Loading...
Note: File does not exist in v3.1.
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * ee1004 - driver for DDR4 SPD EEPROMs
4 *
5 * Copyright (C) 2017-2019 Jean Delvare
6 *
7 * Based on the at24 driver:
8 * Copyright (C) 2005-2007 David Brownell
9 * Copyright (C) 2008 Wolfram Sang, Pengutronix
10 */
11
12#include <linux/i2c.h>
13#include <linux/init.h>
14#include <linux/kernel.h>
15#include <linux/mod_devicetable.h>
16#include <linux/module.h>
17#include <linux/mutex.h>
18
19/*
20 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
21 * specification. These are 512-byte EEPROMs using a single I2C address
22 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
23 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
24 *
25 * Therefore we need to request these 2 additional addresses, and serialize
26 * access to all such EEPROMs with a single mutex.
27 *
28 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
29 * We use SMBus access even if I2C is available, these EEPROMs are small
30 * enough, and reading from them infrequent enough, that we favor simplicity
31 * over performance.
32 */
33
34#define EE1004_ADDR_SET_PAGE 0x36
35#define EE1004_EEPROM_SIZE 512
36#define EE1004_PAGE_SIZE 256
37#define EE1004_PAGE_SHIFT 8
38
39/*
40 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
41 * from page selection to end of read.
42 */
43static DEFINE_MUTEX(ee1004_bus_lock);
44static struct i2c_client *ee1004_set_page[2];
45static unsigned int ee1004_dev_count;
46static int ee1004_current_page;
47
48static const struct i2c_device_id ee1004_ids[] = {
49 { "ee1004", 0 },
50 { }
51};
52MODULE_DEVICE_TABLE(i2c, ee1004_ids);
53
54/*-------------------------------------------------------------------------*/
55
56static int ee1004_get_current_page(void)
57{
58 int err;
59
60 err = i2c_smbus_read_byte(ee1004_set_page[0]);
61 if (err == -ENXIO) {
62 /* Nack means page 1 is selected */
63 return 1;
64 }
65 if (err < 0) {
66 /* Anything else is a real error, bail out */
67 return err;
68 }
69
70 /* Ack means page 0 is selected, returned value meaningless */
71 return 0;
72}
73
74static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
75 unsigned int offset, size_t count)
76{
77 int status;
78
79 if (count > I2C_SMBUS_BLOCK_MAX)
80 count = I2C_SMBUS_BLOCK_MAX;
81 /* Can't cross page boundaries */
82 if (unlikely(offset + count > EE1004_PAGE_SIZE))
83 count = EE1004_PAGE_SIZE - offset;
84
85 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
86 count, buf);
87 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
88
89 return status;
90}
91
92static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
93 struct bin_attribute *bin_attr,
94 char *buf, loff_t off, size_t count)
95{
96 struct device *dev = kobj_to_dev(kobj);
97 struct i2c_client *client = to_i2c_client(dev);
98 size_t requested = count;
99 int page;
100
101 if (unlikely(!count))
102 return count;
103
104 page = off >> EE1004_PAGE_SHIFT;
105 if (unlikely(page > 1))
106 return 0;
107 off &= (1 << EE1004_PAGE_SHIFT) - 1;
108
109 /*
110 * Read data from chip, protecting against concurrent access to
111 * other EE1004 SPD EEPROMs on the same adapter.
112 */
113 mutex_lock(&ee1004_bus_lock);
114
115 while (count) {
116 int status;
117
118 /* Select page */
119 if (page != ee1004_current_page) {
120 /* Data is ignored */
121 status = i2c_smbus_write_byte(ee1004_set_page[page],
122 0x00);
123 if (status == -ENXIO) {
124 /*
125 * Don't give up just yet. Some memory
126 * modules will select the page but not
127 * ack the command. Check which page is
128 * selected now.
