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/device.h>
13#include <linux/i2c.h>
14#include <linux/init.h>
15#include <linux/kernel.h>
16#include <linux/mod_devicetable.h>
17#include <linux/module.h>
18#include <linux/mutex.h>
19#include <linux/nvmem-provider.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_MAX_BUSSES 8
37#define EE1004_ADDR_SET_PAGE 0x36
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/*
44 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
45 * from page selection to end of read.
46 */
47static DEFINE_MUTEX(ee1004_bus_lock);
48
49static struct ee1004_bus_data {
50 struct i2c_adapter *adap;
51 struct i2c_client *set_page[EE1004_NUM_PAGES];
52 unsigned int dev_count;
53 int current_page;
54} ee1004_bus_data[EE1004_MAX_BUSSES];
55
56static const struct i2c_device_id ee1004_ids[] = {
57 { "ee1004" },
58 { }
59};
60MODULE_DEVICE_TABLE(i2c, ee1004_ids);
61
62/*-------------------------------------------------------------------------*/
63
64static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
65{
66 int i;
67
68 for (i = 0; i < EE1004_MAX_BUSSES; i++)
69 if (ee1004_bus_data[i].adap == adap)
70 return ee1004_bus_data + i;
71
72 /* If not existent yet, create new entry */
73 for (i = 0; i < EE1004_MAX_BUSSES; i++)
74 if (!ee1004_bus_data[i].adap) {
75 ee1004_bus_data[i].adap = adap;
76 return ee1004_bus_data + i;
77 }
78
79 return NULL;
80}
81
82static int ee1004_get_current_page(struct ee1004_bus_data *bd)
83{
84 int err;
85
86 err = i2c_smbus_read_byte(client: bd->set_page[0]);
87 if (err == -ENXIO) {
88 /* Nack means page 1 is selected */
89 return 1;
90 }
91 if (err < 0) {
92 /* Anything else is a real error, bail out */
93 return err;
94 }
95
96 /* Ack means page 0 is selected, returned value meaningless */
97 return 0;
98}
99
100static int ee1004_set_current_page(struct i2c_client *client, int page)
101{
102 struct ee1004_bus_data *bd = i2c_get_clientdata(client);
103 int ret;
104
105 if (page == bd->current_page)
106 return 0;
107
108 /* Data is ignored */
109 ret = i2c_smbus_write_byte(client: bd->set_page[page], value: 0x00);
110 /*
111 * Don't give up just yet. Some memory modules will select the page
112 * but not ack the command. Check which page is selected now.
113 */
114 if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
115 ret = 0;
116 if (ret < 0) {
117 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
118 return ret;
119 }
120
121 dev_dbg(&client->dev, "Selected page %d\n", page);
122 bd->current_page = page;
123
124 return 0;
125}
126
127static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
128 unsigned int offset, size_t count)
129{
130 int status, page;
131
132 page = offset >> EE1004_PAGE_SHIFT;
133 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
134
135 status = ee1004_set_current_page(client, page);
136 if (status)
137 return status;
138
139 /* Can't cross page boundaries */
140 if (offset + count > EE1004_PAGE_SIZE)
141 count = EE1004_PAGE_SIZE - offset;
142
143 if (count > I2C_SMBUS_BLOCK_MAX)
144 count = I2C_SMBUS_BLOCK_MAX;
145
146 return i2c_smbus_read_i2c_block_data_or_emulated(client, command: offset, length: count, values: buf);
147}
148
149static int ee1004_read(void *priv, unsigned int off, void *val, size_t count)
150{
151 struct i2c_client *client = priv;
152 char *buf = val;
153 int ret;
154
155 if (unlikely(!count))
156 return count;
157
158 if (off + count > EE1004_EEPROM_SIZE)
159 return -EINVAL;
160
161 /*
162 * Read data from chip, protecting against concurrent access to
163 * other EE1004 SPD EEPROMs on the same adapter.
164 */
165 mutex_lock(&ee1004_bus_lock);
166
167 while (count) {
168 ret = ee1004_eeprom_read(client, buf, offset: off, count);
169 if (ret < 0) {
170 mutex_unlock(lock: &ee1004_bus_lock);
171 return ret;
172 }
173
174 buf += ret;
175 off += ret;
176 count -= ret;
177 }
178
179 mutex_unlock(lock: &ee1004_bus_lock);
180
181 return 0;
182}
183
184static void ee1004_probe_temp_sensor(struct i2c_client *client)
185{
186 struct i2c_board_info info = { .type = "jc42" };
187 unsigned short addr = 0x18 | (client->addr & 7);
188 unsigned short addr_list[] = { addr, I2C_CLIENT_END };
189 u8 data[2];
190 int ret;
191
192 /* byte 14, bit 7 is set if temp sensor is present */
193 ret = ee1004_eeprom_read(client, buf: data, offset: 14, count: 1);
194 if (ret != 1)
195 return;
196
197 if (!(data[0] & BIT(7))) {
198 /*
199 * If the SPD data suggests that there is no temperature
200 * sensor, it may still be there for SPD revision 1.0.
