// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Dallas DS1302 RTC Support
   *

   *  Copyright (C) 2002 David McCullough
   *  Copyright (C) 2003 - 2007 Paul Mundt

   */

  #include <linux/bcd.h>

  #include <linux/init.h>

  #include <linux/io.h>

  #include <linux/kernel.h>

  #include <linux/module.h>
  #include <linux/of.h>

  #include <linux/rtc.h>

  #include <linux/spi/spi.h>

  #define	RTC_CMD_READ	0x81		/* Read command */
  #define	RTC_CMD_WRITE	0x80		/* Write command */

  #define	RTC_CMD_WRITE_ENABLE	0x00		/* Write enable */
  #define	RTC_CMD_WRITE_DISABLE	0x80		/* Write disable */

  #define RTC_ADDR_RAM0	0x20		/* Address of RAM0 */
  #define RTC_ADDR_TCR	0x08		/* Address of trickle charge register */

  #define RTC_CLCK_BURST	0x1F		/* Address of clock burst */
  #define	RTC_CLCK_LEN	0x08		/* Size of clock burst */

  #define	RTC_ADDR_CTRL	0x07		/* Address of control register */

  #define	RTC_ADDR_YEAR	0x06		/* Address of year register */
  #define	RTC_ADDR_DAY	0x05		/* Address of day of week register */
  #define	RTC_ADDR_MON	0x04		/* Address of month register */
  #define	RTC_ADDR_DATE	0x03		/* Address of day of month register */
  #define	RTC_ADDR_HOUR	0x02		/* Address of hour register */
  #define	RTC_ADDR_MIN	0x01		/* Address of minute register */
  #define	RTC_ADDR_SEC	0x00		/* Address of second register */

  static int ds1302_rtc_set_time(struct device *dev, struct rtc_time *time)

  {

  	struct spi_device	*spi = dev_get_drvdata(dev);
  	u8		buf[1 + RTC_CLCK_LEN];

  	u8		*bp;

  	int		status;
  
  	/* Enable writing */
  	bp = buf;
  	*bp++ = RTC_ADDR_CTRL << 1 | RTC_CMD_WRITE;
  	*bp++ = RTC_CMD_WRITE_ENABLE;
  
  	status = spi_write_then_read(spi, buf, 2,
  			NULL, 0);

  	if (status)

  		return status;
  
  	/* Write registers starting at the first time/date address. */
  	bp = buf;
  	*bp++ = RTC_CLCK_BURST << 1 | RTC_CMD_WRITE;
  
  	*bp++ = bin2bcd(time->tm_sec);
  	*bp++ = bin2bcd(time->tm_min);
  	*bp++ = bin2bcd(time->tm_hour);
  	*bp++ = bin2bcd(time->tm_mday);
  	*bp++ = bin2bcd(time->tm_mon + 1);

  	*bp++ = time->tm_wday + 1;

  	*bp++ = bin2bcd(time->tm_year % 100);
  	*bp++ = RTC_CMD_WRITE_DISABLE;
  
  	/* use write-then-read since dma from stack is nonportable */
  	return spi_write_then_read(spi, buf, sizeof(buf),
  			NULL, 0);

  }

  static int ds1302_rtc_get_time(struct device *dev, struct rtc_time *time)

  {

  	struct spi_device	*spi = dev_get_drvdata(dev);
  	u8		addr = RTC_CLCK_BURST << 1 | RTC_CMD_READ;
  	u8		buf[RTC_CLCK_LEN - 1];
  	int		status;
  
  	/* Use write-then-read to get all the date/time registers
  	 * since dma from stack is nonportable
  	 */
  	status = spi_write_then_read(spi, &addr, sizeof(addr),
  			buf, sizeof(buf));
  	if (status < 0)
  		return status;
  
  	/* Decode the registers */
  	time->tm_sec = bcd2bin(buf[RTC_ADDR_SEC]);
  	time->tm_min = bcd2bin(buf[RTC_ADDR_MIN]);
  	time->tm_hour = bcd2bin(buf[RTC_ADDR_HOUR]);
  	time->tm_wday = buf[RTC_ADDR_DAY] - 1;
  	time->tm_mday = bcd2bin(buf[RTC_ADDR_DATE]);
  	time->tm_mon = bcd2bin(buf[RTC_ADDR_MON]) - 1;
  	time->tm_year = bcd2bin(buf[RTC_ADDR_YEAR]) + 100;

  	return 0;

