xref: /openbmc/linux/drivers/rtc/rtc-mcp795.c (revision f3539c12)
1 /*
2  * SPI Driver for Microchip MCP795 RTC
3  *
4  * Copyright (C) Josef Gajdusek <atx@atx.name>
5  *
6  * based on other Linux RTC drivers
7  *
8  * Device datasheet:
9  * http://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
10  *
11  * This program is free software; you can redistribute it and/or modify
12  * it under the terms of the GNU General Public License version 2 as
13  * published by the Free Software Foundation.
14  *
15  * */
16 
17 #include <linux/module.h>
18 #include <linux/kernel.h>
19 #include <linux/device.h>
20 #include <linux/printk.h>
21 #include <linux/spi/spi.h>
22 #include <linux/rtc.h>
23 #include <linux/of.h>
24 
25 /* MCP795 Instructions, see datasheet table 3-1 */
26 #define MCP795_EEREAD	0x03
27 #define MCP795_EEWRITE	0x02
28 #define MCP795_EEWRDI	0x04
29 #define MCP795_EEWREN	0x06
30 #define MCP795_SRREAD	0x05
31 #define MCP795_SRWRITE	0x01
32 #define MCP795_READ		0x13
33 #define MCP795_WRITE	0x12
34 #define MCP795_UNLOCK	0x14
35 #define MCP795_IDWRITE	0x32
36 #define MCP795_IDREAD	0x33
37 #define MCP795_CLRWDT	0x44
38 #define MCP795_CLRRAM	0x54
39 
40 #define MCP795_ST_BIT	0x80
41 #define MCP795_24_BIT	0x40
42 
43 static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
44 {
45 	struct spi_device *spi = to_spi_device(dev);
46 	int ret;
47 	u8 tx[2];
48 
49 	tx[0] = MCP795_READ;
50 	tx[1] = addr;
51 	ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
52 
53 	if (ret)
54 		dev_err(dev, "Failed reading %d bytes from address %x.\n",
55 					count, addr);
56 
57 	return ret;
58 }
59 
60 static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
61 {
62 	struct spi_device *spi = to_spi_device(dev);
63 	int ret;
64 	u8 tx[2 + count];
65 
66 	tx[0] = MCP795_WRITE;
67 	tx[1] = addr;
68 	memcpy(&tx[2], data, count);
69 
70 	ret = spi_write(spi, tx, 2 + count);
71 
72 	if (ret)
73 		dev_err(dev, "Failed to write %d bytes to address %x.\n",
74 					count, addr);
75 
76 	return ret;
77 }
78 
79 static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
80 {
81 	int ret;
82 	u8 tmp;
83 
84 	ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
85 	if (ret)
86 		return ret;
87 
88 	if ((tmp & mask) != state) {
89 		tmp = (tmp & ~mask) | state;
90 		ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
91 	}
92 
93 	return ret;
94 }
95 
96 static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
97 {
98 	int ret;
99 	u8 data[7];
100 
101 	/* Read first, so we can leave config bits untouched */
102 	ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
103 
104 	if (ret)
105 		return ret;
106 
107 	data[0] = (data[0] & 0x80) | ((tim->tm_sec / 10) << 4) | (tim->tm_sec % 10);
108 	data[1] = (data[1] & 0x80) | ((tim->tm_min / 10) << 4) | (tim->tm_min % 10);
109 	data[2] = ((tim->tm_hour / 10) << 4) | (tim->tm_hour % 10);
110 	data[4] = ((tim->tm_mday / 10) << 4) | ((tim->tm_mday) % 10);
111 	data[5] = (data[5] & 0x10) | (tim->tm_mon / 10) | (tim->tm_mon % 10);
112 
113 	if (tim->tm_year > 100)
114 		tim->tm_year -= 100;
115 
116 	data[6] = ((tim->tm_year / 10) << 4) | (tim->tm_year % 10);
117 
118 	ret = mcp795_rtcc_write(dev, 0x01, data, sizeof(data));
119 
120 	if (ret)
121 		return ret;
122 
123 	dev_dbg(dev, "Set mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
124 			tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
125 			tim->tm_hour, tim->tm_min, tim->tm_sec);
126 
127 	return 0;
128 }
129 
130 static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
131 {
132 	int ret;
133 	u8 data[7];
134 
135 	ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
136 
137 	if (ret)
138 		return ret;
139 
140 	tim->tm_sec		= ((data[0] & 0x70) >> 4) * 10 + (data[0] & 0x0f);
141 	tim->tm_min		= ((data[1] & 0x70) >> 4) * 10 + (data[1] & 0x0f);
142 	tim->tm_hour	= ((data[2] & 0x30) >> 4) * 10 + (data[2] & 0x0f);
143 	tim->tm_mday	= ((data[4] & 0x30) >> 4) * 10 + (data[4] & 0x0f);
144 	tim->tm_mon		= ((data[5] & 0x10) >> 4) * 10 + (data[5] & 0x0f);
145 	tim->tm_year	= ((data[6] & 0xf0) >> 4) * 10 + (data[6] & 0x0f) + 100; /* Assume we are in 20xx */
146 
147 	dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
148 				tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
149 				tim->tm_hour, tim->tm_min, tim->tm_sec);
150 
151 	return rtc_valid_tm(tim);
152 }
153 
154 static struct rtc_class_ops mcp795_rtc_ops = {
155 		.read_time = mcp795_read_time,
156 		.set_time = mcp795_set_time
157 };
158 
159 static int mcp795_probe(struct spi_device *spi)
160 {
161 	struct rtc_device *rtc;
162 	int ret;
163 
164 	spi->mode = SPI_MODE_0;
165 	spi->bits_per_word = 8;
166 	ret = spi_setup(spi);
167 	if (ret) {
168 		dev_err(&spi->dev, "Unable to setup SPI\n");
169 		return ret;
170 	}
171 
172 	/* Start the oscillator */
173 	mcp795_rtcc_set_bits(&spi->dev, 0x01, MCP795_ST_BIT, MCP795_ST_BIT);
174 	/* Clear the 12 hour mode flag*/
175 	mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
176 
177 	rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
178 								&mcp795_rtc_ops, THIS_MODULE);
179 	if (IS_ERR(rtc))
180 		return PTR_ERR(rtc);
181 
182 	spi_set_drvdata(spi, rtc);
183 
184 	return 0;
185 }
186 
187 #ifdef CONFIG_OF
188 static const struct of_device_id mcp795_of_match[] = {
189 	{ .compatible = "maxim,mcp795" },
190 	{ }
191 };
192 MODULE_DEVICE_TABLE(of, mcp795_of_match);
193 #endif
194 
195 static struct spi_driver mcp795_driver = {
196 		.driver = {
197 				.name = "rtc-mcp795",
198 				.of_match_table = of_match_ptr(mcp795_of_match),
199 		},
200 		.probe = mcp795_probe,
201 };
202 
203 module_spi_driver(mcp795_driver);
204 
205 MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
206 MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
207 MODULE_LICENSE("GPL");
208 MODULE_ALIAS("spi:mcp795");
209