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_EEPROM_SIZE 512 36 #define EE1004_PAGE_SIZE 256 37 #define EE1004_PAGE_SHIFT 8 38 39 /* 40 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held 41 * from page selection to end of read. 42 */ 43 static DEFINE_MUTEX(ee1004_bus_lock); 44 static struct i2c_client *ee1004_set_page[2]; 45 static unsigned int ee1004_dev_count; 46 static int ee1004_current_page; 47 48 static const struct i2c_device_id ee1004_ids[] = { 49 { "ee1004", 0 }, 50 { } 51 }; 52 MODULE_DEVICE_TABLE(i2c, ee1004_ids); 53 54 /*-------------------------------------------------------------------------*/ 55 56 static int ee1004_get_current_page(void) 57 { 58 int err; 59 60 err = i2c_smbus_read_byte(ee1004_set_page[0]); 61 if (err == -ENXIO) { 62 /* Nack means page 1 is selected */ 63 return 1; 64 } 65 if (err < 0) { 66 /* Anything else is a real error, bail out */ 67 return err; 68 } 69 70 /* Ack means page 0 is selected, returned value meaningless */ 71 return 0; 72 } 73 74 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, 75 unsigned int offset, size_t count) 76 { 77 int status; 78 79 if (count > I2C_SMBUS_BLOCK_MAX) 80 count = I2C_SMBUS_BLOCK_MAX; 81 /* Can't cross page boundaries */ 82 if (unlikely(offset + count > EE1004_PAGE_SIZE)) 83 count = EE1004_PAGE_SIZE - offset; 84 85 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, 86 count, buf); 87 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); 88 89 return status; 90 } 91 92 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj, 93 struct bin_attribute *bin_attr, 94 char *buf, loff_t off, size_t count) 95 { 96 struct device *dev = kobj_to_dev(kobj); 97 struct i2c_client *client = to_i2c_client(dev); 98 size_t requested = count; 99 int page; 100 101 if (unlikely(!count)) 102 return count; 103 104 page = off >> EE1004_PAGE_SHIFT; 105 if (unlikely(page > 1)) 106 return 0; 107 off &= (1 << EE1004_PAGE_SHIFT) - 1; 108 109 /* 110 * Read data from chip, protecting against concurrent access to 111 * other EE1004 SPD EEPROMs on the same adapter. 112 */ 113 mutex_lock(&ee1004_bus_lock); 114 115 while (count) { 116 int status; 117 118 /* Select page */ 119 if (page != ee1004_current_page) { 120 /* Data is ignored */ 121 status = i2c_smbus_write_byte(ee1004_set_page[page], 122 0x00); 123 if (status == -ENXIO) { 124 /* 125 * Don't give up just yet. Some memory 126 * modules will select the page but not 127 * ack the command. Check which page is 128 * selected now. 129 */ 130 if (ee1004_get_current_page() == page) 131 status = 0; 132 } 133 if (status < 0) { 134 dev_err(dev, "Failed to select page %d (%d)\n", 135 page, status); 136 mutex_unlock(&ee1004_bus_lock); 137 return status; 138 } 139 dev_dbg(dev, "Selected page %d\n", page); 140 ee1004_current_page = page; 141 } 142 143 status = ee1004_eeprom_read(client, buf, off, count); 144 if (status < 0) { 145 mutex_unlock(&ee1004_bus_lock); 146 return status; 147 } 148 buf += status; 149 off += status; 150 count -= status; 151 152 if (off == EE1004_PAGE_SIZE) { 153 page++; 154 off = 0; 155 } 156 } 157 158 mutex_unlock(&ee1004_bus_lock); 159 160 return requested; 161 } 162 163 static const struct bin_attribute eeprom_attr = { 164 .attr = { 165 .name = "eeprom", 166 .mode = 0444, 167 }, 168 .size = EE1004_EEPROM_SIZE, 