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/err.h>
13 #include <linux/i2c.h>
14 #include <linux/init.h>
15 #include <linux/kernel.h>
16 #include <linux/list.h>
17 #include <linux/mod_devicetable.h>
18 #include <linux/module.h>
19 #include <linux/mutex.h>
20
21 /*
22 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
23 * specification. These are 512-byte EEPROMs using a single I2C address
24 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
25 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
26 *
27 * Therefore we need to request these 2 additional addresses, and serialize
28 * access to all such EEPROMs with a single mutex.
29 *
30 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
31 * We use SMBus access even if I2C is available, these EEPROMs are small
32 * enough, and reading from them infrequent enough, that we favor simplicity
33 * over performance.
34 */
35
36 #define EE1004_ADDR_SET_PAGE0 0x36
37 #define EE1004_ADDR_SET_PAGE1 0x37
38 #define EE1004_NUM_PAGES 2
39 #define EE1004_PAGE_SIZE 256
40 #define EE1004_PAGE_SHIFT 8
41 #define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
42
43 struct ee1004_bus {
44 struct kref kref;
45 struct list_head list;
46 struct mutex lock;
47 struct i2c_adapter *adapter;
48 struct i2c_client *set_page_clients[EE1004_NUM_PAGES];
49 int page;
50 };
51
52 static LIST_HEAD(ee1004_busses);
53 static DEFINE_MUTEX(ee1004_busses_lock);
54
55 static const struct i2c_device_id ee1004_ids[] = {
56 { "ee1004", 0 },
57 { }
58 };
59 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
60
61 static const struct of_device_id ee1004_of_match[] = {
62 { .compatible = "atmel,at30tse004a" },
63 {}
64 };
65 MODULE_DEVICE_TABLE(of, ee1004_of_match);
66
67 /*-------------------------------------------------------------------------*/
68
ee1004_get_current_page(struct ee1004_bus * bus)69 static int ee1004_get_current_page(struct ee1004_bus *bus)
70 {
71 int err;
72
73 err = i2c_smbus_read_byte(bus->set_page_clients[0]);
74 if (err == -ENXIO) {
75 /* Nack means page 1 is selected */
76 return 1;
77 }
78 if (err < 0) {
79 /* Anything else is a real error, bail out */
80 return err;
81 }
82
83 /* Ack means page 0 is selected, returned value meaningless */
84 return 0;
85 }
86
ee1004_set_current_page(struct ee1004_bus * bus,int page)87 static int ee1004_set_current_page(struct ee1004_bus *bus, int page)
88 {
89 int ret;
90
91 if (page == bus->page)
92 return 0;
93
94 /* Data is ignored */
95 ret = i2c_smbus_write_byte(bus->set_page_clients[page], 0x00);
96
97 /*
98 * Don't give up just yet. Some memory modules will select the page
99 * but not ack the command. Check which page is selected now.
100 */
101 if (ret == -ENXIO && ee1004_get_current_page(bus) == page)
102 ret = 0;
103 if (ret < 0)
104 return ret;
105
106 bus->page = page;
107 return 0;
108 }
109
ee1004_eeprom_read(struct i2c_client * client,struct ee1004_bus * bus,char * buf,unsigned int offset,size_t count)110 static ssize_t ee1004_eeprom_read(struct i2c_client *client, struct ee1004_bus *bus, char *buf,
111 unsigned int offset, size_t count)
112 {
113 int status, page;
114
115 page = offset >> EE1004_PAGE_SHIFT;
116 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
117
118 status = ee1004_set_current_page(bus, page);
119 if (status) {
120 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, status);
121 return status;
122 }
123
124 /* Can't cross page boundaries */
125 if (offset + count > EE1004_PAGE_SIZE)
126 count = EE1004_PAGE_SIZE - offset;
127
128 if (count > I2C_SMBUS_BLOCK_MAX)
129 count = I2C_SMBUS_BLOCK_MAX;
130
131 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
132 }
133
eeprom_read(struct file * filp,struct kobject * kobj,struct bin_attribute * bin_attr,char * buf,loff_t off,size_t count)134 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
135 struct bin_attribute *bin_attr,
136 char *buf, loff_t off, size_t count)
137 {
138 struct i2c_client *client = kobj_to_i2c_client(kobj);
139 struct ee1004_bus *bus = i2c_get_clientdata(client);
140 size_t requested = count;
141 int ret = 0;
142
143 /*
144 * Read data from chip, protecting against concurrent access to
145 * other EE1004 SPD EEPROMs on the same adapter.
