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 */
45struct 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
54static 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	}
102exit_up:
103	mutex_unlock(&data->update_lock);
104}
105
106static 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
124static 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
133static 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
168exit_remove_fake:
169	i2c_unregister_device(data->fake_client);
170exit_kfree:
171	kfree(data);
172	return err;
173}
174
175static 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
185static const struct i2c_device_id max6875_id[] = {
186	{ "max6875", 0 },
187	{ }
188};
189MODULE_DEVICE_TABLE(i2c, max6875_id);
190
191static struct i2c_driver max6875_driver = {
192	.driver = {
193		.name	= "max6875",
194	},
195	.probe		= max6875_probe,
196	.remove		= max6875_remove,
197	.id_table	= max6875_id,
198};
199
200module_i2c_driver(max6875_driver);
201
202MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
203MODULE_DESCRIPTION("MAX6875 driver");
204MODULE_LICENSE("GPL");
205