/*
   * Copyright (C) 2012 Avionic Design 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/bcd.h>
  #include <linux/i2c.h>
  #include <linux/module.h>
  #include <linux/rtc.h>
  #include <linux/of.h>
  
  #define DRIVER_NAME "rtc-pcf8523"
  
  #define REG_CONTROL1 0x00
  #define REG_CONTROL1_CAP_SEL (1 << 7)
  #define REG_CONTROL1_STOP    (1 << 5)
  
  #define REG_CONTROL3 0x02
  #define REG_CONTROL3_PM_BLD (1 << 7) /* battery low detection disabled */
  #define REG_CONTROL3_PM_VDD (1 << 6) /* switch-over disabled */
  #define REG_CONTROL3_PM_DSM (1 << 5) /* direct switching mode */
  #define REG_CONTROL3_PM_MASK 0xe0
  #define REG_CONTROL3_BLF (1 << 2) /* battery low bit, read-only */
  
  #define REG_SECONDS  0x03
  #define REG_SECONDS_OS (1 << 7)
  
  #define REG_MINUTES  0x04
  #define REG_HOURS    0x05
  #define REG_DAYS     0x06
  #define REG_WEEKDAYS 0x07
  #define REG_MONTHS   0x08
  #define REG_YEARS    0x09
  
  struct pcf8523 {
  	struct rtc_device *rtc;
  };
  
  static int pcf8523_read(struct i2c_client *client, u8 reg, u8 *valuep)
  {
  	struct i2c_msg msgs[2];
  	u8 value = 0;
  	int err;
  
  	msgs[0].addr = client->addr;
  	msgs[0].flags = 0;
  	msgs[0].len = sizeof(reg);
  	msgs[0].buf = &reg;
  
  	msgs[1].addr = client->addr;
  	msgs[1].flags = I2C_M_RD;
  	msgs[1].len = sizeof(value);
  	msgs[1].buf = &value;
  
  	err = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
  	if (err < 0)
  		return err;
  
  	*valuep = value;
  
  	return 0;
  }
  
  static int pcf8523_write(struct i2c_client *client, u8 reg, u8 value)
  {
  	u8 buffer[2] = { reg, value };
  	struct i2c_msg msg;
  	int err;
  
  	msg.addr = client->addr;
  	msg.flags = 0;
  	msg.len = sizeof(buffer);
  	msg.buf = buffer;
  
  	err = i2c_transfer(client->adapter, &msg, 1);
  	if (err < 0)
  		return err;
  
  	return 0;
  }
  
  static int pcf8523_select_capacitance(struct i2c_client *client, bool high)
  {
  	u8 value;
  	int err;
  
  	err = pcf8523_read(client, REG_CONTROL1, &value);
  	if (err < 0)
  		return err;
  
  	if (!high)
  		value &= ~REG_CONTROL1_CAP_SEL;
  	else
  		value |= REG_CONTROL1_CAP_SEL;
  
  	err = pcf8523_write(client, REG_CONTROL1, value);
  	if (err < 0)
  		return err;
  
  	return err;
  }
  
  static int pcf8523_set_pm(struct i2c_client *client, u8 pm)
  {
  	u8 value;
  	int err;
  
  	err = pcf8523_read(client, REG_CONTROL3, &value);
  	if (err < 0)
  		return err;
  
  	value = (value & ~REG_CONTROL3_PM_MASK) | pm;
  
  	err = pcf8523_write(client, REG_CONTROL3, value);
  	if (err < 0)
  		return err;
  
  	return 0;
  }
  
  static int pcf8523_stop_rtc(struct i2c_client *client)
  {
  	u8 value;
  	int err;
  
  	err = pcf8523_read(client, REG_CONTROL1, &value);
  	if (err < 0)
  		return err;
  
  	value |= REG_CONTROL1_STOP;
  
  	err = pcf8523_write(client, REG_CONTROL1, value);
  	if (err < 0)
  		return err;
  
  	return 0;
  }
  
  static int pcf8523_start_rtc(struct i2c_client *client)
  {
  	u8 value;
  	int err;
  
  	err = pcf8523_read(client, REG_CONTROL1, &value);
  	if (err < 0)
  		return err;
  
  	value &= ~REG_CONTROL1_STOP;
  
  	err = pcf8523_write(client, REG_CONTROL1, value);
  	if (err < 0)
  		return err;
  
  	return 0;
  }
  
  static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	u8 start = REG_SECONDS, regs[7];
  	struct i2c_msg msgs[2];
  	int err;
  
  	msgs[0].addr = client->addr;
  	msgs[0].flags = 0;
  	msgs[0].len = 1;
  	msgs[0].buf = &start;
  
  	msgs[1].addr = client->addr;
  	msgs[1].flags = I2C_M_RD;
  	msgs[1].len = sizeof(regs);
  	msgs[1].buf = regs;
  
  	err = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
  	if (err < 0)
  		return err;
  
  	if (regs[0] & REG_SECONDS_OS) {
  		/*
  		 * If the oscillator was stopped, try to clear the flag. Upon
  		 * power-up the flag is always set, but if we cannot clear it
  		 * the oscillator isn't running properly for some reason. The
  		 * sensible thing therefore is to return an error, signalling
  		 * that the clock cannot be assumed to be correct.
  		 */
  
