1/*
2 *
3 * Driver for ST M41T93 SPI RTC
4 *
5 * (c) 2010 Nikolaus Voss, Weinmann Medical GmbH
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 */
11
12#include <linux/bcd.h>
13#include <linux/kernel.h>
14#include <linux/module.h>
15#include <linux/platform_device.h>
16#include <linux/rtc.h>
17#include <linux/spi/spi.h>
18
19#define M41T93_REG_SSEC			0
20#define M41T93_REG_ST_SEC		1
21#define M41T93_REG_MIN			2
22#define M41T93_REG_CENT_HOUR		3
23#define M41T93_REG_WDAY			4
24#define M41T93_REG_DAY			5
25#define M41T93_REG_MON			6
26#define M41T93_REG_YEAR			7
27
28
29#define M41T93_REG_ALM_HOUR_HT		0xc
30#define M41T93_REG_FLAGS		0xf
31
32#define M41T93_FLAG_ST			(1 << 7)
33#define M41T93_FLAG_OF			(1 << 2)
34#define M41T93_FLAG_BL			(1 << 4)
35#define M41T93_FLAG_HT			(1 << 6)
36
37static inline int m41t93_set_reg(struct spi_device *spi, u8 addr, u8 data)
38{
39	u8 buf[2];
40
41	/* MSB must be '1' to write */
42	buf[0] = addr | 0x80;
43	buf[1] = data;
44
45	return spi_write(spi, buf, sizeof(buf));
46}
47
48static int m41t93_set_time(struct device *dev, struct rtc_time *tm)
49{
50	struct spi_device *spi = to_spi_device(dev);
51	int tmp;
52	u8 buf[9] = {0x80};        /* write cmd + 8 data bytes */
53	u8 * const data = &buf[1]; /* ptr to first data byte */
54
55	dev_dbg(dev, "%s secs=%d, mins=%d, "
56		"hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
57		"write", tm->tm_sec, tm->tm_min,
58		tm->tm_hour, tm->tm_mday,
59		tm->tm_mon, tm->tm_year, tm->tm_wday);
60
61	if (tm->tm_year < 100) {
62		dev_warn(&spi->dev, "unsupported date (before 2000-01-01).\n");
63		return -EINVAL;
64	}
65
66	tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
67	if (tmp < 0)
68		return tmp;
69
70	if (tmp & M41T93_FLAG_OF) {
71		dev_warn(&spi->dev, "OF bit is set, resetting.\n");
72		m41t93_set_reg(spi, M41T93_REG_FLAGS, tmp & ~M41T93_FLAG_OF);
73
74		tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
75		if (tmp < 0) {
76			return tmp;
77		} else if (tmp & M41T93_FLAG_OF) {
78			/* OF cannot be immediately reset: oscillator has to be
79			 * restarted. */
80			u8 reset_osc = buf[M41T93_REG_ST_SEC] | M41T93_FLAG_ST;
81
82			dev_warn(&spi->dev,
83				 "OF bit is still set, kickstarting clock.\n");
84			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
85			reset_osc &= ~M41T93_FLAG_ST;
86			m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
87		}
88	}
89
90	data[M41T93_REG_SSEC]		= 0;
91	data[M41T93_REG_ST_SEC]		= bin2bcd(tm->tm_sec);
92	data[M41T93_REG_MIN]		= bin2bcd(tm->tm_min);
93	data[M41T93_REG_CENT_HOUR]	= bin2bcd(tm->tm_hour) |
94						((tm->tm_year/100-1) << 6);
95	data[M41T93_REG_DAY]		= bin2bcd(tm->tm_mday);
96	data[M41T93_REG_WDAY]		= bin2bcd(tm->tm_wday + 1);
97	data[M41T93_REG_MON]		= bin2bcd(tm->tm_mon + 1);
98	data[M41T93_REG_YEAR]		= bin2bcd(tm->tm_year % 100);
99
100	return spi_write(spi, buf, sizeof(buf));
101}
102
103
104static int m41t93_get_time(struct device *dev, struct rtc_time *tm)
105{
106	struct spi_device *spi = to_spi_device(dev);
107	const u8 start_addr = 0;
108	u8 buf[8];
109	int century_after_1900;
110	int tmp;
111	int ret = 0;
112
113	/* Check status of clock. Two states must be considered:
114	   1. halt bit (HT) is set: the clock is running but update of readout
115	      registers has been disabled due to power failure. This is normal
116	      case after poweron. Time is valid after resetting HT bit.
