1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * max6875.c - driver for MAX6874/MAX6875
4  *
5  * Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>
6  *
7  * Based on eeprom.c
8  *
9  * The MAX6875 has a bank of registers and two banks of EEPROM.
10  * Address ranges are defined as follows:
11  *  * 0x0000 - 0x0046 = configuration registers
12  *  * 0x8000 - 0x8046 = configuration EEPROM
13  *  * 0x8100 - 0x82FF = user EEPROM
14  *
15  * This driver makes the user EEPROM available for read.
16  *
17  * The registers & config EEPROM should be accessed via i2c-dev.
18  *
19  * The MAX6875 ignores the lowest address bit, so each chip responds to
20  * two addresses - 0x50/0x51 and 0x52/0x53.
21  *
22  * Note that the MAX6875 uses i2c_smbus_write_byte_data() to set the read
23  * address, so this driver is destructive if loaded for the wrong EEPROM chip.
24  */
25 
26 #include <linux/kernel.h>
27 #include <linux/module.h>
28 #include <linux/slab.h>
29 #include <linux/i2c.h>
30 #include <linux/mutex.h>
31 
32 /* The MAX6875 can only read/write 16 bytes at a time */
33 #define SLICE_SIZE			16
34 #define SLICE_BITS			4
35 
36 /* USER EEPROM is at addresses 0x8100 - 0x82FF */
37 #define USER_EEPROM_BASE		0x8100
38 #define USER_EEPROM_SIZE		0x0200
39 #define USER_EEPROM_SLICES		32
40 
41 /* MAX6875 commands */
42 #define MAX6875_CMD_BLK_READ		0x84
43 
44 /* Each client has this additional data */
45 struct max6875_data {
46 	struct i2c_client	*fake_client;
47 	struct mutex		update_lock;
48 
49 	u32			valid;
50 	u8			data[USER_EEPROM_SIZE];
51 	unsigned long		last_updated[USER_EEPROM_SLICES];
52 };
53 
max6875_update_slice(struct i2c_client * client,int slice)54 static void max6875_update_slice(struct i2c_client *client, int slice)
55 {
56 	struct max6875_data *data = i2c_get_clientdata(client);
57 	int i, j, addr;
58 	u8 *buf;
59 
60 	if (slice >= USER_EEPROM_SLICES)
61 		return;
62 
63 	mutex_lock(&data->update_lock);
64 
65 	buf = &data->data[slice << SLICE_BITS];
66 
67 	if (!(data->valid & (1 << slice)) ||
68 	    time_after(jiffies, data->last_updated[slice])) {
69 
70 		dev_dbg(&client->dev, "Starting update of slice %u\n", slice);
71 
72 		data->valid &= ~(1 << slice);
73 
74 		addr = USER_EEPROM_BASE + (slice << SLICE_BITS);
75 
76 		/* select the eeprom address */
77 		if (i2c_smbus_write_byte_data(client, addr >> 8, addr & 0xFF)) {
78 			dev_err(&client->dev, "address set failed\n");
79 			goto exit_up;
80 		}
81 
82 		if (i2c_check_functionality(client->adapter,
83 					    I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
84 			if (i2c_smbus_read_i2c_block_data(client,
85 							  MAX6875_CMD_BLK_READ,
86 							  SLICE_SIZE,
87 							  buf) != SLICE_SIZE) {
88 				goto exit_up;
89 			}
90 		} else {
91 			for (i = 0; i < SLICE_SIZE; i++) {
92 				j = i2c_smbus_read_byte(client);
93 				if (j < 0) {
94 					goto exit_up;
95 				}
96 				buf[i] = j;
97 			}
98 		}
99 		data->last_updated[slice] = jiffies;
100 		data->valid |= (1 << slice);
101 	}
102 exit_up:
103 	mutex_unlock(&data->update_lock);
104 }
105 
max6875_read(struct file * filp,struct kobject * kobj,struct bin_attribute * bin_attr,char * buf,loff_t off,size_t count)106 static ssize_t max6875_read(struct file *filp, struct kobject *kobj,
107 			    struct bin_attribute *bin_attr,
108 			    char *buf, loff_t off, size_t count)
109 {
110 	struct i2c_client *client = kobj_to_i2c_client(kobj);
111 	struct max6875_data *data = i2c_get_clientdata(client);
112 	int slice, max_slice;
113 
114 	/* refresh slices which contain requested bytes */
115 	max_slice = (off + count - 1) >> SLICE_BITS;
116 	for (slice = (off >> SLICE_BITS); slice <= max_slice; slice++)
117 		max6875_update_slice(client, slice);
118 
119 	memcpy(buf, &data->data[off], count);
120 
121 	return count;
122 }
123 
124 static const struct bin_attribute user_eeprom_attr = {
125 	.attr = {
126 		.name = "eeprom",
127 		.mode = S_IRUGO,
128 	},
129 	.size = USER_EEPROM_SIZE,
130 	.read = max6875_read,
131 };
132 
max6875_probe(struct i2c_client * client)133 static int max6875_probe(struct i2c_client *client)
134 {
135 	struct i2c_adapter *adapter = client->adapter;
136 	struct max6875_data *data;
137 	int err;
138 
139 	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA
140 				     | I2C_FUNC_SMBUS_READ_BYTE))
141 		return -ENODEV;
142 
143 	/* Only bind to even addresses */
144 	if (client->addr & 1)
145 		return -ENODEV;
146 
147 	data = kzalloc(sizeof(struct max6875_data), GFP_KERNEL);
148 	if (!data)
149 		return -ENOMEM;
150 
151 	/* A fake client is created on the odd address */
152 	data->fake_client = i2c_new_dummy_device(client->adapter, client->addr + 1);
153 	if (IS_ERR(data->fake_client)) {
154 		err = PTR_ERR(data->fake_client);
155 		goto exit_kfree;
156 	}
157 
158 	/* Init real i2c_client */
159 	i2c_set_clientdata(client, data);
160 	mutex_init(&data->update_lock);
161 
162 	err = sysfs_create_bin_file(&client->dev.kobj, &user_eeprom_attr);
163 	if (err)
164 		goto exit_remove_fake;
165 
166 	return 0;
167 
168 exit_remove_fake:
169 	i2c_unregister_device(data->fake_client);
170 exit_kfree:
171 	kfree(data);
172 	return err;
173 }
174 
max6875_remove(struct i2c_client * client)175 static void max6875_remove(struct i2c_client *client)
176 {
177 	struct max6875_data *data = i2c_get_clientdata(client);
178 
179 	i2c_unregister_device(data->fake_client);
180 
181 	sysfs_remove_bin_file(&client->dev.kobj, &user_eeprom_attr);
182 	kfree(data);
183 }
184 
185 static const struct i2c_device_id max6875_id[] = {
186 	{ "max6875", 0 },
187 	{ }
188 };
189 MODULE_DEVICE_TABLE(i2c, max6875_id);
190 
191 static struct i2c_driver max6875_driver = {
192 	.driver = {
193 		.name	= "max6875",
194 	},
195 	.probe_new	= max6875_probe,
196 	.remove		= max6875_remove,
197 	.id_table	= max6875_id,
198 };
199 
200 module_i2c_driver(max6875_driver);
201 
202 MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
203 MODULE_DESCRIPTION("MAX6875 driver");
204 MODULE_LICENSE("GPL");
205