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 
max6916_read_reg(struct device * dev,unsigned char address,unsigned char * data)35 static 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 
max6916_write_reg(struct device * dev,unsigned char address,unsigned char data)45 static 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 
max6916_read_time(struct device * dev,struct rtc_time * dt)57 static 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 
max6916_set_time(struct device * dev,struct rtc_time * dt)81 static 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 
106 static const struct rtc_class_ops max6916_rtc_ops = {
107 	.read_time = max6916_read_time,
108 	.set_time = max6916_set_time,
109 };
110 
max6916_probe(struct spi_device * spi)111 static 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 
154 static struct spi_driver max6916_driver = {
155 	.driver = {
156 		.name = "max6916",
157 	},
158 	.probe = max6916_probe,
159 };
160 module_spi_driver(max6916_driver);
161 
162 MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
163 MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
164 MODULE_LICENSE("GPL v2");
165