169 .read = ee1004_read, 170 }; 171 172 static int ee1004_probe(struct i2c_client *client, 173 const struct i2c_device_id *id) 174 { 175 int err, cnr = 0; 176 const char *slow = NULL; 177 178 /* Make sure we can operate on this adapter */ 179 if (!i2c_check_functionality(client->adapter, 180 I2C_FUNC_SMBUS_READ_BYTE | 181 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) { 182 if (i2c_check_functionality(client->adapter, 183 I2C_FUNC_SMBUS_READ_BYTE | 184 I2C_FUNC_SMBUS_READ_WORD_DATA)) 185 slow = "word"; 186 else if (i2c_check_functionality(client->adapter, 187 I2C_FUNC_SMBUS_READ_BYTE | 188 I2C_FUNC_SMBUS_READ_BYTE_DATA)) 189 slow = "byte"; 190 else 191 return -EPFNOSUPPORT; 192 } 193 194 /* Use 2 dummy devices for page select command */ 195 mutex_lock(&ee1004_bus_lock); 196 if (++ee1004_dev_count == 1) { 197 for (cnr = 0; cnr < 2; cnr++) { 198 ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter, 199 EE1004_ADDR_SET_PAGE + cnr); 200 if (IS_ERR(ee1004_set_page[cnr])) { 201 dev_err(&client->dev, 202 "address 0x%02x unavailable\n", 203 EE1004_ADDR_SET_PAGE + cnr); 204 err = PTR_ERR(ee1004_set_page[cnr]); 205 goto err_clients; 206 } 207 } 208 } else if (i2c_adapter_id(client->adapter) != 209 i2c_adapter_id(ee1004_set_page[0]->adapter)) { 210 dev_err(&client->dev, 211 "Driver only supports devices on a single I2C bus\n"); 212 err = -EOPNOTSUPP; 213 goto err_clients; 214 } 215 216 /* Remember current page to avoid unneeded page select */ 217 err = ee1004_get_current_page(); 218 if (err < 0) 219 goto err_clients; 220 ee1004_current_page = err; 221 dev_dbg(&client->dev, "Currently selected page: %d\n", 222 ee1004_current_page); 223 mutex_unlock(&ee1004_bus_lock); 224 225 /* Create the sysfs eeprom file */ 226 err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr); 227 if (err) 228 goto err_clients_lock; 229 230 dev_info(&client->dev, 231 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 232 EE1004_EEPROM_SIZE); 233 if (slow) 234 dev_notice(&client->dev, 235 "Falling back to %s reads, performance will suffer\n", 236 slow); 237 238 return 0; 239 240 err_clients_lock: 241 mutex_lock(&ee1004_bus_lock); 242 err_clients: 243 if (--ee1004_dev_count == 0) { 244 for (cnr--; cnr >= 0; cnr--) { 245 i2c_unregister_device(ee1004_set_page[cnr]); 246 ee1004_set_page[cnr] = NULL; 247 } 248 } 249 mutex_unlock(&ee1004_bus_lock); 250 251 return err; 252 } 253 254 static int ee1004_remove(struct i2c_client *client) 255 { 256 int i; 257 258 sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr); 259 260 /* Remove page select clients if this is the last device */ 261 mutex_lock(&ee1004_bus_lock); 262 if (--ee1004_dev_count == 0) { 263 for (i = 0; i < 2; i++) { 264 i2c_unregister_device(ee1004_set_page[i]); 265 ee1004_set_page[i] = NULL; 266 } 267 } 268 mutex_unlock(&ee1004_bus_lock); 269 270 return 0; 271 } 272 273 /*-------------------------------------------------------------------------*/ 274 275 static struct i2c_driver ee1004_driver = { 276 .driver = { 277 .name = "ee1004", 278 }, 279 .probe = ee1004_probe, 280 .remove = ee1004_remove, 281 .id_table = ee1004_ids, 282 }; 283 module_i2c_driver(ee1004_driver); 284 285 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 286 MODULE_AUTHOR("Jean Delvare"); 287 MODULE_LICENSE("GPL"); 288