146 */
147 mutex_lock(&bus->lock);
148
149 while (count) {
150 ret = ee1004_eeprom_read(client, bus, buf, off, count);
151 if (ret < 0)
152 goto out;
153
154 buf += ret;
155 off += ret;
156 count -= ret;
157 }
158 out:
159 mutex_unlock(&bus->lock);
160
161 return ret < 0 ? ret : requested;
162 }
163
164 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
165
166 static struct bin_attribute *ee1004_attrs[] = {
167 &bin_attr_eeprom,
168 NULL
169 };
170
171 BIN_ATTRIBUTE_GROUPS(ee1004);
172
ee1004_bus_unregister(struct ee1004_bus * bus)173 static void ee1004_bus_unregister(struct ee1004_bus *bus)
174 {
175 i2c_unregister_device(bus->set_page_clients[1]);
176 i2c_unregister_device(bus->set_page_clients[0]);
177 }
178
ee1004_bus_release(struct kref * kref)179 static void ee1004_bus_release(struct kref *kref)
180 {
181 struct ee1004_bus *bus = container_of(kref, struct ee1004_bus, kref);
182
183 ee1004_bus_unregister(bus);
184
185 mutex_lock(&ee1004_busses_lock);
186 list_del(&bus->list);
187 mutex_unlock(&ee1004_busses_lock);
188
189 kfree(bus);
190 }
191
ee1004_bus_initialize(struct ee1004_bus * bus,struct i2c_adapter * adapter)192 static int ee1004_bus_initialize(struct ee1004_bus *bus, struct i2c_adapter *adapter)
193 {
194 bus->set_page_clients[0] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE0);
195 if (IS_ERR(bus->set_page_clients[0]))
196 return PTR_ERR(bus->set_page_clients[0]);
197
198 bus->set_page_clients[1] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE1);
199 if (IS_ERR(bus->set_page_clients[1])) {
200 i2c_unregister_device(bus->set_page_clients[0]);
201 return PTR_ERR(bus->set_page_clients[1]);
202 }
203
204 bus->page = ee1004_get_current_page(bus);
205 if (bus->page < 0) {
206 ee1004_bus_unregister(bus);
207 return bus->page;
208 }
209
210 kref_init(&bus->kref);
211 list_add(&bus->list, &ee1004_busses);
212 mutex_init(&bus->lock);
213 bus->adapter = adapter;
214
215 return 0;
216 }
217
ee1004_probe(struct i2c_client * client)218 static int ee1004_probe(struct i2c_client *client)
219 {
220 struct ee1004_bus *bus;
221 bool found = false;
222 int rc = 0;
223
224 /* Make sure we can operate on this adapter */
225 if (!i2c_check_functionality(client->adapter,
226 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
227 !i2c_check_functionality(client->adapter,
228 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
229 return -EPFNOSUPPORT;
230
231 mutex_lock(&ee1004_busses_lock);
232 list_for_each_entry(bus, &ee1004_busses, list) {
233 if (bus->adapter == client->adapter) {
234 kref_get(&bus->kref);
235 found = true;
236 break;
237 }
238 }
239
240 if (!found) {
241 bus = kzalloc(sizeof(*bus), GFP_KERNEL);
242 if (!bus) {
243 rc = -ENOMEM;
244 goto unlock;
245 }
246
247 rc = ee1004_bus_initialize(bus, client->adapter);
248 if (rc) {
249 kfree(bus);
250 goto unlock;
251 }
252 }
253
254 i2c_set_clientdata(client, bus);
255
256 dev_info(&client->dev,
257 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
258 EE1004_EEPROM_SIZE);
259
260 unlock:
261 mutex_unlock(&ee1004_busses_lock);
262 return rc;
263 }
264
ee1004_remove(struct i2c_client * client)265 static void ee1004_remove(struct i2c_client *client)
266 {
267 struct ee1004_bus *bus = i2c_get_clientdata(client);
268
269 kref_put(&bus->kref, ee1004_bus_release);
270 }
271
272 /*-------------------------------------------------------------------------*/
273
274 static struct i2c_driver ee1004_driver = {
275 .driver = {
276 .name = "ee1004",
277 .dev_groups = ee1004_groups,
278 .of_match_table = ee1004_of_match,
279 },
280 .probe = ee1004_probe,
281 .remove = ee1004_remove,
282 .id_table = ee1004_ids,
283 };
284 module_i2c_driver(ee1004_driver);
285
286 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
287 MODULE_AUTHOR("Jean Delvare");
288 MODULE_LICENSE("GPL");
289