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 */
43 static DEFINE_MUTEX(ee1004_bus_lock);
44 static struct i2c_client *ee1004_set_page[2];
45 static unsigned int ee1004_dev_count;
46 static int ee1004_current_page;
47
48 static const struct i2c_device_id ee1004_ids[] = {
49 { "ee1004", 0 },
50 { }
51 };
52 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
53
54 /*-------------------------------------------------------------------------*/
55
ee1004_get_current_page(void)56 static 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
ee1004_eeprom_read(struct i2c_client * client,char * buf,unsigned int offset,size_t count)74 static 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 if (count > I2C_SMBUS_BLOCK_MAX)
86 count = I2C_SMBUS_BLOCK_MAX;
87
88 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
89 count, buf);
90 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
91
92 return status;
93 }
94
ee1004_read(struct file * filp,struct kobject * kobj,struct bin_attribute * bin_attr,char * buf,loff_t off,size_t count)95 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
96 struct bin_attribute *bin_attr,
97 char *buf, loff_t off, size_t count)
98 {
99 struct device *dev = kobj_to_dev(kobj);
100 struct i2c_client *client = to_i2c_client(dev);
101 size_t requested = count;
102 int page;
103
104 if (unlikely(!count))
105 return count;
106
107 page = off >> EE1004_PAGE_SHIFT;
108 if (unlikely(page > 1))
109 return 0;
110 off &= (1 << EE1004_PAGE_SHIFT) - 1;
111
112 /*
113 * Read data from chip, protecting against concurrent access to
114 * other EE1004 SPD EEPROMs on the same adapter.
115 */
116 mutex_lock(&ee1004_bus_lock);
117
118 while (count) {
119 int status;
120
121 /* Select page */
122 if (page != ee1004_current_page) {
123 /* Data is ignored */
124 status = i2c_smbus_write_byte(ee1004_set_page[page],
125 0x00);
126 if (status == -ENXIO) {
127 /*
128 * Don't give up just yet. Some memory
129 * modules will select the page but not
130 * ack the command. Check which page is
131 * selected now.
132 */
133 if (ee1004_get_current_page() == page)
134 status = 0;
135 }
136 if (status < 0) {
137 dev_err(dev, "Failed to select page %d (%d)\n",
138 page, status);
139 mutex_unlock(&ee1004_bus_lock);
140 return status;
141 }
142 dev_dbg(dev, "Selected page %d\n", page);
143 ee1004_current_page = page;
144 }
145
146 status = ee1004_eeprom_read(client, buf, off, count);
147 if (status < 0) {
148 mutex_unlock(&ee1004_bus_lock);
149 return status;
150 }
151 buf += status;
152 off += status;
153 count -= status;
154
155 if (off == EE1004_PAGE_SIZE) {
156 page++;
157 off = 0;
158 }
159 }
160
161 mutex_unlock(&ee1004_bus_lock);
162
163 return requested;
164 }
165
166 static const struct bin_attribute eeprom_attr = {
167 .attr = {
168 .name = "eeprom",
169 .mode = 0444,
170 },
171 .size = EE1004_EEPROM_SIZE,
172 .read = ee1004_read,
173 };
174
ee1004_probe(struct i2c_client * client,const struct i2c_device_id * id)175 static int ee1004_probe(struct i2c_client *client,
176 const struct i2c_device_id *id)
177 {
178 int err, cnr = 0;
179 const char *slow = NULL;
180
181 /* Make sure we can operate on this adapter */
182 if (!i2c_check_functionality(client->adapter,
183 I2C_FUNC_SMBUS_READ_BYTE |
184 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
185 if (i2c_check_functionality(client->adapter,
186 I2C_FUNC_SMBUS_READ_BYTE |
187 I2C_FUNC_SMBUS_READ_WORD_DATA))
188 slow = "word";
189 else if (i2c_check_functionality(client->adapter,
190 I2C_FUNC_SMBUS_READ_BYTE |
191 I2C_FUNC_SMBUS_READ_BYTE_DATA))
192 slow = "byte";
193 else
194 return -EPFNOSUPPORT;
195 }
196
197 /* Use 2 dummy devices for page select command */
198 mutex_lock(&ee1004_bus_lock);
199 if (++ee1004_dev_count == 1) {
200 for (cnr = 0; cnr < 2; cnr++) {
201 ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
202 EE1004_ADDR_SET_PAGE + cnr);
203 if (IS_ERR(ee1004_set_page[cnr])) {
204 dev_err(&client->dev,
205 "address 0x%02x unavailable\n",
206 EE1004_ADDR_SET_PAGE + cnr);
207 err = PTR_ERR(ee1004_set_page[cnr]);
208 goto err_clients;
209 }
210 }
211 } else if (i2c_adapter_id(client->adapter) !=
212 i2c_adapter_id(ee1004_set_page[0]->adapter)) {
213 dev_err(&client->dev,
214 "Driver only supports devices on a single I2C bus\n");
215 err = -EOPNOTSUPP;
216 goto err_clients;
217 }
218
219 /* Remember current page to avoid unneeded page select */
220 err = ee1004_get_current_page();
221 if (err < 0)
222 goto err_clients;
223 ee1004_current_page = err;
224 dev_dbg(&client->dev, "Currently selected page: %d\n",
225 ee1004_current_page);
226 mutex_unlock(&ee1004_bus_lock);
227
228 /* Create the sysfs eeprom file */
229 err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
230 if (err)
231 goto err_clients_lock;
232
233 dev_info(&client->dev,
234 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
235 EE1004_EEPROM_SIZE);
236 if (slow)
237 dev_notice(&client->dev,
238 "Falling back to %s reads, performance will suffer\n",
239 slow);
240
241 return 0;
242
243 err_clients_lock:
244 mutex_lock(&ee1004_bus_lock);
245 err_clients:
246 if (--ee1004_dev_count == 0) {
247 for (cnr--; cnr >= 0; cnr--) {
248 i2c_unregister_device(ee1004_set_page[cnr]);
249 ee1004_set_page[cnr] = NULL;
250 }
251 }
252 mutex_unlock(&ee1004_bus_lock);
253
254 return err;
255 }
256
ee1004_remove(struct i2c_client * client)257 static int ee1004_remove(struct i2c_client *client)
258 {
259 int i;
260
261 sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
262
263 /* Remove page select clients if this is the last device */
264 mutex_lock(&ee1004_bus_lock);
265 if (--ee1004_dev_count == 0) {
266 for (i = 0; i < 2; i++) {
267 i2c_unregister_device(ee1004_set_page[i]);
268 ee1004_set_page[i] = NULL;
269 }
270 }
271 mutex_unlock(&ee1004_bus_lock);
272
273 return 0;
274 }
275
276 /*-------------------------------------------------------------------------*/
277
278 static struct i2c_driver ee1004_driver = {
279 .driver = {
280 .name = "ee1004",
281 },
282 .probe = ee1004_probe,
283 .remove = ee1004_remove,
284 .id_table = ee1004_ids,
285 };
286 module_i2c_driver(ee1004_driver);
287
288 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
289 MODULE_AUTHOR("Jean Delvare");
290 MODULE_LICENSE("GPL");
291