1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * rtc class driver for the Maxim MAX6900 chip
4 *
5 * Copyright (c) 2007 MontaVista, Software, Inc.
6 *
7 * Author: Dale Farnsworth <dale@farnsworth.org>
8 *
9 * based on previously existing rtc class drivers
10 */
11
12#include <linux/module.h>
13#include <linux/i2c.h>
14#include <linux/bcd.h>
15#include <linux/rtc.h>
16#include <linux/delay.h>
17
18/*
19 * register indices
20 */
21#define MAX6900_REG_SC			0	/* seconds      00-59 */
22#define MAX6900_REG_MN			1	/* minutes      00-59 */
23#define MAX6900_REG_HR			2	/* hours        00-23 */
24#define MAX6900_REG_DT			3	/* day of month 00-31 */
25#define MAX6900_REG_MO			4	/* month        01-12 */
26#define MAX6900_REG_DW			5	/* day of week   1-7  */
27#define MAX6900_REG_YR			6	/* year         00-99 */
28#define MAX6900_REG_CT			7	/* control */
29						/* register 8 is undocumented */
30#define MAX6900_REG_CENTURY		9	/* century */
31#define MAX6900_REG_LEN			10
32
33#define MAX6900_BURST_LEN		8	/* can burst r/w first 8 regs */
34
35#define MAX6900_REG_CT_WP		(1 << 7)	/* Write Protect */
36
37/*
38 * register read/write commands
39 */
40#define MAX6900_REG_CONTROL_WRITE	0x8e
41#define MAX6900_REG_CENTURY_WRITE	0x92
42#define MAX6900_REG_CENTURY_READ	0x93
43#define MAX6900_REG_RESERVED_READ	0x96
44#define MAX6900_REG_BURST_WRITE		0xbe
45#define MAX6900_REG_BURST_READ		0xbf
46
47#define MAX6900_IDLE_TIME_AFTER_WRITE	3	/* specification says 2.5 mS */
48
49static struct i2c_driver max6900_driver;
50
51static int max6900_i2c_read_regs(struct i2c_client *client, u8 *buf)
52{
53	u8 reg_burst_read[1] = { MAX6900_REG_BURST_READ };
54	u8 reg_century_read[1] = { MAX6900_REG_CENTURY_READ };
55	struct i2c_msg msgs[4] = {
56		{
57		 .addr = client->addr,
58		 .flags = 0,	/* write */
59		 .len = sizeof(reg_burst_read),
60		 .buf = reg_burst_read}
61		,
62		{
63		 .addr = client->addr,
64		 .flags = I2C_M_RD,
65		 .len = MAX6900_BURST_LEN,
66		 .buf = buf}
67		,
68		{
69		 .addr = client->addr,
70		 .flags = 0,	/* write */
71		 .len = sizeof(reg_century_read),
72		 .buf = reg_century_read}
73		,
74		{
75		 .addr = client->addr,
76		 .flags = I2C_M_RD,
77		 .len = sizeof(buf[MAX6900_REG_CENTURY]),
78		 .buf = &buf[MAX6900_REG_CENTURY]
79		 }
80	};
81	int rc;
82
83	rc = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs));
84	if (rc != ARRAY_SIZE(msgs)) {
85		dev_err(&client->dev, "%s: register read failed\n", __func__);
86		return -EIO;
87	}
88	return 0;
89}
90
91static int max6900_i2c_write_regs(struct i2c_client *client, u8 const *buf)
92{
93	u8 i2c_century_buf[1 + 1] = { MAX6900_REG_CENTURY_WRITE };
94	struct i2c_msg century_msgs[1] = {
95		{
96		 .addr = client->addr,
97		 .flags = 0,	/* write */
98		 .len = sizeof(i2c_century_buf),
99		 .buf = i2c_century_buf}
100	};
101	u8 i2c_burst_buf[MAX6900_BURST_LEN + 1] = { MAX6900_REG_BURST_WRITE };
102	struct i2c_msg burst_msgs[1] = {
103		{
104		 .addr = client->addr,
105		 .flags = 0,	/* write */
106		 .len = sizeof(i2c_burst_buf),
107		 .buf = i2c_burst_buf}
108	};
109	int rc;
110
111	/*
112	 * We have to make separate calls to i2c_transfer because of
113	 * the need to delay after each write to the chip.  Also,
114	 * we write the century byte first, since we set the write-protect
115	 * bit as part of the burst write.