117	   2. oscillator fail bit (OF) is set: time is invalid.
118	*/
119	tmp = spi_w8r8(spi, M41T93_REG_ALM_HOUR_HT);
120	if (tmp < 0)
121		return tmp;
122
123	if (tmp & M41T93_FLAG_HT) {
124		dev_dbg(&spi->dev, "HT bit is set, reenable clock update.\n");
125		m41t93_set_reg(spi, M41T93_REG_ALM_HOUR_HT,
126			       tmp & ~M41T93_FLAG_HT);
127	}
128
129	tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
130	if (tmp < 0)
131		return tmp;
132
133	if (tmp & M41T93_FLAG_OF) {
134		ret = -EINVAL;
135		dev_warn(&spi->dev, "OF bit is set, write time to restart.\n");
136	}
137
138	if (tmp & M41T93_FLAG_BL)
139		dev_warn(&spi->dev, "BL bit is set, replace battery.\n");
140
141	/* read actual time/date */
142	tmp = spi_write_then_read(spi, &start_addr, 1, buf, sizeof(buf));
143	if (tmp < 0)
144		return tmp;
145
146	tm->tm_sec	= bcd2bin(buf[M41T93_REG_ST_SEC]);
147	tm->tm_min	= bcd2bin(buf[M41T93_REG_MIN]);
148	tm->tm_hour	= bcd2bin(buf[M41T93_REG_CENT_HOUR] & 0x3f);
149	tm->tm_mday	= bcd2bin(buf[M41T93_REG_DAY]);
150	tm->tm_mon	= bcd2bin(buf[M41T93_REG_MON]) - 1;
151	tm->tm_wday	= bcd2bin(buf[M41T93_REG_WDAY] & 0x0f) - 1;
152
153	century_after_1900 = (buf[M41T93_REG_CENT_HOUR] >> 6) + 1;
154	tm->tm_year = bcd2bin(buf[M41T93_REG_YEAR]) + century_after_1900 * 100;
155
156	dev_dbg(dev, "%s secs=%d, mins=%d, "
157		"hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
158		"read", tm->tm_sec, tm->tm_min,
159		tm->tm_hour, tm->tm_mday,
160		tm->tm_mon, tm->tm_year, tm->tm_wday);
161
162	return ret < 0 ? ret : rtc_valid_tm(tm);
163}
164
165
166static const struct rtc_class_ops m41t93_rtc_ops = {
167	.read_time	= m41t93_get_time,
168	.set_time	= m41t93_set_time,
169};
170
171static struct spi_driver m41t93_driver;
172
173static int m41t93_probe(struct spi_device *spi)
174{
175	struct rtc_device *rtc;
176	int res;
177
178	spi->bits_per_word = 8;
179	spi_setup(spi);
180
181	res = spi_w8r8(spi, M41T93_REG_WDAY);
182	if (res < 0 || (res & 0xf8) != 0) {
183		dev_err(&spi->dev, "not found 0x%x.\n", res);
184		return -ENODEV;
185	}
186
187	rtc = devm_rtc_device_register(&spi->dev, m41t93_driver.driver.name,
188					&m41t93_rtc_ops, THIS_MODULE);
189	if (IS_ERR(rtc))
190		return PTR_ERR(rtc);
191
192	spi_set_drvdata(spi, rtc);
193
194	return 0;
195}
196
197static struct spi_driver m41t93_driver = {
198	.driver = {
199		.name	= "rtc-m41t93",
200		.owner	= THIS_MODULE,
201	},
202	.probe	= m41t93_probe,
203};
204
205module_spi_driver(m41t93_driver);
206
207MODULE_AUTHOR("Nikolaus Voss <n.voss@weinmann.de>");
208MODULE_DESCRIPTION("Driver for ST M41T93 SPI RTC");
209MODULE_LICENSE("GPL");
210MODULE_ALIAS("spi:rtc-m41t93");
211