  		regs[0] &= ~REG_SECONDS_OS;
  
  		err = pcf8523_write(client, REG_SECONDS, regs[0]);
  		if (err < 0)
  			return err;
  
  		err = pcf8523_read(client, REG_SECONDS, &regs[0]);
  		if (err < 0)
  			return err;
  
  		if (regs[0] & REG_SECONDS_OS)
  			return -EAGAIN;
  	}
  
  	tm->tm_sec = bcd2bin(regs[0] & 0x7f);
  	tm->tm_min = bcd2bin(regs[1] & 0x7f);
  	tm->tm_hour = bcd2bin(regs[2] & 0x3f);
  	tm->tm_mday = bcd2bin(regs[3] & 0x3f);
  	tm->tm_wday = regs[4] & 0x7;
  	tm->tm_mon = bcd2bin(regs[5] & 0x1f);
  	tm->tm_year = bcd2bin(regs[6]) + 100;
  
  	return rtc_valid_tm(tm);
  }
  
  static int pcf8523_rtc_set_time(struct device *dev, struct rtc_time *tm)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	struct i2c_msg msg;
  	u8 regs[8];
  	int err;
  
  	err = pcf8523_stop_rtc(client);
  	if (err < 0)
  		return err;
  
  	regs[0] = REG_SECONDS;
  	regs[1] = bin2bcd(tm->tm_sec);
  	regs[2] = bin2bcd(tm->tm_min);
  	regs[3] = bin2bcd(tm->tm_hour);
  	regs[4] = bin2bcd(tm->tm_mday);
  	regs[5] = tm->tm_wday;
  	regs[6] = bin2bcd(tm->tm_mon);
  	regs[7] = bin2bcd(tm->tm_year - 100);
  
  	msg.addr = client->addr;
  	msg.flags = 0;
  	msg.len = sizeof(regs);
  	msg.buf = regs;
  
  	err = i2c_transfer(client->adapter, &msg, 1);
  	if (err < 0) {
  		/*
  		 * If the time cannot be set, restart the RTC anyway. Note
  		 * that errors are ignored if the RTC cannot be started so
  		 * that we have a chance to propagate the original error.
  		 */
  		pcf8523_start_rtc(client);
  		return err;
  	}
  
  	return pcf8523_start_rtc(client);
  }
  
  #ifdef CONFIG_RTC_INTF_DEV
  static int pcf8523_rtc_ioctl(struct device *dev, unsigned int cmd,
  			     unsigned long arg)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	u8 value;
  	int ret = 0, err;
  
  	switch (cmd) {
  	case RTC_VL_READ:
  		err = pcf8523_read(client, REG_CONTROL3, &value);
  		if (err < 0)
  			return err;
  
  		if (value & REG_CONTROL3_BLF)
  			ret = 1;
  
  		if (copy_to_user((void __user *)arg, &ret, sizeof(int)))
  			return -EFAULT;
  
  		return 0;
  	default:
  		return -ENOIOCTLCMD;
  	}
  }
  #else
  #define pcf8523_rtc_ioctl NULL
  #endif
  
  static const struct rtc_class_ops pcf8523_rtc_ops = {
  	.read_time = pcf8523_rtc_read_time,
  	.set_time = pcf8523_rtc_set_time,
  	.ioctl = pcf8523_rtc_ioctl,
  };
  
  static int pcf8523_probe(struct i2c_client *client,
  			 const struct i2c_device_id *id)
  {
  	struct pcf8523 *pcf;
  	int err;
  
  	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
  		return -ENODEV;
  
  	pcf = devm_kzalloc(&client->dev, sizeof(*pcf), GFP_KERNEL);
  	if (!pcf)
  		return -ENOMEM;
  
  	err = pcf8523_select_capacitance(client, true);
  	if (err < 0)
  		return err;
  
  	err = pcf8523_set_pm(client, 0);
  	if (err < 0)
  		return err;
  
  	pcf->rtc = devm_rtc_device_register(&client->dev, DRIVER_NAME,
  				       &pcf8523_rtc_ops, THIS_MODULE);
  	if (IS_ERR(pcf->rtc))
  		return PTR_ERR(pcf->rtc);
  
  	i2c_set_clientdata(client, pcf);
  
  	return 0;
  }
  
  static const struct i2c_device_id pcf8523_id[] = {
  	{ "pcf8523", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, pcf8523_id);
  
  #ifdef CONFIG_OF
  static const struct of_device_id pcf8523_of_match[] = {
  	{ .compatible = "nxp,pcf8523" },
  	{ }
  };
  MODULE_DEVICE_TABLE(of, pcf8523_of_match);
  #endif
  
  static struct i2c_driver pcf8523_driver = {
  	.driver = {
  		.name = DRIVER_NAME,
  		.owner = THIS_MODULE,
  		.of_match_table = of_match_ptr(pcf8523_of_match),
  	},
  	.probe = pcf8523_probe,
  	.id_table = pcf8523_id,
  };
  module_i2c_driver(pcf8523_driver);
  
  MODULE_AUTHOR("Thierry Reding <thierry.reding@avionic-design.de>");
  MODULE_DESCRIPTION("NXP PCF8523 RTC driver");
  MODULE_LICENSE("GPL v2");