/* rtc-ds1347.c
 *
 * Driver for Dallas Semiconductor DS1347 Low Current, SPI Compatible
 * Real Time Clock
 *
 * Author : Raghavendra Chandra Ganiga <ravi23ganiga@gmail.com>
 *
 * 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/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/rtc.h>
#include <linux/spi/spi.h>
#include <linux/bcd.h>

/* Registers in ds1347 rtc */

#define DS1347_SECONDS_REG	0x01
#define DS1347_MINUTES_REG	0x03
#define DS1347_HOURS_REG	0x05
#define DS1347_DATE_REG		0x07
#define DS1347_MONTH_REG	0x09
#define DS1347_DAY_REG		0x0B
#define DS1347_YEAR_REG		0x0D
#define DS1347_CONTROL_REG	0x0F
#define DS1347_STATUS_REG	0x17
#define DS1347_CLOCK_BURST	0x3F

static int ds1347_read_reg(struct device *dev, unsigned char address,
				unsigned char *data)
{
	struct spi_device *spi = to_spi_device(dev);

	*data = address | 0x80;

	return spi_write_then_read(spi, data, 1, data, 1);
}

static int ds1347_write_reg(struct device *dev, unsigned char address,
				unsigned char data)
{
	struct spi_device *spi = to_spi_device(dev);
	unsigned char buf[2];

	buf[0] = address & 0x7F;
	buf[1] = data;

	return spi_write_then_read(spi, buf, 2, NULL, 0);
}

static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
{
	struct spi_device *spi = to_spi_device(dev);
	int err;
	unsigned char buf[8];

	buf[0] = DS1347_CLOCK_BURST | 0x80;

	err = spi_write_then_read(spi, buf, 1, buf, 8);
	if (err)
		return err;

	dt->tm_sec = bcd2bin(buf[0]);
	dt->tm_min = bcd2bin(buf[1]);
	dt->tm_hour = bcd2bin(buf[2] & 0x3F);
	dt->tm_mday = bcd2bin(buf[3]);
	dt->tm_mon = bcd2bin(buf[4]) - 1;
	dt->tm_wday = bcd2bin(buf[5]) - 1;
	dt->tm_year = bcd2bin(buf[6]) + 100;

	return rtc_valid_tm(dt);
}

static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
{
	struct spi_device *spi = to_spi_device(dev);
	unsigned char buf[9];

	buf[0] = DS1347_CLOCK_BURST & 0x7F;
	buf[1] = bin2bcd(dt->tm_sec);
	buf[2] = bin2bcd(dt->tm_min);
	buf[3] = (bin2bcd(dt->tm_hour) & 0x3F);
	buf[4] = bin2bcd(dt->tm_mday);
	buf[5] = bin2bcd(dt->tm_mon + 1);
	buf[6] = bin2bcd(dt->tm_wday + 1);

	/* year in linux is from 1900 i.e in range of 100
	in rtc it is from 00 to 99 */
	dt->tm_year = dt->tm_year % 100;

	buf[7] = bin2bcd(dt->tm_year);
	buf[8] = bin2bcd(0x00);

	/* write the rtc settings */
	return spi_write_then_read(spi, buf, 9, NULL, 0);
}

static const struct rtc_class_ops ds1347_rtc_ops = {
	.read_time = ds1347_read_time,
	.set_time = ds1347_set_time,
};

static int ds1347_probe(struct spi_device *spi)
{
	struct rtc_device *rtc;
	unsigned char data;
	int res;

	/* spi setup with ds1347 in mode 3 and bits per word as 8 */
	spi->mode = SPI_MODE_3;
	spi->bits_per_word = 8;
	spi_setup(spi);

	/* RTC Settings */
	res = ds1347_read_reg(&spi->dev, DS1347_SECONDS_REG, &data);
	if (res)
		return res;

	/* Disable the write protect of rtc */
	ds1347_read_reg(&spi->dev, DS1347_CONTROL_REG, &data);
	data = data & ~(1<<7);
	ds1347_write_reg(&spi->dev, DS1347_CONTROL_REG, data);

	/* Enable the oscillator , disable the oscillator stop flag,
	 and glitch filter to reduce current consumption */
	ds1347_read_reg(&spi->dev, DS1347_STATUS_REG, &data);
	data = data & 0x1B;
	ds1347_write_reg(&spi->dev, DS1347_STATUS_REG, data);

	/* display the settings */
	ds1347_read_reg(&spi->dev, DS1347_CONTROL_REG, &data);
	dev_info(&spi->dev, "DS1347 RTC CTRL Reg = 0x%02x\n", data);

	ds1347_read_reg(&spi->dev, DS1347_STATUS_REG, &data);
	dev_info(&spi->dev, "DS1347 RTC Status Reg = 0x%02x\n", data);

	rtc = devm_rtc_device_register(&spi->dev, "ds1347",
				&ds1347_rtc_ops, THIS_MODULE);

	if (IS_ERR(rtc))
		return PTR_ERR(rtc);

	spi_set_drvdata(spi, rtc);

	return 0;
}

static struct spi_driver ds1347_driver = {
	.driver = {
		.name = "ds1347",
		.owner = THIS_MODULE,
	},
	.probe = ds1347_probe,
};

module_spi_driver(ds1347_driver);

MODULE_DESCRIPTION("DS1347 SPI RTC DRIVER");
MODULE_AUTHOR("Raghavendra C Ganiga <ravi23ganiga@gmail.com>");
MODULE_LICENSE("GPL v2");