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/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_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)
39
40 /*
41 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
42 * from page selection to end of read.
43 */
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;
48
49 static const struct i2c_device_id ee1004_ids[] = {
50 { "ee1004", 0 },
51 { }
52 };
53 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
54
55 /*-------------------------------------------------------------------------*/
56
ee1004_get_current_page(void)57 static int ee1004_get_current_page(void)
58 {
59 int err;
60
61 err = i2c_smbus_read_byte(ee1004_set_page[0]);
62 if (err == -ENXIO) {
63 /* Nack means page 1 is selected */
64 return 1;
65 }
66 if (err < 0) {
67 /* Anything else is a real error, bail out */
68 return err;
69 }
70
71 /* Ack means page 0 is selected, returned value meaningless */
72 return 0;
73 }
74
ee1004_set_current_page(struct device * dev,int page)75 static int ee1004_set_current_page(struct device *dev, int page)
76 {
77 int ret;
78
79 if (page == ee1004_current_page)
80 return 0;
81
82 /* Data is ignored */
83 ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
84 /*
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.
87 */
88 if (ret == -ENXIO && ee1004_get_current_page() == page)
89 ret = 0;
90 if (ret < 0) {
91 dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
92 return ret;
93 }
94
95 dev_dbg(dev, "Selected page %d\n", page);
96 ee1004_current_page = page;
97
98 return 0;
99 }
100
ee1004_eeprom_read(struct i2c_client * client,char * buf,unsigned int offset,size_t count)101 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
102 unsigned int offset, size_t count)
103 {
104 int status, page;
105
106 page = offset >> EE1004_PAGE_SHIFT;
107 offset &= (1 << EE1004_PAGE_SHIFT) - 1;
108
109 status = ee1004_set_current_page(&client->dev, page);
110 if (status)
111 return status;
112
113 /* Can't cross page boundaries */
114 if (offset + count > EE1004_PAGE_SIZE)
115 count = EE1004_PAGE_SIZE - offset;
116
117 if (count > I2C_SMBUS_BLOCK_MAX)
118 count = I2C_SMBUS_BLOCK_MAX;
119
120 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
121 }
122
eeprom_read(struct file * filp,struct kobject * kobj,struct bin_attribute * bin_attr,char * buf,loff_t off,size_t count)123 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
124 struct bin_attribute *bin_attr,
125 char *buf, loff_t off, size_t count)
126 {
127 struct i2c_client *client = kobj_to_i2c_client(kobj);
128 size_t requested = count;
129 int ret = 0;
130
131 /*
132 * Read data from chip, protecting against concurrent access to
133 * other EE1004 SPD EEPROMs on the same adapter.
134 */
135 mutex_lock(&ee1004_bus_lock);
136
137 while (count) {
138 ret = ee1004_eeprom_read(client, buf, off, count);
139 if (ret < 0)
140 goto out;
141
142 buf += ret;
143 off += ret;
144 count -= ret;
145 }
146 out:
147 mutex_unlock(&ee1004_bus_lock);
148
149 return ret < 0 ? ret : requested;
150 }
151
152 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
153
154 static struct bin_attribute *ee1004_attrs[] = {
155 &bin_attr_eeprom,
156 NULL
157 };
158
159 BIN_ATTRIBUTE_GROUPS(ee1004);
160
ee1004_cleanup(int idx)161 static void ee1004_cleanup(int idx)
162 {
163 if (--ee1004_dev_count == 0)
164 while (--idx >= 0) {
165 i2c_unregister_device(ee1004_set_page[idx]);
166 ee1004_set_page[idx] = NULL;
167 }
168 }
169
ee1004_probe(struct i2c_client * client)170 static int ee1004_probe(struct i2c_client *client)
171 {
172 int err, cnr = 0;
173
174 /* Make sure we can operate on this adapter */
175 if (!i2c_check_functionality(client->adapter,
176 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
177 !i2c_check_functionality(client->adapter,
178 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
179 return -EPFNOSUPPORT;
180
181 /* Use 2 dummy devices for page select command */
182 mutex_lock(&ee1004_bus_lock);
183 if (++ee1004_dev_count == 1) {
184 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
185 struct i2c_client *cl;
186
187 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
188 if (IS_ERR(cl)) {
189 err = PTR_ERR(cl);
190 goto err_clients;
191 }
192 ee1004_set_page[cnr] = cl;
193 }
194
195 /* Remember current page to avoid unneeded page select */
196 err = ee1004_get_current_page();
197 if (err < 0)
198 goto err_clients;
199 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
200 ee1004_current_page = err;
201 } else if (client->adapter != ee1004_set_page[0]->adapter) {
202 dev_err(&client->dev,
203 "Driver only supports devices on a single I2C bus\n");
204 err = -EOPNOTSUPP;
205 goto err_clients;
206 }
207 mutex_unlock(&ee1004_bus_lock);
208
209 dev_info(&client->dev,
210 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
211 EE1004_EEPROM_SIZE);
212
213 return 0;
214
215 err_clients:
216 ee1004_cleanup(cnr);
217 mutex_unlock(&ee1004_bus_lock);
218
219 return err;
220 }
221
ee1004_remove(struct i2c_client * client)222 static void ee1004_remove(struct i2c_client *client)
223 {
224 /* Remove page select clients if this is the last device */
225 mutex_lock(&ee1004_bus_lock);
226 ee1004_cleanup(EE1004_NUM_PAGES);
227 mutex_unlock(&ee1004_bus_lock);
228 }
229
230 /*-------------------------------------------------------------------------*/
231
232 static struct i2c_driver ee1004_driver = {
233 .driver = {
234 .name = "ee1004",
235 .dev_groups = ee1004_groups,
236 },
237 .probe = ee1004_probe,
238 .remove = ee1004_remove,
239 .id_table = ee1004_ids,
240 };
241 module_i2c_driver(ee1004_driver);
242
243 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
244 MODULE_AUTHOR("Jean Delvare");
245 MODULE_LICENSE("GPL");
246
