1/*
2 * rtc class driver for the Maxim MAX6900 chip
3 *
4 * Author: Dale Farnsworth <dale@farnsworth.org>
5 *
6 * based on previously existing rtc class drivers
7 *
8 * 2007 (c) MontaVista, Software, Inc.  This file is licensed under
9 * the terms of the GNU General Public License version 2.  This program
10 * is licensed "as is" without any warranty of any kind, whether express
11 * or implied.
12 */
13
14#include <linux/module.h>
15#include <linux/i2c.h>
16#include <linux/bcd.h>
17#include <linux/rtc.h>
18#include <linux/delay.h>
19
20/*
21 * register indices
22 */
23#define MAX6900_REG_SC			0	/* seconds      00-59 */
24#define MAX6900_REG_MN			1	/* minutes      00-59 */
25#define MAX6900_REG_HR			2	/* hours        00-23 */
26#define MAX6900_REG_DT			3	/* day of month 00-31 */
27#define MAX6900_REG_MO			4	/* month        01-12 */
28#define MAX6900_REG_DW			5	/* day of week   1-7  */
29#define MAX6900_REG_YR			6	/* year         00-99 */
30#define MAX6900_REG_CT			7	/* control */
31						/* register 8 is undocumented */
32#define MAX6900_REG_CENTURY		9	/* century */
33#define MAX6900_REG_LEN			10
34
35#define MAX6900_BURST_LEN		8	/* can burst r/w first 8 regs */
36
37#define MAX6900_REG_CT_WP		(1 << 7)	/* Write Protect */
38
39/*
40 * register read/write commands
41 */
42#define MAX6900_REG_CONTROL_WRITE	0x8e
43#define MAX6900_REG_CENTURY_WRITE	0x92
44#define MAX6900_REG_CENTURY_READ	0x93
45#define MAX6900_REG_RESERVED_READ	0x96
46#define MAX6900_REG_BURST_WRITE		0xbe
47#define MAX6900_REG_BURST_READ		0xbf
48
49#define MAX6900_IDLE_TIME_AFTER_WRITE	3	/* specification says 2.5 mS */
50
51static struct i2c_driver max6900_driver;
52
53static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
54{
55	u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
56	u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
57	struct i2c_msg msgs[4] = {
58		{
59		 .addr = client->addr,
60		 .flags = 0,	/* write */
61		 .len = sizeof(reg_burst_read),
62		 .buf = reg_burst_read}
63		,
64		{
65		 .addr = client->addr,
66		 .flags = I2C_M_RD,
67		 .len = MAX6900_BURST_LEN,
68		 .buf = buf}
69		,
70		{
71		 .addr = client->addr,
72		 .flags = 0,	/* write */
73		 .len = sizeof(reg_century_read),
74		 .buf = reg_century_read}
75		,
76		{
77		 .addr = client->addr,
78		 .flags = I2C_M_RD,
79		 .len = sizeof(buf[MAX6900_REG_CENTURY]),
80		 .buf = &buf[MAX6900_REG_CENTURY]
81		 }
82	};
83	int rc;
84
85	rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
86	if (rc != ARRAY_SIZE(msgs)) {
87		dev_err(&client->dev, "%s: register read failed\n", __func__);
88		return -EIO;
89	}
90	return 0;
91}
92
93static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
94{
95	u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
96	struct i2c_msg century_msgs[1] = {
97		{
98		 .addr = client->addr,
99		 .flags = 0,	/* write */
100		 .len = sizeof(i2c_century_buf),
101		 .buf = i2c_century_buf}
102	};
103	u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
104	struct i2c_msg burst_msgs[1] = {
105		{
106		 .addr = client->addr,
107		 .flags = 0,	/* write */
108		 .len = sizeof(i2c_burst_buf),
109		 .buf = i2c_burst_buf}
110	};
111	int rc;
112
113	/*
114	 * We have to make separate calls to i2c_transfer because of
115	 * the need to delay after each write to the chip.  Also,
116	 * we write the century byte first, since we set the write-protect
117	 * bit as part of the burst write.
118	 */
119	i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];
120
121	rc = i2c_transfer(client->adapter, century_msgs,
122			  ARRAY_SIZE(century_msgs));
123	if (rc != ARRAY_SIZE(century_msgs))
124		goto write_failed;
125
126	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
127
128	memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);
129
130	rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
131	if (rc != ARRAY_SIZE(burst_msgs))
132		goto write_failed;
133	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
134
135	return 0;
136
137 write_failed:
138	dev_err(&client->dev, "%s: register write failed\n", __func__);
139	return -EIO;
140}
141
142static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
143{
144	struct i2c_client *client = to_i2c_client(dev);
145	int rc;
146	u8 regs[MAX6900_REG_LEN];
147
148	rc = max6900_i2c_read_regs(client, regs);
149	if (rc < 0)
150		return rc;
151
152	tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
153	tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
154	tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
155	tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
156	tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
157	tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
158		      bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
159	tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);
160
161	return 0;
162}
163
164static int max6900_i2c_clear_write_protect(struct i2c_client *client)
165{
166	return i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
167}
168
169static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
170{
171	struct i2c_client *client = to_i2c_client(dev);
172	u8 regs[MAX6900_REG_LEN];
173	int rc;
174
175	rc = max6900_i2c_clear_write_protect(client);
176	if (rc < 0)
177		return rc;
178
179	regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
180	regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
181	regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
182	regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
183	regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
184	regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
185	regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
186	regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
187	/* set write protect */
188	regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;
189
190	rc = max6900_i2c_write_regs(client, regs);
191	if (rc < 0)
192		return rc;
193
194	return 0;
195}
196
197static const struct rtc_class_ops max6900_rtc_ops = {
198	.read_time = max6900_rtc_read_time,
199	.set_time = max6900_rtc_set_time,
200};
201
202static int
203max6900_probe(struct i2c_client *client, const struct i2c_device_id *id)
204{
205	struct rtc_device *rtc;
206
207	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
208		return -ENODEV;
209
210	rtc = devm_rtc_device_register(&client->dev, max6900_driver.driver.name,
211					&max6900_rtc_ops, THIS_MODULE);
212	if (IS_ERR(rtc))
213		return PTR_ERR(rtc);
214
215	i2c_set_clientdata(client, rtc);
216
217	return 0;
218}
219
220static const struct i2c_device_id max6900_id[] = {
221	{ "max6900", 0 },
222	{ }
223};
224MODULE_DEVICE_TABLE(i2c, max6900_id);
225
226static struct i2c_driver max6900_driver = {
227	.driver = {
228		   .name = "rtc-max6900",
229		   },
230	.probe = max6900_probe,
231	.id_table = max6900_id,
232};
233
234module_i2c_driver(max6900_driver);
235
236MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
237MODULE_AUTHOR("Dale Farnsworth <dale@farnsworth.org>");
238MODULE_LICENSE("GPL");
239