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 */ 47 static DEFINE_MUTEX(ee1004_bus_lock); 48 49 static 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 56 static const struct i2c_device_id ee1004_ids[] = { 57 { "ee1004" }, 58 { } 59 }; 60 MODULE_DEVICE_TABLE(i2c, ee1004_ids); 61 62 /*-------------------------------------------------------------------------*/ 63 64 static 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 82 static int ee1004_get_current_page(struct ee1004_bus_data *bd) 83 { 84 int err; 85 86 err = i2c_smbus_read_byte(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 } 99 100 static 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(bd->set_page[page], 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 } 126 127 static 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, offset, count, buf); 147 } 148 149 static 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, off, count); 169 if (ret < 0) { 170 mutex_unlock(&ee1004_bus_lock); 171 return ret; 172 } 173 174 buf += ret; 175 off += ret; 176 count -= ret; 177 } 178 179 mutex_unlock(&ee1004_bus_lock); 180 181 return 0; 182 } 183 184 static 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, data, 14, 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, data, 1, 2); 211 if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c) 212 return; 213 } 214 i2c_new_scanned_device(client->adapter, &info, addr_list, NULL); 215 } 216 217 static 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(bd->set_page[idx]); 222 memset(bd, 0, sizeof(struct ee1004_bus_data)); 223 } 224 } 225 226 static 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(&ee1004_bus_lock); 234 } 235 236 static 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(client->adapter); 242 if (!bd) 243 return dev_err_probe(&client->dev, -ENOSPC, "Only %d busses supported", 244 EE1004_MAX_BUSSES); 245 246 i2c_set_clientdata(client, 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(client->adapter, EE1004_ADDR_SET_PAGE + cnr); 254 if (IS_ERR(cl)) { 255 err = PTR_ERR(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; 272 273 err_out: 274 ee1004_cleanup(cnr, bd); 275 276 return err; 277 } 278 279 static int ee1004_probe(struct i2c_client *client) 280 { 281 struct nvmem_config config = { 282 .dev = &client->dev, 283 .name = dev_name(&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(client->adapter, 302 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 303 !i2c_check_functionality(client->adapter, 304 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 305 return -EPFNOSUPPORT; 306 307 mutex_lock(&ee1004_bus_lock); 308 309 err = ee1004_init_bus_data(client); 310 if (err < 0) { 311 mutex_unlock(&ee1004_bus_lock); 312 return err; 313 } 314 315 ee1004_probe_temp_sensor(client); 316 317 mutex_unlock(&ee1004_bus_lock); 318 319 err = devm_add_action_or_reset(&client->dev, ee1004_cleanup_bus_data, 320 i2c_get_clientdata(client)); 321 if (err < 0) 322 return err; 323 324 ndev = devm_nvmem_register(&client->dev, &config); 325 if (IS_ERR(ndev)) 326 return PTR_ERR(ndev); 327 328 dev_info(&client->dev, 329 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 330 EE1004_EEPROM_SIZE); 331 332 return 0; 333 } 334 335 /*-------------------------------------------------------------------------*/ 336 337 static struct i2c_driver ee1004_driver = { 338 .driver = { 339 .name = "ee1004", 340 }, 341 .probe = ee1004_probe, 342 .id_table = ee1004_ids, 343 }; 344 module_i2c_driver(ee1004_driver); 345 346 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 347 MODULE_AUTHOR("Jean Delvare"); 348 MODULE_LICENSE("GPL"); 349