  }

  static const struct rtc_class_ops ds1302_rtc_ops = {

  	.read_time	= ds1302_rtc_get_time,
  	.set_time	= ds1302_rtc_set_time,
  };

  static int ds1302_probe(struct spi_device *spi)

  {

  	struct rtc_device	*rtc;
  	u8		addr;
  	u8		buf[4];

  	u8		*bp;

  	int		status;
  
  	/* Sanity check board setup data.  This may be hooked up
  	 * in 3wire mode, but we don't care.  Note that unless
  	 * there's an inverter in place, this needs SPI_CS_HIGH!
  	 */
  	if (spi->bits_per_word && (spi->bits_per_word != 8)) {
  		dev_err(&spi->dev, "bad word length
  ");
  		return -EINVAL;
  	} else if (spi->max_speed_hz > 2000000) {
  		dev_err(&spi->dev, "speed is too high
  ");
  		return -EINVAL;
  	} else if (spi->mode & SPI_CPHA) {
  		dev_err(&spi->dev, "bad mode
  ");
  		return -EINVAL;

  	}

  	addr = RTC_ADDR_CTRL << 1 | RTC_CMD_READ;
  	status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
  	if (status < 0) {
  		dev_err(&spi->dev, "control register read error %d
  ",
  				status);
  		return status;

  	}

  	if ((buf[0] & ~RTC_CMD_WRITE_DISABLE) != 0) {
  		status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
  		if (status < 0) {
  			dev_err(&spi->dev, "control register read error %d
  ",
  					status);
  			return status;
  		}
  
  		if ((buf[0] & ~RTC_CMD_WRITE_DISABLE) != 0) {
  			dev_err(&spi->dev, "junk in control register
  ");
  			return -ENODEV;
  		}
  	}
  	if (buf[0] == 0) {
  		bp = buf;
  		*bp++ = RTC_ADDR_CTRL << 1 | RTC_CMD_WRITE;
  		*bp++ = RTC_CMD_WRITE_DISABLE;
  
  		status = spi_write_then_read(spi, buf, 2, NULL, 0);
  		if (status < 0) {
  			dev_err(&spi->dev, "control register write error %d
  ",
  					status);
  			return status;
  		}
  
  		addr = RTC_ADDR_CTRL << 1 | RTC_CMD_READ;
  		status = spi_write_then_read(spi, &addr, sizeof(addr), buf, 1);
  		if (status < 0) {
  			dev_err(&spi->dev,
  					"error %d reading control register
  ",
  					status);
  			return status;
  		}
  
  		if (buf[0] != RTC_CMD_WRITE_DISABLE) {
  			dev_err(&spi->dev, "failed to detect chip
  ");
  			return -ENODEV;
  		}
  	}

  	spi_set_drvdata(spi, spi);

  	rtc = devm_rtc_device_register(&spi->dev, "ds1302",
  			&ds1302_rtc_ops, THIS_MODULE);
  	if (IS_ERR(rtc)) {
  		status = PTR_ERR(rtc);
  		dev_err(&spi->dev, "error %d registering rtc
  ", status);
  		return status;
  	}

  	return 0;
  }

  static int ds1302_remove(struct spi_device *spi)

  {

  	spi_set_drvdata(spi, NULL);
  	return 0;

  }

  #ifdef CONFIG_OF
  static const struct of_device_id ds1302_dt_ids[] = {
  	{ .compatible = "maxim,ds1302", },
  	{ /* sentinel */ }

  };

  MODULE_DEVICE_TABLE(of, ds1302_dt_ids);
  #endif

  static struct spi_driver ds1302_driver = {
  	.driver.name	= "rtc-ds1302",
  	.driver.of_match_table = of_match_ptr(ds1302_dt_ids),
  	.probe		= ds1302_probe,
  	.remove		= ds1302_remove,

  };

  module_spi_driver(ds1302_driver);

  
  MODULE_DESCRIPTION("Dallas DS1302 RTC driver");

  MODULE_AUTHOR("Paul Mundt, David McCullough");
  MODULE_LICENSE("GPL v2");