1 // SPDX-License-Identifier: GPL-2.0-only
2 /* drivers/rtc/rtc-max6902.c
4 * Copyright (C) 2006 8D Technologies inc.
5 * Copyright (C) 2004 Compulab Ltd.
7 * Driver for MAX6902 spi RTC
10 #include <linux/module.h>
11 #include <linux/kernel.h>
12 #include <linux/platform_device.h>
13 #include <linux/init.h>
14 #include <linux/rtc.h>
15 #include <linux/spi/spi.h>
16 #include <linux/bcd.h>
18 #define MAX6902_REG_SECONDS 0x01
19 #define MAX6902_REG_MINUTES 0x03
20 #define MAX6902_REG_HOURS 0x05
21 #define MAX6902_REG_DATE 0x07
22 #define MAX6902_REG_MONTH 0x09
23 #define MAX6902_REG_DAY 0x0B
24 #define MAX6902_REG_YEAR 0x0D
25 #define MAX6902_REG_CONTROL 0x0F
26 #define MAX6902_REG_CENTURY 0x13
28 static int max6902_set_reg(struct device *dev, unsigned char address,
31 struct spi_device *spi = to_spi_device(dev);
34 /* MSB must be '0' to write */
35 buf[0] = address & 0x7f;
38 return spi_write_then_read(spi, buf, 2, NULL, 0);
41 static int max6902_get_reg(struct device *dev, unsigned char address,
44 struct spi_device *spi = to_spi_device(dev);
46 /* Set MSB to indicate read */
47 *data = address | 0x80;
49 return spi_write_then_read(spi, data, 1, data, 1);
52 static int max6902_read_time(struct device *dev, struct rtc_time *dt)
55 struct spi_device *spi = to_spi_device(dev);
58 buf[0] = 0xbf; /* Burst read */
60 err = spi_write_then_read(spi, buf, 1, buf, 8);
64 /* The chip sends data in this order:
65 * Seconds, Minutes, Hours, Date, Month, Day, Year */
66 dt->tm_sec = bcd2bin(buf[0]);
67 dt->tm_min = bcd2bin(buf[1]);
68 dt->tm_hour = bcd2bin(buf[2]);
69 dt->tm_mday = bcd2bin(buf[3]);
70 dt->tm_mon = bcd2bin(buf[4]) - 1;
71 dt->tm_wday = bcd2bin(buf[5]);
72 dt->tm_year = bcd2bin(buf[6]);
75 err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]);
79 century = bcd2bin(buf[0]) * 100;
81 dt->tm_year += century;
87 static int max6902_set_time(struct device *dev, struct rtc_time *dt)
89 dt->tm_year = dt->tm_year + 1900;
91 /* Remove write protection */
92 max6902_set_reg(dev, MAX6902_REG_CONTROL, 0);
94 max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec));
95 max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min));
96 max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour));
98 max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday));
99 max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1));
100 max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday));
101 max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100));
102 max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100));
104 /* Compulab used a delay here. However, the datasheet
105 * does not mention a delay being required anywhere... */
109 max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80);
114 static const struct rtc_class_ops max6902_rtc_ops = {
115 .read_time = max6902_read_time,
116 .set_time = max6902_set_time,
119 static int max6902_probe(struct spi_device *spi)
121 struct rtc_device *rtc;
125 spi->mode = SPI_MODE_3;
126 spi->bits_per_word = 8;
129 res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp);
133 rtc = devm_rtc_device_register(&spi->dev, "max6902",
134 &max6902_rtc_ops, THIS_MODULE);
138 spi_set_drvdata(spi, rtc);
142 static struct spi_driver max6902_driver = {
144 .name = "rtc-max6902",
146 .probe = max6902_probe,
149 module_spi_driver(max6902_driver);
151 MODULE_DESCRIPTION("max6902 spi RTC driver");
152 MODULE_AUTHOR("Raphael Assenat");
153 MODULE_LICENSE("GPL");
154 MODULE_ALIAS("spi:rtc-max6902");