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_ADDR_SET_PAGE 0x36
35 #define EE1004_NUM_PAGES 2
36 #define EE1004_PAGE_SIZE 256
37 #define EE1004_PAGE_SHIFT 8
38 #define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
41 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
42 * from page selection to end of read.
44 static DEFINE_MUTEX(ee1004_bus_lock);
45 static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
46 static unsigned int ee1004_dev_count;
47 static int ee1004_current_page;
49 static const struct i2c_device_id ee1004_ids[] = {
53 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
55 /*-------------------------------------------------------------------------*/
57 static int ee1004_get_current_page(void)
61 err = i2c_smbus_read_byte(ee1004_set_page[0]);
63 /* Nack means page 1 is selected */
67 /* Anything else is a real error, bail out */
71 /* Ack means page 0 is selected, returned value meaningless */
75 static int ee1004_set_current_page(struct device *dev, int page)
79 if (page == ee1004_current_page)
83 ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
85 * Don't give up just yet. Some memory modules will select the page
86 * but not ack the command. Check which page is selected now.
88 if (ret == -ENXIO && ee1004_get_current_page() == page)
91 dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
95 dev_dbg(dev, "Selected page %d\n", page);
96 ee1004_current_page = page;
101 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
102 unsigned int offset, size_t count)
106 page = offset >> EE1004_PAGE_SHIFT;
107 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
109 status = ee1004_set_current_page(&client->dev, page);
113 /* Can't cross page boundaries */
114 if (offset + count > EE1004_PAGE_SIZE)
115 count = EE1004_PAGE_SIZE - offset;
117 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
120 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
121 struct bin_attribute *bin_attr,
122 char *buf, loff_t off, size_t count)
124 struct i2c_client *client = kobj_to_i2c_client(kobj);
125 size_t requested = count;
129 * Read data from chip, protecting against concurrent access to
130 * other EE1004 SPD EEPROMs on the same adapter.
132 mutex_lock(&ee1004_bus_lock);
135 ret = ee1004_eeprom_read(client, buf, off, count);
144 mutex_unlock(&ee1004_bus_lock);
146 return ret < 0 ? ret : requested;
149 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
151 static struct bin_attribute *ee1004_attrs[] = {
156 BIN_ATTRIBUTE_GROUPS(ee1004);
158 static void ee1004_cleanup(int idx)
160 if (--ee1004_dev_count == 0)
162 i2c_unregister_device(ee1004_set_page[idx]);
163 ee1004_set_page[idx] = NULL;
167 static int ee1004_probe(struct i2c_client *client)
171 /* Make sure we can operate on this adapter */
172 if (!i2c_check_functionality(client->adapter,
173 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
174 !i2c_check_functionality(client->adapter,
175 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
176 return -EPFNOSUPPORT;
178 /* Use 2 dummy devices for page select command */
179 mutex_lock(&ee1004_bus_lock);
180 if (++ee1004_dev_count == 1) {
181 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
182 struct i2c_client *cl;
184 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
189 ee1004_set_page[cnr] = cl;
192 /* Remember current page to avoid unneeded page select */
193 err = ee1004_get_current_page();
196 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
197 ee1004_current_page = err;
198 } else if (client->adapter != ee1004_set_page[0]->adapter) {
199 dev_err(&client->dev,
200 "Driver only supports devices on a single I2C bus\n");
204 mutex_unlock(&ee1004_bus_lock);
206 dev_info(&client->dev,
207 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
214 mutex_unlock(&ee1004_bus_lock);
219 static int ee1004_remove(struct i2c_client *client)
221 /* Remove page select clients if this is the last device */
222 mutex_lock(&ee1004_bus_lock);
223 ee1004_cleanup(EE1004_NUM_PAGES);
224 mutex_unlock(&ee1004_bus_lock);
229 /*-------------------------------------------------------------------------*/
231 static struct i2c_driver ee1004_driver = {
234 .dev_groups = ee1004_groups,
236 .probe_new = ee1004_probe,
237 .remove = ee1004_remove,
238 .id_table = ee1004_ids,
240 module_i2c_driver(ee1004_driver);
242 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
243 MODULE_AUTHOR("Jean Delvare");
244 MODULE_LICENSE("GPL");