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/err.h> 13 #include <linux/i2c.h> 14 #include <linux/init.h> 15 #include <linux/kernel.h> 16 #include <linux/list.h> 17 #include <linux/mod_devicetable.h> 18 #include <linux/module.h> 19 #include <linux/mutex.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_ADDR_SET_PAGE0 0x36 37 #define EE1004_ADDR_SET_PAGE1 0x37 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 struct ee1004_bus { 44 struct kref kref; 45 struct list_head list; 46 struct mutex lock; 47 struct i2c_adapter *adapter; 48 struct i2c_client *set_page_clients[EE1004_NUM_PAGES]; 49 int page; 50 }; 51 52 static LIST_HEAD(ee1004_busses); 53 static DEFINE_MUTEX(ee1004_busses_lock); 54 55 static const struct i2c_device_id ee1004_ids[] = { 56 { "ee1004", 0 }, 57 { } 58 }; 59 MODULE_DEVICE_TABLE(i2c, ee1004_ids); 60 61 static const struct of_device_id ee1004_of_match[] = { 62 { .compatible = "atmel,at30tse004a" }, 63 {} 64 }; 65 MODULE_DEVICE_TABLE(of, ee1004_of_match); 66 67 /*-------------------------------------------------------------------------*/ 68 69 static int ee1004_get_current_page(struct ee1004_bus *bus) 70 { 71 int err; 72 73 err = i2c_smbus_read_byte(bus->set_page_clients[0]); 74 if (err == -ENXIO) { 75 /* Nack means page 1 is selected */ 76 return 1; 77 } 78 if (err < 0) { 79 /* Anything else is a real error, bail out */ 80 return err; 81 } 82 83 /* Ack means page 0 is selected, returned value meaningless */ 84 return 0; 85 } 86 87 static int ee1004_set_current_page(struct ee1004_bus *bus, int page) 88 { 89 int ret; 90 91 if (page == bus->page) 92 return 0; 93 94 /* Data is ignored */ 95 ret = i2c_smbus_write_byte(bus->set_page_clients[page], 0x00); 96 97 /* 98 * Don't give up just yet. Some memory modules will select the page 99 * but not ack the command. Check which page is selected now. 100 */ 101 if (ret == -ENXIO && ee1004_get_current_page(bus) == page) 102 ret = 0; 103 if (ret < 0) 104 return ret; 105 106 bus->page = page; 107 return 0; 108 } 109 110 static ssize_t ee1004_eeprom_read(struct i2c_client *client, struct ee1004_bus *bus, char *buf, 111 unsigned int offset, size_t count) 112 { 113 int status, page; 114 115 page = offset >> EE1004_PAGE_SHIFT; 116 offset &= (1 << EE1004_PAGE_SHIFT) - 1; 117 118 status = ee1004_set_current_page(bus, page); 119 if (status) { 120 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, status); 121 return status; 122 } 123 124 /* Can't cross page boundaries */ 125 if (offset + count > EE1004_PAGE_SIZE) 126 count = EE1004_PAGE_SIZE - offset; 127 128 if (count > I2C_SMBUS_BLOCK_MAX) 129 count = I2C_SMBUS_BLOCK_MAX; 130 131 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf); 132 } 133 134 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, 135 struct bin_attribute *bin_attr, 136 char *buf, loff_t off, size_t count) 137 { 138 struct i2c_client *client = kobj_to_i2c_client(kobj); 139 struct ee1004_bus *bus = i2c_get_clientdata(client); 140 size_t requested = count; 141 int ret = 0; 142 143 /* 144 * Read data from chip, protecting against concurrent access to 145 * other EE1004 SPD EEPROMs on the same adapter. 