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2874c5fd | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
3b7584a2 JD |
2 | /* |
3 | * ee1004 - driver for DDR4 SPD EEPROMs | |
4 | * | |
5 | * Copyright (C) 2017 Jean Delvare | |
6 | * | |
7 | * Based on the at24 driver: | |
8 | * Copyright (C) 2005-2007 David Brownell | |
9 | * Copyright (C) 2008 Wolfram Sang, Pengutronix | |
3b7584a2 JD |
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 | ||
56 | static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, | |
57 | unsigned int offset, size_t count) | |
58 | { | |
59 | int status; | |
60 | ||
61 | if (count > I2C_SMBUS_BLOCK_MAX) | |
62 | count = I2C_SMBUS_BLOCK_MAX; | |
63 | /* Can't cross page boundaries */ | |
64 | if (unlikely(offset + count > EE1004_PAGE_SIZE)) | |
65 | count = EE1004_PAGE_SIZE - offset; | |
66 | ||
67 | status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, | |
68 | count, buf); | |
69 | dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); | |
70 | ||
71 | return status; | |
72 | } | |
73 | ||
74 | static ssize_t ee1004_read(struct file *filp, struct kobject *kobj, | |
75 | struct bin_attribute *bin_attr, | |
76 | char *buf, loff_t off, size_t count) | |
77 | { | |
78 | struct device *dev = kobj_to_dev(kobj); | |
79 | struct i2c_client *client = to_i2c_client(dev); | |
80 | size_t requested = count; | |
81 | int page; | |
82 | ||
83 | if (unlikely(!count)) | |
84 | return count; | |
85 | ||
86 | page = off >> EE1004_PAGE_SHIFT; | |
87 | if (unlikely(page > 1)) | |
88 | return 0; | |
89 | off &= (1 << EE1004_PAGE_SHIFT) - 1; | |
90 | ||
91 | /* | |
92 | * Read data from chip, protecting against concurrent access to | |
93 | * other EE1004 SPD EEPROMs on the same adapter. | |
94 | */ | |
95 | mutex_lock(&ee1004_bus_lock); | |
96 | ||
97 | while (count) { | |
98 | int status; | |
99 | ||
100 | /* Select page */ | |
101 | if (page != ee1004_current_page) { | |
102 | /* Data is ignored */ | |
103 | status = i2c_smbus_write_byte(ee1004_set_page[page], | |
104 | 0x00); | |
105 | if (status < 0) { | |
106 | dev_err(dev, "Failed to select page %d (%d)\n", | |
107 | page, status); | |
108 | mutex_unlock(&ee1004_bus_lock); | |
109 | return status; | |
110 | } | |
111 | dev_dbg(dev, "Selected page %d\n", page); | |
112 | ee1004_current_page = page; | |
113 | } | |
114 | ||
115 | status = ee1004_eeprom_read(client, buf, off, count); | |
116 | if (status < 0) { | |
117 | mutex_unlock(&ee1004_bus_lock); | |
118 | return status; | |
119 | } | |
120 | buf += status; | |
121 | off += status; | |
122 | count -= status; | |
123 | ||
124 | if (off == EE1004_PAGE_SIZE) { | |
125 | page++; | |
126 | off = 0; | |
127 | } | |
128 | } | |
129 | ||
130 | mutex_unlock(&ee1004_bus_lock); | |
131 | ||
132 | return requested; | |
133 | } | |
134 | ||
135 | static const struct bin_attribute eeprom_attr = { | |
136 | .attr = { | |
137 | .name = "eeprom", | |
138 | .mode = 0444, | |
139 | }, | |
140 | .size = EE1004_EEPROM_SIZE, | |
141 | .read = ee1004_read, | |
142 | }; | |
143 | ||
144 | static int ee1004_probe(struct i2c_client *client, | |
145 | const struct i2c_device_id *id) | |
146 | { | |
147 | int err, cnr = 0; | |
148 | const char *slow = NULL; | |
149 | ||
150 | /* Make sure we can operate on this adapter */ | |
151 | if (!i2c_check_functionality(client->adapter, | |
152 | I2C_FUNC_SMBUS_READ_BYTE | | |
153 | I2C_FUNC_SMBUS_READ_I2C_BLOCK)) { | |
154 | if (i2c_check_functionality(client->adapter, | |
155 | I2C_FUNC_SMBUS_READ_BYTE | | |
156 | I2C_FUNC_SMBUS_READ_WORD_DATA)) | |
157 | slow = "word"; | |
158 | else if (i2c_check_functionality(client->adapter, | |
159 | I2C_FUNC_SMBUS_READ_BYTE | | |
160 | I2C_FUNC_SMBUS_READ_BYTE_DATA)) | |
161 | slow = "byte"; | |