129 */
130 if (ee1004_get_current_page() == page)
131 status = 0;
132 }
133 if (status < 0) {
134 dev_err(dev, "Failed to select page %d (%d)\n",
135 page, status);
136 mutex_unlock(&ee1004_bus_lock);
137 return status;
138 }
139 dev_dbg(dev, "Selected page %d\n", page);
140 ee1004_current_page = page;
141 }
142
143 status = ee1004_eeprom_read(client, buf, off, count);
144 if (status < 0) {
145 mutex_unlock(&ee1004_bus_lock);
146 return status;
147 }
148 buf += status;
149 off += status;
150 count -= status;
151
152 if (off == EE1004_PAGE_SIZE) {
153 page++;
154 off = 0;
155 }
156 }
157
158 mutex_unlock(&ee1004_bus_lock);
159
160 return requested;
161}
162
163static const struct bin_attribute eeprom_attr = {
164 .attr = {
165 .name = "eeprom",
166 .mode = 0444,
167 },
168 .size = EE1004_EEPROM_SIZE,
169 .read = ee1004_read,
170};
171
172static int ee1004_probe(struct i2c_client *client,
173 const struct i2c_device_id *id)
174{
175 int err, cnr = 0;
176 const char *slow = NULL;
177
178 /* Make sure we can operate on this adapter */
179 if (!i2c_check_functionality(client->adapter,
180 I2C_FUNC_SMBUS_READ_BYTE |
181 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
182 if (i2c_check_functionality(client->adapter,
183 I2C_FUNC_SMBUS_READ_BYTE |
184 I2C_FUNC_SMBUS_READ_WORD_DATA))
185 slow = "word";
186 else if (i2c_check_functionality(client->adapter,
187 I2C_FUNC_SMBUS_READ_BYTE |
188 I2C_FUNC_SMBUS_READ_BYTE_DATA))
189 slow = "byte";
190 else
191 return -EPFNOSUPPORT;
192 }
193
194 /* Use 2 dummy devices for page select command */
195 mutex_lock(&ee1004_bus_lock);
196 if (++ee1004_dev_count == 1) {
197 for (cnr = 0; cnr < 2; cnr++) {
198 ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
199 EE1004_ADDR_SET_PAGE + cnr);
200 if (IS_ERR(ee1004_set_page[cnr])) {
201 dev_err(&client->dev,
202 "address 0x%02x unavailable\n",
203 EE1004_ADDR_SET_PAGE + cnr);
204 err = PTR_ERR(ee1004_set_page[cnr]);
205 goto err_clients;
206 }
207 }
208 } else if (i2c_adapter_id(client->adapter) !=
209 i2c_adapter_id(ee1004_set_page[0]->adapter)) {
210 dev_err(&client->dev,
211 "Driver only supports devices on a single I2C bus\n");
212 err = -EOPNOTSUPP;
213 goto err_clients;
214 }
215
216 /* Remember current page to avoid unneeded page select */
217 err = ee1004_get_current_page();
218 if (err < 0)
219 goto err_clients;
220 ee1004_current_page = err;
221 dev_dbg(&client->dev, "Currently selected page: %d\n",
222 ee1004_current_page);
223 mutex_unlock(&ee1004_bus_lock);
224
225 /* Create the sysfs eeprom file */
226 err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
227 if (err)
228 goto err_clients_lock;
229
230 dev_info(&client->dev,
231 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
232 EE1004_EEPROM_SIZE);
233 if (slow)
234 dev_notice(&client->dev,
235 "Falling back to %s reads, performance will suffer\n",
236 slow);
237
238 return 0;
239
240 err_clients_lock:
241 mutex_lock(&ee1004_bus_lock);
242 err_clients:
243 if (--ee1004_dev_count == 0) {
244 for (cnr--; cnr >= 0; cnr--) {
245 i2c_unregister_device(ee1004_set_page[cnr]);
246 ee1004_set_page[cnr] = NULL;
247 }
248 }
249 mutex_unlock(&ee1004_bus_lock);
250
251 return err;
252}
253
254static int ee1004_remove(struct i2c_client *client)
255{
256 int i;
257
258 sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
259
260 /* Remove page select clients if this is the last device */
261 mutex_lock(&ee1004_bus_lock);
262 if (--ee1004_dev_count == 0) {
263 for (i = 0; i < 2; i++) {
264 i2c_unregister_device(ee1004_set_page[i]);
265 ee1004_set_page[i] = NULL;
266 }
267 }
268 mutex_unlock(&ee1004_bus_lock);
269
270 return 0;
271}
272
273/*-------------------------------------------------------------------------*/
274
275static struct i2c_driver ee1004_driver = {
276 .driver = {
277 .name = "ee1004",
278 },
279 .probe = ee1004_probe,
280 .remove = ee1004_remove,
281 .id_table = ee1004_ids,
282};
283
284static int __init ee1004_init(void)
285{
286 return i2c_add_driver(&ee1004_driver);
287}
288module_init(ee1004_init);
289
290static void __exit ee1004_exit(void)
291{
292 i2c_del_driver(&ee1004_driver);
293}
294module_exit(ee1004_exit);
295
296MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
297MODULE_AUTHOR("Jean Delvare");
298MODULE_LICENSE("GPL");