116	 */
117	i2c_century_buf[1] = buf[MAX6900_REG_CENTURY];
118
119	rc = i2c_transfer(client->adapter, century_msgs,
120			  ARRAY_SIZE(century_msgs));
121	if (rc != ARRAY_SIZE(century_msgs))
122		goto write_failed;
123
124	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
125
126	memcpy(&i2c_burst_buf[1], buf, MAX6900_BURST_LEN);
127
128	rc = i2c_transfer(client->adapter, burst_msgs, ARRAY_SIZE(burst_msgs));
129	if (rc != ARRAY_SIZE(burst_msgs))
130		goto write_failed;
131	msleep(MAX6900_IDLE_TIME_AFTER_WRITE);
132
133	return 0;
134
135 write_failed:
136	dev_err(&client->dev, "%s: register write failed\n", __func__);
137	return -EIO;
138}
139
140static int max6900_rtc_read_time(struct device *dev, struct rtc_time *tm)
141{
142	struct i2c_client *client = to_i2c_client(dev);
143	int rc;
144	u8 regs[MAX6900_REG_LEN];
145
146	rc = max6900_i2c_read_regs(client, regs);
147	if (rc < 0)
148		return rc;
149
150	tm->tm_sec = bcd2bin(regs[MAX6900_REG_SC]);
151	tm->tm_min = bcd2bin(regs[MAX6900_REG_MN]);
152	tm->tm_hour = bcd2bin(regs[MAX6900_REG_HR] & 0x3f);
153	tm->tm_mday = bcd2bin(regs[MAX6900_REG_DT]);
154	tm->tm_mon = bcd2bin(regs[MAX6900_REG_MO]) - 1;
155	tm->tm_year = bcd2bin(regs[MAX6900_REG_YR]) +
156		      bcd2bin(regs[MAX6900_REG_CENTURY]) * 100 - 1900;
157	tm->tm_wday = bcd2bin(regs[MAX6900_REG_DW]);
158
159	return 0;
160}
161
162static int max6900_i2c_clear_write_protect(struct i2c_client *client)
163{
164	return i2c_smbus_write_byte_data(client, MAX6900_REG_CONTROL_WRITE, 0);
165}
166
167static int max6900_rtc_set_time(struct device *dev, struct rtc_time *tm)
168{
169	struct i2c_client *client = to_i2c_client(dev);
170	u8 regs[MAX6900_REG_LEN];
171	int rc;
172
173	rc = max6900_i2c_clear_write_protect(client);
174	if (rc < 0)
175		return rc;
176
177	regs[MAX6900_REG_SC] = bin2bcd(tm->tm_sec);
178	regs[MAX6900_REG_MN] = bin2bcd(tm->tm_min);
179	regs[MAX6900_REG_HR] = bin2bcd(tm->tm_hour);
180	regs[MAX6900_REG_DT] = bin2bcd(tm->tm_mday);
181	regs[MAX6900_REG_MO] = bin2bcd(tm->tm_mon + 1);
182	regs[MAX6900_REG_DW] = bin2bcd(tm->tm_wday);
183	regs[MAX6900_REG_YR] = bin2bcd(tm->tm_year % 100);
184	regs[MAX6900_REG_CENTURY] = bin2bcd((tm->tm_year + 1900) / 100);
185	/* set write protect */
186	regs[MAX6900_REG_CT] = MAX6900_REG_CT_WP;
187
188	rc = max6900_i2c_write_regs(client, regs);
189	if (rc < 0)
190		return rc;
191
192	return 0;
193}
194
195static const struct rtc_class_ops max6900_rtc_ops = {
196	.read_time = max6900_rtc_read_time,
197	.set_time = max6900_rtc_set_time,
198};
199
200static int max6900_probe(struct i2c_client *client)
201{
202	struct rtc_device *rtc;
203
204	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
205		return -ENODEV;
206
207	rtc = devm_rtc_device_register(&client->dev, max6900_driver.driver.name,
208					&max6900_rtc_ops, THIS_MODULE);
209	if (IS_ERR(rtc))
210		return PTR_ERR(rtc);
211
212	i2c_set_clientdata(client, rtc);
213
214	return 0;
215}
216
217static const struct i2c_device_id max6900_id[] = {
218	{ "max6900", 0 },
219	{ }
220};
221MODULE_DEVICE_TABLE(i2c, max6900_id);
222
223static struct i2c_driver max6900_driver = {
224	.driver = {
225		   .name = "rtc-max6900",
226		   },
227	.probe = max6900_probe,
228	.id_table = max6900_id,
229};
230
231module_i2c_driver(max6900_driver);
232
233MODULE_DESCRIPTION("Maxim MAX6900 RTC driver");
234MODULE_AUTHOR("Dale Farnsworth <dale@farnsworth.org>");
235MODULE_LICENSE("GPL");
236