146 */ 147 mutex_lock(&bus->lock); 148 149 while (count) { 150 ret = ee1004_eeprom_read(client, bus, buf, off, count); 151 if (ret < 0) 152 goto out; 153 154 buf += ret; 155 off += ret; 156 count -= ret; 157 } 158 out: 159 mutex_unlock(&bus->lock); 160 161 return ret < 0 ? ret : requested; 162 } 163 164 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 165 166 static struct bin_attribute *ee1004_attrs[] = { 167 &bin_attr_eeprom, 168 NULL 169 }; 170 171 BIN_ATTRIBUTE_GROUPS(ee1004); 172 173 static void ee1004_bus_unregister(struct ee1004_bus *bus) 174 { 175 i2c_unregister_device(bus->set_page_clients[1]); 176 i2c_unregister_device(bus->set_page_clients[0]); 177 } 178 179 static void ee1004_bus_release(struct kref *kref) 180 { 181 struct ee1004_bus *bus = container_of(kref, struct ee1004_bus, kref); 182 183 ee1004_bus_unregister(bus); 184 185 mutex_lock(&ee1004_busses_lock); 186 list_del(&bus->list); 187 mutex_unlock(&ee1004_busses_lock); 188 189 kfree(bus); 190 } 191 192 static int ee1004_bus_initialize(struct ee1004_bus *bus, struct i2c_adapter *adapter) 193 { 194 bus->set_page_clients[0] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE0); 195 if (IS_ERR(bus->set_page_clients[0])) 196 return PTR_ERR(bus->set_page_clients[0]); 197 198 bus->set_page_clients[1] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE1); 199 if (IS_ERR(bus->set_page_clients[1])) { 200 i2c_unregister_device(bus->set_page_clients[0]); 201 return PTR_ERR(bus->set_page_clients[1]); 202 } 203 204 bus->page = ee1004_get_current_page(bus); 205 if (bus->page < 0) { 206 ee1004_bus_unregister(bus); 207 return bus->page; 208 } 209 210 kref_init(&bus->kref); 211 list_add(&bus->list, &ee1004_busses); 212 mutex_init(&bus->lock); 213 bus->adapter = adapter; 214 215 return 0; 216 } 217 218 static int ee1004_probe(struct i2c_client *client) 219 { 220 struct ee1004_bus *bus; 221 bool found = false; 222 int rc = 0; 223 224 /* Make sure we can operate on this adapter */ 225 if (!i2c_check_functionality(client->adapter, 226 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 227 !i2c_check_functionality(client->adapter, 228 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 229 return -EPFNOSUPPORT; 230 231 mutex_lock(&ee1004_busses_lock); 232 list_for_each_entry(bus, &ee1004_busses, list) { 233 if (bus->adapter == client->adapter) { 234 kref_get(&bus->kref); 235 found = true; 236 break; 237 } 238 } 239 240 if (!found) { 241 bus = kzalloc(sizeof(*bus), GFP_KERNEL); 242 if (!bus) { 243 rc = -ENOMEM; 244 goto unlock; 245 } 246 247 rc = ee1004_bus_initialize(bus, client->adapter); 248 if (rc) { 249 kfree(bus); 250 goto unlock; 251 } 252 } 253 254 i2c_set_clientdata(client, bus); 255 256 dev_info(&client->dev, 257 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 258 EE1004_EEPROM_SIZE); 259 260 unlock: 261 mutex_unlock(&ee1004_busses_lock); 262 return rc; 263 } 264 265 static void ee1004_remove(struct i2c_client *client) 266 { 267 struct ee1004_bus *bus = i2c_get_clientdata(client); 268 269 kref_put(&bus->kref, ee1004_bus_release); 270 } 271 272 /*-------------------------------------------------------------------------*/ 273 274 static struct i2c_driver ee1004_driver = { 275 .driver = { 276 .name = "ee1004", 277 .dev_groups = ee1004_groups, 278 .of_match_table = ee1004_of_match, 279 }, 280 .probe = ee1004_probe, 281 .remove = ee1004_remove, 282 .id_table = ee1004_ids, 283 }; 284 module_i2c_driver(ee1004_driver); 285 286 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 287 MODULE_AUTHOR("Jean Delvare"); 288 MODULE_LICENSE("GPL"); 289