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_MAX_BUSSES 8
35 #define EE1004_ADDR_SET_PAGE 0x36
36 #define EE1004_NUM_PAGES 2
37 #define EE1004_PAGE_SIZE 256
38 #define EE1004_PAGE_SHIFT 8
39 #define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
40
41 /*
42 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
43 * from page selection to end of read.
44 */
45 static DEFINE_MUTEX(ee1004_bus_lock);
46
47 static struct ee1004_bus_data {
48 struct i2c_adapter *adap;
49 struct i2c_client *set_page[EE1004_NUM_PAGES];
50 unsigned int dev_count;
51 int current_page;
52 } ee1004_bus_data[EE1004_MAX_BUSSES];
53
54 static const struct i2c_device_id ee1004_ids[] = {
55 { "ee1004", 0 },
56 { }
57 };
58 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
59
60 /*-------------------------------------------------------------------------*/
61
ee1004_get_bus_data(struct i2c_adapter * adap)62 static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
63 {
64 int i;
65
66 for (i = 0; i < EE1004_MAX_BUSSES; i++)
67 if (ee1004_bus_data[i].adap == adap)
68 return ee1004_bus_data + i;
69
70 /* If not existent yet, create new entry */
71 for (i = 0; i < EE1004_MAX_BUSSES; i++)
72 if (!ee1004_bus_data[i].adap) {
73 ee1004_bus_data[i].adap = adap;
74 return ee1004_bus_data + i;
75 }
76
77 return NULL;
78 }
79
ee1004_get_current_page(struct ee1004_bus_data * bd)80 static int ee1004_get_current_page(struct ee1004_bus_data *bd)
81 {
82 int err;
83
84 err = i2c_smbus_read_byte(bd->set_page[0]);
85 if (err == -ENXIO) {
86 /* Nack means page 1 is selected */
87 return 1;
88 }
89 if (err < 0) {
90 /* Anything else is a real error, bail out */
91 return err;
92 }
93
94 /* Ack means page 0 is selected, returned value meaningless */
95 return 0;
96 }
97
ee1004_set_current_page(struct i2c_client * client,int page)98 static int ee1004_set_current_page(struct i2c_client *client, int page)
99 {
100 struct ee1004_bus_data *bd = i2c_get_clientdata(client);
101 int ret;
102
103 if (page == bd->current_page)
104 return 0;
105
106 /* Data is ignored */
107 ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
108 /*
109 * Don't give up just yet. Some memory modules will select the page
110 * but not ack the command. Check which page is selected now.
111 */
112 if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
113 ret = 0;
114 if (ret < 0) {
115 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
116 return ret;
117 }
118
119 dev_dbg(&client->dev, "Selected page %d\n", page);
120 bd->current_page = page;
121
122 return 0;
123 }
124
ee1004_eeprom_read(struct i2c_client * client,char * buf,unsigned int offset,size_t count)125 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
126 unsigned int offset, size_t count)
127 {
128 int status, page;
129
130 page = offset >> EE1004_PAGE_SHIFT;
131 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
132
133 status = ee1004_set_current_page(client, page);
134 if (status)
135 return status;
136
137 /* Can't cross page boundaries */
138 if (offset + count > EE1004_PAGE_SIZE)
139 count = EE1004_PAGE_SIZE - offset;
140
141 if (count > I2C_SMBUS_BLOCK_MAX)
142 count = I2C_SMBUS_BLOCK_MAX;
143
144 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
145 }
146
eeprom_read(struct file * filp,struct kobject * kobj,struct bin_attribute * bin_attr,char * buf,loff_t off,size_t count)147 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
148 struct bin_attribute *bin_attr,
149 char *buf, loff_t off, size_t count)
150 {
151 struct i2c_client *client = kobj_to_i2c_client(kobj);
152 size_t requested = count;
153 int ret = 0;
154
155 /*
156 * Read data from chip, protecting against concurrent access to
157 * other EE1004 SPD EEPROMs on the same adapter.
