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