1/* rtc-max6916.c
  2 *
  3 * Driver for MAXIM  max6916 Low Current, SPI Compatible
  4 * Real Time Clock
  5 *
  6 * Author : Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
  7 *
  8 * This program is free software; you can redistribute it and/or modify
  9 * it under the terms of the GNU General Public License version 2 as
 10 * published by the Free Software Foundation.
 11 *
 12 */
 13
 14#include <linux/init.h>
 15#include <linux/module.h>
 16#include <linux/device.h>
 17#include <linux/platform_device.h>
 18#include <linux/rtc.h>
 19#include <linux/spi/spi.h>
 20#include <linux/bcd.h>
 21
 22/* Registers in max6916 rtc */
 23
 24#define MAX6916_SECONDS_REG	0x01
 25#define MAX6916_MINUTES_REG	0x02
 26#define MAX6916_HOURS_REG	0x03
 27#define MAX6916_DATE_REG	0x04
 28#define MAX6916_MONTH_REG	0x05
 29#define MAX6916_DAY_REG	0x06
 30#define MAX6916_YEAR_REG	0x07
 31#define MAX6916_CONTROL_REG	0x08
 32#define MAX6916_STATUS_REG	0x0C
 33#define MAX6916_CLOCK_BURST	0x3F
 34
 35static int max6916_read_reg(struct device *dev, unsigned char address,
 36			    unsigned char *data)
 37{
 38	struct spi_device *spi = to_spi_device(dev);
 39
 40	*data = address | 0x80;
 41
 42	return spi_write_then_read(spi, data, 1, data, 1);
 43}
 44
 45static int max6916_write_reg(struct device *dev, unsigned char address,
 46			     unsigned char data)
 47{
 48	struct spi_device *spi = to_spi_device(dev);
 49	unsigned char buf[2];
 50
 51	buf[0] = address & 0x7F;
 52	buf[1] = data;
 53
 54	return spi_write_then_read(spi, buf, 2, NULL, 0);
 55}
 56
 57static int max6916_read_time(struct device *dev, struct rtc_time *dt)
 58{
 59	struct spi_device *spi = to_spi_device(dev);
 60	int err;
 61	unsigned char buf[8];
 62
 63	buf[0] = MAX6916_CLOCK_BURST | 0x80;
 64
 65	err = spi_write_then_read(spi, buf, 1, buf, 8);
 66
 67	if (err)
 68		return err;
 69
 70	dt->tm_sec = bcd2bin(buf[0]);
 71	dt->tm_min = bcd2bin(buf[1]);
 72	dt->tm_hour = bcd2bin(buf[2] & 0x3F);
 73	dt->tm_mday = bcd2bin(buf[3]);
 74	dt->tm_mon = bcd2bin(buf[4]) - 1;
 75	dt->tm_wday = bcd2bin(buf[5]) - 1;
 76	dt->tm_year = bcd2bin(buf[6]) + 100;
 77
 78	return 0;
 79}
 80
 81static int max6916_set_time(struct device *dev, struct rtc_time *dt)
 82{
 83	struct spi_device *spi = to_spi_device(dev);
 84	unsigned char buf[9];
 85
 86	if (dt->tm_year < 100 || dt->tm_year > 199) {
 87		dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n",
 88			dt->tm_year + 1900);
 89	return -EINVAL;
 90	}
 91
 92	buf[0] = MAX6916_CLOCK_BURST & 0x7F;
 93	buf[1] = bin2bcd(dt->tm_sec);
 94	buf[2] = bin2bcd(dt->tm_min);
 95	buf[3] = (bin2bcd(dt->tm_hour) & 0X3F);
 96	buf[4] = bin2bcd(dt->tm_mday);
 97	buf[5] = bin2bcd(dt->tm_mon + 1);
 98	buf[6] = bin2bcd(dt->tm_wday + 1);
 99	buf[7] = bin2bcd(dt->tm_year % 100);
100	buf[8] = bin2bcd(0x00);
101
102	/* write the rtc settings */
103	return spi_write_then_read(spi, buf, 9, NULL, 0);
104}
105
106static const struct rtc_class_ops max6916_rtc_ops = {
107	.read_time = max6916_read_time,
108	.set_time = max6916_set_time,
109};
110
111static int max6916_probe(struct spi_device *spi)
112{
113	struct rtc_device *rtc;
114	unsigned char data;
115	int res;
116
117	/* spi setup with max6916 in mode 3 and bits per word as 8 */
118	spi->mode = SPI_MODE_3;
119	spi->bits_per_word = 8;
120	spi_setup(spi);
121
122	/* RTC Settings */
123	res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data);
124	if (res)
125		return res;
126
127	/* Disable the write protect of rtc */
128	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
129	data = data & ~(1 << 7);
130	max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data);
131
132	/*Enable oscillator,disable oscillator stop flag, glitch filter*/
133	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
134	data = data & 0x1B;
135	max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data);
136
137	/* display the settings */
138	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
139	dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data);
140
141	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
142	dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data);
143
144	rtc = devm_rtc_device_register(&spi->dev, "max6916",
145				       &max6916_rtc_ops, THIS_MODULE);
146	if (IS_ERR(rtc))
147		return PTR_ERR(rtc);
148
149	spi_set_drvdata(spi, rtc);
150
151	return 0;
152}
153
154static struct spi_driver max6916_driver = {
155	.driver = {
156		.name = "max6916",
157	},
158	.probe = max6916_probe,
159};
160module_spi_driver(max6916_driver);
161
162MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
163MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
164MODULE_LICENSE("GPL v2");