table = isl12057_id,
	};
	module_i2c_driver(isl12057_driver);

	MODULE_AUTHOR("Arnaud EBALARD <arno@natisbad.org>");
	MODULE_DESCRIPTION("Intersil ISL12057 RTC driver");
	MODULE_LICENSE("GPL");