1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * ee1004 - driver for DDR4 SPD EEPROMs
5 * Copyright (C) 2017-2019 Jean Delvare
7 * Based on the at24 driver:
8 * Copyright (C) 2005-2007 David Brownell
9 * Copyright (C) 2008 Wolfram Sang, Pengutronix
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>
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.
25 * Therefore we need to request these 2 additional addresses, and serialize
26 * access to all such EEPROMs with a single mutex.
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
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)
42 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
43 * from page selection to end of read.
45 static DEFINE_MUTEX(ee1004_bus_lock);
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;
52 } ee1004_bus_data[EE1004_MAX_BUSSES];
54 static const struct i2c_device_id ee1004_ids[] = {
58 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
60 /*-------------------------------------------------------------------------*/
62 static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
66 for (i = 0; i < EE1004_MAX_BUSSES; i++)
67 if (ee1004_bus_data[i].adap == adap)
68 return ee1004_bus_data + i;
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;
80 static int ee1004_get_current_page(struct ee1004_bus_data *bd)
84 err = i2c_smbus_read_byte(bd->set_page[0]);
86 /* Nack means page 1 is selected */
90 /* Anything else is a real error, bail out */
94 /* Ack means page 0 is selected, returned value meaningless */
98 static int ee1004_set_current_page(struct i2c_client *client, int page)
100 struct ee1004_bus_data *bd = i2c_get_clientdata(client);
103 if (page == bd->current_page)
106 /* Data is ignored */
107 ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
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.
112 if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
115 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
119 dev_dbg(&client->dev, "Selected page %d\n", page);
120 bd->current_page = page;
125 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
126 unsigned int offset, size_t count)
130 page = offset >> EE1004_PAGE_SHIFT;
131 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
133 status = ee1004_set_current_page(client, page);
137 /* Can't cross page boundaries */
138 if (offset + count > EE1004_PAGE_SIZE)
139 count = EE1004_PAGE_SIZE - offset;
141 if (count > I2C_SMBUS_BLOCK_MAX)
142 count = I2C_SMBUS_BLOCK_MAX;
144 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
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)
151 struct i2c_client *client = kobj_to_i2c_client(kobj);
152 size_t requested = count;
156 * Read data from chip, protecting against concurrent access to
157 * other EE1004 SPD EEPROMs on the same adapter.
159 mutex_lock(&ee1004_bus_lock);
162 ret = ee1004_eeprom_read(client, buf, off, count);
171 mutex_unlock(&ee1004_bus_lock);
173 return ret < 0 ? ret : requested;
176 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
178 static struct bin_attribute *ee1004_attrs[] = {
183 BIN_ATTRIBUTE_GROUPS(ee1004);
185 static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
187 if (--bd->dev_count == 0) {
189 i2c_unregister_device(bd->set_page[idx]);
190 memset(bd, 0, sizeof(struct ee1004_bus_data));
194 static int ee1004_probe(struct i2c_client *client)
196 struct ee1004_bus_data *bd;
199 /* Make sure we can operate on this adapter */
200 if (!i2c_check_functionality(client->adapter,
201 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
202 !i2c_check_functionality(client->adapter,
203 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
204 return -EPFNOSUPPORT;
206 mutex_lock(&ee1004_bus_lock);
208 bd = ee1004_get_bus_data(client->adapter);
210 mutex_unlock(&ee1004_bus_lock);
211 return dev_err_probe(&client->dev, -ENOSPC,
212 "Only %d busses supported", EE1004_MAX_BUSSES);
215 i2c_set_clientdata(client, bd);
217 if (++bd->dev_count == 1) {
218 /* Use 2 dummy devices for page select command */
219 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
220 struct i2c_client *cl;
222 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
227 bd->set_page[cnr] = cl;
230 /* Remember current page to avoid unneeded page select */
231 err = ee1004_get_current_page(bd);
234 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
235 bd->current_page = err;
237 mutex_unlock(&ee1004_bus_lock);
239 dev_info(&client->dev,
240 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
246 ee1004_cleanup(cnr, bd);
247 mutex_unlock(&ee1004_bus_lock);
252 static void ee1004_remove(struct i2c_client *client)
254 struct ee1004_bus_data *bd = i2c_get_clientdata(client);
256 /* Remove page select clients if this is the last device */
257 mutex_lock(&ee1004_bus_lock);
258 ee1004_cleanup(EE1004_NUM_PAGES, bd);
259 mutex_unlock(&ee1004_bus_lock);
262 /*-------------------------------------------------------------------------*/
264 static struct i2c_driver ee1004_driver = {
267 .dev_groups = ee1004_groups,
269 .probe = ee1004_probe,
270 .remove = ee1004_remove,
271 .id_table = ee1004_ids,
273 module_i2c_driver(ee1004_driver);
275 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
276 MODULE_AUTHOR("Jean Delvare");
277 MODULE_LICENSE("GPL");