158 */
159 mutex_lock(&ee1004_bus_lock);
160
161 while (count) {
162 ret = ee1004_eeprom_read(client, buf, off, count);
163 if (ret < 0)
164 goto out;
165
166 buf += ret;
167 off += ret;
168 count -= ret;
169 }
170 out:
171 mutex_unlock(&ee1004_bus_lock);
172
173 return ret < 0 ? ret : requested;
174 }
175
176 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
177
178 static struct bin_attribute *ee1004_attrs[] = {
179 &bin_attr_eeprom,
180 NULL
181 };
182
183 BIN_ATTRIBUTE_GROUPS(ee1004);
184
ee1004_probe_temp_sensor(struct i2c_client * client)185 static void ee1004_probe_temp_sensor(struct i2c_client *client)
186 {
187 struct i2c_board_info info = { .type = "jc42" };
188 u8 byte14;
189 int ret;
190
191 /* byte 14, bit 7 is set if temp sensor is present */
192 ret = ee1004_eeprom_read(client, &byte14, 14, 1);
193 if (ret != 1 || !(byte14 & BIT(7)))
194 return;
195
196 info.addr = 0x18 | (client->addr & 7);
197
198 i2c_new_client_device(client->adapter, &info);
199 }
200
ee1004_cleanup(int idx,struct ee1004_bus_data * bd)201 static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
202 {
203 if (--bd->dev_count == 0) {
204 while (--idx >= 0)
205 i2c_unregister_device(bd->set_page[idx]);
206 memset(bd, 0, sizeof(struct ee1004_bus_data));
207 }
208 }
209
ee1004_probe(struct i2c_client * client)210 static int ee1004_probe(struct i2c_client *client)
211 {
212 struct ee1004_bus_data *bd;
213 int err, cnr = 0;
214
215 /* Make sure we can operate on this adapter */
216 if (!i2c_check_functionality(client->adapter,
217 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
218 !i2c_check_functionality(client->adapter,
219 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
220 return -EPFNOSUPPORT;
221
222 mutex_lock(&ee1004_bus_lock);
223
224 bd = ee1004_get_bus_data(client->adapter);
225 if (!bd) {
226 mutex_unlock(&ee1004_bus_lock);
227 return dev_err_probe(&client->dev, -ENOSPC,
228 "Only %d busses supported", EE1004_MAX_BUSSES);
229 }
230
231 i2c_set_clientdata(client, bd);
232
233 if (++bd->dev_count == 1) {
234 /* Use 2 dummy devices for page select command */
235 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
236 struct i2c_client *cl;
237
238 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
239 if (IS_ERR(cl)) {
240 err = PTR_ERR(cl);
241 goto err_clients;
242 }
243 bd->set_page[cnr] = cl;
244 }
245
246 /* Remember current page to avoid unneeded page select */
247 err = ee1004_get_current_page(bd);
248 if (err < 0)
249 goto err_clients;
250 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
251 bd->current_page = err;
252 }
253
254 ee1004_probe_temp_sensor(client);
255
256 mutex_unlock(&ee1004_bus_lock);
257
258 dev_info(&client->dev,
259 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
260 EE1004_EEPROM_SIZE);
261
262 return 0;
263
264 err_clients:
265 ee1004_cleanup(cnr, bd);
266 mutex_unlock(&ee1004_bus_lock);
267
268 return err;
269 }
270
ee1004_remove(struct i2c_client * client)271 static void ee1004_remove(struct i2c_client *client)
272 {
273 struct ee1004_bus_data *bd = i2c_get_clientdata(client);
274
275 /* Remove page select clients if this is the last device */
276 mutex_lock(&ee1004_bus_lock);
277 ee1004_cleanup(EE1004_NUM_PAGES, bd);
278 mutex_unlock(&ee1004_bus_lock);
279 }
280
281 /*-------------------------------------------------------------------------*/
282
283 static struct i2c_driver ee1004_driver = {
284 .driver = {
285 .name = "ee1004",
286 .dev_groups = ee1004_groups,
287 },
288 .probe = ee1004_probe,
289 .remove = ee1004_remove,
290 .id_table = ee1004_ids,
291 };
292 module_i2c_driver(ee1004_driver);
293
294 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
295 MODULE_AUTHOR("Jean Delvare");
296 MODULE_LICENSE("GPL");
297