1// SPDX-License-Identifier: GPL-2.0-only
  2/* rtc-max6916.c
  3 *
  4 * Driver for MAXIM  max6916 Low Current, SPI Compatible
  5 * Real Time Clock
  6 *
  7 * Author : Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
  8 */
  9
 10#include <linux/init.h>
 11#include <linux/module.h>
 12#include <linux/device.h>
 13#include <linux/platform_device.h>
 14#include <linux/rtc.h>
 15#include <linux/spi/spi.h>
 16#include <linux/bcd.h>
 17
 18/* Registers in max6916 rtc */
 19
 20#define MAX6916_SECONDS_REG	0x01
 21#define MAX6916_MINUTES_REG	0x02
 22#define MAX6916_HOURS_REG	0x03
 23#define MAX6916_DATE_REG	0x04
 24#define MAX6916_MONTH_REG	0x05
 25#define MAX6916_DAY_REG	0x06
 26#define MAX6916_YEAR_REG	0x07
 27#define MAX6916_CONTROL_REG	0x08
 28#define MAX6916_STATUS_REG	0x0C
 29#define MAX6916_CLOCK_BURST	0x3F
 30
 31static int max6916_read_reg(struct device *dev, unsigned char address,
 32			    unsigned char *data)
 33{
 34	struct spi_device *spi = to_spi_device(dev);
 35
 36	*data = address | 0x80;
 37
 38	return spi_write_then_read(spi, data, 1, data, 1);
 39}
 40
 41static int max6916_write_reg(struct device *dev, unsigned char address,
 42			     unsigned char data)
 43{
 44	struct spi_device *spi = to_spi_device(dev);
 45	unsigned char buf[2];
 46
 47	buf[0] = address & 0x7F;
 48	buf[1] = data;
 49
 50	return spi_write_then_read(spi, buf, 2, NULL, 0);
 51}
 52
 53static int max6916_read_time(struct device *dev, struct rtc_time *dt)
 54{
 55	struct spi_device *spi = to_spi_device(dev);
 56	int err;
 57	unsigned char buf[8];
 58
 59	buf[0] = MAX6916_CLOCK_BURST | 0x80;
 60
 61	err = spi_write_then_read(spi, buf, 1, buf, 8);
 62
 63	if (err)
 64		return err;
 65
 66	dt->tm_sec = bcd2bin(buf[0]);
 67	dt->tm_min = bcd2bin(buf[1]);
 68	dt->tm_hour = bcd2bin(buf[2] & 0x3F);
 69	dt->tm_mday = bcd2bin(buf[3]);
 70	dt->tm_mon = bcd2bin(buf[4]) - 1;
 71	dt->tm_wday = bcd2bin(buf[5]) - 1;
 72	dt->tm_year = bcd2bin(buf[6]) + 100;
 73
 74	return 0;
 75}
 76
 77static int max6916_set_time(struct device *dev, struct rtc_time *dt)
 78{
 79	struct spi_device *spi = to_spi_device(dev);
 80	unsigned char buf[9];
 81
 82	if (dt->tm_year < 100 || dt->tm_year > 199) {
 83		dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n",
 84			dt->tm_year + 1900);
 85		return -EINVAL;
 86	}
 87
 88	buf[0] = MAX6916_CLOCK_BURST & 0x7F;
 89	buf[1] = bin2bcd(dt->tm_sec);
 90	buf[2] = bin2bcd(dt->tm_min);
 91	buf[3] = (bin2bcd(dt->tm_hour) & 0X3F);
 92	buf[4] = bin2bcd(dt->tm_mday);
 93	buf[5] = bin2bcd(dt->tm_mon + 1);
 94	buf[6] = bin2bcd(dt->tm_wday + 1);
 95	buf[7] = bin2bcd(dt->tm_year % 100);
 96	buf[8] = bin2bcd(0x00);
 97
 98	/* write the rtc settings */
 99	return spi_write_then_read(spi, buf, 9, NULL, 0);
100}
101
102static const struct rtc_class_ops max6916_rtc_ops = {
103	.read_time = max6916_read_time,
104	.set_time = max6916_set_time,
105};
106
107static int max6916_probe(struct spi_device *spi)
108{
109	struct rtc_device *rtc;
110	unsigned char data;
111	int res;
112
113	/* spi setup with max6916 in mode 3 and bits per word as 8 */
114	spi->mode = SPI_MODE_3;
115	spi->bits_per_word = 8;
116	spi_setup(spi);
117
118	/* RTC Settings */
119	res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data);
120	if (res)
121		return res;
122
123	/* Disable the write protect of rtc */
124	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
125	data = data & ~(1 << 7);
126	max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data);
127
128	/*Enable oscillator,disable oscillator stop flag, glitch filter*/
129	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
130	data = data & 0x1B;
131	max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data);
132
133	/* display the settings */
134	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
135	dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data);
136
137	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
138	dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data);
139
140	rtc = devm_rtc_device_register(&spi->dev, "max6916",
141				       &max6916_rtc_ops, THIS_MODULE);
142	if (IS_ERR(rtc))
143		return PTR_ERR(rtc);
144
145	spi_set_drvdata(spi, rtc);
146
147	return 0;
148}
149
150static struct spi_driver max6916_driver = {
151	.driver = {
152		.name = "max6916",
153	},
154	.probe = max6916_probe,
155};
156module_spi_driver(max6916_driver);
157
158MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
159MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
160MODULE_LICENSE("GPL v2");