/*
   * rtc class driver for the Maxim MAX6900 chip
   *
   * Author: Dale Farnsworth <dale@farnsworth.org>
   *
   * based on previously existing rtc class drivers
   *
   * 2007 (c) MontaVista, Software, Inc.  This file is licensed under
   * the terms of the GNU General Public License version 2.  This program
   * is licensed "as is" without any warranty of any kind, whether express
   * or implied.
   */
  
  #include <linux/module.h>
  #include <linux/i2c.h>
  #include <linux/bcd.h>
  #include <linux/rtc.h>
  #include <linux/delay.h>
  
  #define DRV_VERSION "0.2"
  
  /*
   * register indices
   */
  #define MAX6900_REG_SC			0	/* seconds      00-59 */
  #define MAX6900_REG_MN			1	/* minutes      00-59 */
  #define MAX6900_REG_HR			2	/* hours        00-23 */
  #define MAX6900_REG_DT			3	/* day of month 00-31 */
  #define MAX6900_REG_MO			4	/* month        01-12 */
  #define MAX6900_REG_DW			5	/* day of week   1-7  */
  #define MAX6900_REG_YR			6	/* year         00-99 */
  #define MAX6900_REG_CT			7	/* control */
  						/* register 8 is undocumented */
  #define MAX6900_REG_CENTURY		9	/* century */
  #define MAX6900_REG_LEN			10
  
  #define MAX6900_BURST_LEN		8	/* can burst r/w first 8 regs */
  
  #define MAX6900_REG_CT_WP		(1 << 7)	/* Write Protect */
  
  /*
   * register read/write commands
   */
  #define MAX6900_REG_CONTROL_WRITE	0x8e
  #define MAX6900_REG_CENTURY_WRITE	0x92
  #define MAX6900_REG_CENTURY_READ	0x93
  #define MAX6900_REG_RESERVED_READ	0x96
  #define MAX6900_REG_BURST_WRITE		0xbe
  #define MAX6900_REG_BURST_READ		0xbf
  
  #define MAX6900_IDLE_TIME_AFTER_WRITE	3	/* specification says 2.5 mS */
  
  static struct i2c_driver max6900_driver;
  
  static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
  {
  	u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
  	u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
  	struct i2c_msg msgs[4] = {
  		{
  		 .addr = client->addr,
  		 .flags = 0,	/* write */
  		 .len = sizeof(reg_burst_read),
  		 .buf = reg_burst_read}
  		,
  		{
  		 .addr = client->addr,
  		 .flags = I2C_M_RD,
  		 .len = MAX6900_BURST_LEN,
  		 .buf = buf}
  		,
  		{
  		 .addr = client->addr,
  		 .flags = 0,	/* write */
  		 .len = sizeof(reg_century_read),
  		 .buf = reg_century_read}
  		,
  		{
  		 .addr = client->addr,
  		 .flags = I2C_M_RD,
  		 .len = sizeof(buf[MAX6900_REG_CENTURY]),
  		 .buf = &buf[MAX6900_REG_CENTURY]
  		 }
  	};
  	int rc;
  
  	rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
  	if (rc != ARRAY_SIZE(msgs)) {
  		dev_err(&client->dev, "%s: register read failed
  ", __func__);
  		return -EIO;
  	}
  	return 0;
  }
  
  static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
  {
  	u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
  	struct i2c_msg century_msgs[1] = {
  		{
  		 .addr = client->addr,
  		 .flags = 0,	/* write */
  		 .len = sizeof(i2c_century_buf),
  		 .buf = i2c_century_buf}
  	};
  	u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
  	struct i2c_msg burst_msgs[1] = {
  		{
  		 .addr = client->addr,
  		 .flags = 0,	/* write */
  		 .len = sizeof(i2c_burst_buf),
  		 .buf = i2c_burst_buf}
  	};
  	int rc;
  
  	/*
  	 * We have to make separate calls to i2c_transfer because of
  	 * the need to delay after each write to the chip.  Also,
  	 * we write the century byte first, since we set the write-protect
  	 * bit as part of the burst write.
  	 */
  	i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];
  
  	rc = i2c_transfer(client->adapter, century_msgs,
  			  ARRAY_SIZE(century_msgs));
  	if (rc != ARRAY_SIZE(century_msgs))
  		goto write_failed;
  
  	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
  
  	memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);
  
  	rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
  	if (rc != ARRAY_SIZE(burst_msgs))
  		goto write_failed;
  	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
  
  	return 0;
  
   write_failed:
  	dev_err(&client->dev, "%s: register write failed
  ", __func__);
  	return -EIO;
  }
  
  static int max6900_i2c_read_time(struct i2c_client *client, struct rtc_time *tm)
  {
  	int rc;
  	u8 regs[MAX6900_REG_LEN];
  
  	rc = max6900_i2c_read_regs(client, regs);
  	if (rc < 0)
  		return rc;
  
  	tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
  	tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
  	tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
  	tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
  	tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
  	tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
  		      bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
  	tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);
  
  	return rtc_valid_tm(tm);
  }
  
  static int max6900_i2c_clear_write_protect(struct i2c_client *client)
  {
  	return i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
  }
  
  static int
  max6900_i2c_set_time(struct i2c_client *client, struct rtc_time const *tm)
  {
  	u8 regs[MAX6900_REG_LEN];
  	int rc;
  
  	rc = max6900_i2c_clear_write_protect(client);
  	if (rc < 0)
  		return rc;
  
  	regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
  	regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
  	regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
  	regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
  	regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
  	regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
  	regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
  	regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
  	/* set write protect */
  	regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;
  
  	rc = max6900_i2c_write_regs(client, regs);
  	if (rc < 0)
  		return rc;
  
  	return 0;
  }
  
  static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
  {
  	return max6900_i2c_read_time(to_i2c_client(dev), tm);
  }
  
  static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
  {
  	return max6900_i2c_set_time(to_i2c_client(dev), tm);
  }
  
  static const struct rtc_class_ops max6900_rtc_ops = {
  	.read_time = max6900_rtc_read_time,
  	.set_time = max6900_rtc_set_time,
  };
  
  static int
  max6900_probe(struct i2c_client *client, const struct i2c_device_id *id)
  {
  	struct rtc_device *rtc;
  
  	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
  		return -ENODEV;
  
  	dev_info(&client->dev, "chip found, driver version " DRV_VERSION "
  ");
  
  	rtc = devm_rtc_device_register(&client->dev, max6900_driver.driver.name,
  					&max6900_rtc_ops, THIS_MODULE);
  	if (IS_ERR(rtc))
  		return PTR_ERR(rtc);
  
  	i2c_set_clientdata(client, rtc);
  
  	return 0;
  }
  
  static struct i2c_device_id max6900_id[] = {
  	{ "max6900", 0 },
  	{ }
  };
  
  static struct i2c_driver max6900_driver = {
  	.driver = {
  		   .name = "rtc-max6900",
  		   },
  	.probe = max6900_probe,
  	.id_table = max6900_id,
  };
  
  module_i2c_driver(max6900_driver);
  
  MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
  MODULE_AUTHOR("Dale Farnsworth <dale@farnsworth.org>");
  MODULE_LICENSE("GPL");
  MODULE_VERSION(DRV_VERSION);