201 * See SPD Annex L, Revision 1 and 2, for details.
202 * Check DIMM type and SPD revision; if it is a DDR4
203 * with SPD revision 1.0, check the thermal sensor address
204 * and instantiate the jc42 driver if a chip is found at
205 * that address.
206 * It is not necessary to check if there is a chip at the
207 * temperature sensor address since i2c_new_scanned_device()
208 * will do that and return silently if no chip is found.
209 */
210 ret = ee1004_eeprom_read(client, buf: data, offset: 1, count: 2);
211 if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c)
212 return;
213 }
214 i2c_new_scanned_device(adap: client->adapter, info: &info, addr_list, NULL);
215}
216
217static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
218{
219 if (--bd->dev_count == 0) {
220 while (--idx >= 0)
221 i2c_unregister_device(client: bd->set_page[idx]);
222 memset(bd, 0, sizeof(struct ee1004_bus_data));
223 }
224}
225
226static void ee1004_cleanup_bus_data(void *data)
227{
228 struct ee1004_bus_data *bd = data;
229
230 /* Remove page select clients if this is the last device */
231 mutex_lock(&ee1004_bus_lock);
232 ee1004_cleanup(EE1004_NUM_PAGES, bd);
233 mutex_unlock(lock: &ee1004_bus_lock);
234}
235
236static int ee1004_init_bus_data(struct i2c_client *client)
237{
238 struct ee1004_bus_data *bd;
239 int err, cnr = 0;
240
241 bd = ee1004_get_bus_data(adap: client->adapter);
242 if (!bd)
243 return dev_err_probe(dev: &client->dev, err: -ENOSPC, fmt: "Only %d busses supported",
244 EE1004_MAX_BUSSES);
245
246 i2c_set_clientdata(client, data: bd);
247
248 if (++bd->dev_count == 1) {
249 /* Use 2 dummy devices for page select command */
250 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
251 struct i2c_client *cl;
252
253 cl = i2c_new_dummy_device(adapter: client->adapter, EE1004_ADDR_SET_PAGE + cnr);
254 if (IS_ERR(ptr: cl)) {
255 err = PTR_ERR(ptr: cl);
256 goto err_out;
257 }
258
259 bd->set_page[cnr] = cl;
260 }
261
262 /* Remember current page to avoid unneeded page select */
263 err = ee1004_get_current_page(bd);
264 if (err < 0)
265 goto err_out;
266
267 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
268 bd->current_page = err;
269 }
270
271 return 0;
272
273err_out:
274 ee1004_cleanup(idx: cnr, bd);
275
276 return err;
277}
278
279static int ee1004_probe(struct i2c_client *client)
280{
281 struct nvmem_config config = {
282 .dev = &client->dev,
283 .name = dev_name(dev: &client->dev),
284 .id = NVMEM_DEVID_NONE,
285 .owner = THIS_MODULE,
286 .type = NVMEM_TYPE_EEPROM,
287 .read_only = true,
288 .root_only = false,
289 .reg_read = ee1004_read,
290 .size = EE1004_EEPROM_SIZE,
291 .word_size = 1,
292 .stride = 1,
293 .priv = client,
294 .compat = true,
295 .base_dev = &client->dev,
296 };
297 struct nvmem_device *ndev;
298 int err;
299
300 /* Make sure we can operate on this adapter */
301 if (!i2c_check_functionality(adap: client->adapter,
302 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
303 !i2c_check_functionality(adap: client->adapter,
304 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
305 return -EPFNOSUPPORT;
306
307 err = i2c_smbus_read_byte(client);
308 if (err < 0)
309 return -ENODEV;
310
311 mutex_lock(&ee1004_bus_lock);
312
313 err = ee1004_init_bus_data(client);
314 if (err < 0) {
315 mutex_unlock(lock: &ee1004_bus_lock);
316 return err;
317 }
318
319 ee1004_probe_temp_sensor(client);
320
321 mutex_unlock(lock: &ee1004_bus_lock);
322
323 err = devm_add_action_or_reset(&client->dev, ee1004_cleanup_bus_data,
324 i2c_get_clientdata(client));
325 if (err < 0)
326 return err;
327
328 ndev = devm_nvmem_register(dev: &client->dev, cfg: &config);
329 if (IS_ERR(ptr: ndev))
330 return PTR_ERR(ptr: ndev);
331
332 dev_info(&client->dev,
333 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
334 EE1004_EEPROM_SIZE);
335
336 return 0;
337}
338
339/*-------------------------------------------------------------------------*/
340
341static struct i2c_driver ee1004_driver = {
342 .driver = {
343 .name = "ee1004",
344 },
345 .probe = ee1004_probe,
346 .id_table = ee1004_ids,
347};
348module_i2c_driver(ee1004_driver);
349
350MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
351MODULE_AUTHOR("Jean Delvare");
352MODULE_LICENSE("GPL");
353

source code of linux/drivers/misc/eeprom/ee1004.c