162 | else | |
163 | return -EPFNOSUPPORT; | |
164 | } | |
165 | ||
166 | /* Use 2 dummy devices for page select command */ | |
167 | mutex_lock(&ee1004_bus_lock); | |
168 | if (++ee1004_dev_count == 1) { | |
169 | for (cnr = 0; cnr < 2; cnr++) { | |
170 | ee1004_set_page[cnr] = i2c_new_dummy(client->adapter, | |
171 | EE1004_ADDR_SET_PAGE + cnr); | |
172 | if (!ee1004_set_page[cnr]) { | |
173 | dev_err(&client->dev, | |
174 | "address 0x%02x unavailable\n", | |
175 | EE1004_ADDR_SET_PAGE + cnr); | |
176 | err = -EADDRINUSE; | |
177 | goto err_clients; | |
178 | } | |
179 | } | |
180 | } else if (i2c_adapter_id(client->adapter) != | |
181 | i2c_adapter_id(ee1004_set_page[0]->adapter)) { | |
182 | dev_err(&client->dev, | |
183 | "Driver only supports devices on a single I2C bus\n"); | |
184 | err = -EOPNOTSUPP; | |
185 | goto err_clients; | |
186 | } | |
187 | ||
188 | /* Remember current page to avoid unneeded page select */ | |
189 | err = i2c_smbus_read_byte(ee1004_set_page[0]); | |
190 | if (err == -ENXIO) { | |
191 | /* Nack means page 1 is selected */ | |
192 | ee1004_current_page = 1; | |
193 | } else if (err < 0) { | |
194 | /* Anything else is a real error, bail out */ | |
195 | goto err_clients; | |
196 | } else { | |
197 | /* Ack means page 0 is selected, returned value meaningless */ | |
198 | ee1004_current_page = 0; | |
199 | } | |
200 | dev_dbg(&client->dev, "Currently selected page: %d\n", | |
201 | ee1004_current_page); | |
202 | mutex_unlock(&ee1004_bus_lock); | |
203 | ||
204 | /* Create the sysfs eeprom file */ | |
205 | err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr); | |
206 | if (err) | |
207 | goto err_clients_lock; | |
208 | ||
209 | dev_info(&client->dev, | |
210 | "%u byte EE1004-compliant SPD EEPROM, read-only\n", | |
211 | EE1004_EEPROM_SIZE); | |
212 | if (slow) | |
213 | dev_notice(&client->dev, | |
214 | "Falling back to %s reads, performance will suffer\n", | |
215 | slow); | |
216 | ||
217 | return 0; | |
218 | ||
219 | err_clients_lock: | |
220 | mutex_lock(&ee1004_bus_lock); | |
221 | err_clients: | |
222 | if (--ee1004_dev_count == 0) { | |
223 | for (cnr--; cnr >= 0; cnr--) { | |
224 | i2c_unregister_device(ee1004_set_page[cnr]); | |
225 | ee1004_set_page[cnr] = NULL; | |
226 | } | |
227 | } | |
228 | mutex_unlock(&ee1004_bus_lock); | |
229 | ||
230 | return err; | |
231 | } | |
232 | ||
233 | static int ee1004_remove(struct i2c_client *client) | |
234 | { | |
235 | int i; | |
236 | ||
237 | sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr); | |
238 | ||
239 | /* Remove page select clients if this is the last device */ | |
240 | mutex_lock(&ee1004_bus_lock); | |
241 | if (--ee1004_dev_count == 0) { | |
242 | for (i = 0; i < 2; i++) { | |
243 | i2c_unregister_device(ee1004_set_page[i]); | |
244 | ee1004_set_page[i] = NULL; | |
245 | } | |
246 | } | |
247 | mutex_unlock(&ee1004_bus_lock); | |
248 | ||
249 | return 0; | |
250 | } | |
251 | ||
252 | /*-------------------------------------------------------------------------*/ | |
253 | ||
254 | static struct i2c_driver ee1004_driver = { | |
255 | .driver = { | |
256 | .name = "ee1004", | |
257 | }, | |
258 | .probe = ee1004_probe, | |
259 | .remove = ee1004_remove, | |
260 | .id_table = ee1004_ids, | |
261 | }; | |
262 | ||
263 | static int __init ee1004_init(void) | |
264 | { | |
265 | return i2c_add_driver(&ee1004_driver); | |
266 | } | |
267 | module_init(ee1004_init); | |
268 | ||
269 | static void __exit ee1004_exit(void) | |
270 | { | |
271 | i2c_del_driver(&ee1004_driver); | |
272 | } | |
273 | module_exit(ee1004_exit); | |
274 | ||
275 | MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); | |
276 | MODULE_AUTHOR("Jean Delvare"); | |
277 | MODULE_LICENSE("GPL"); |