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 eeprom_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 i2c_client *client = kobj_to_i2c_client(kobj); 97 size_t requested = count; 98 int page; 99 100 if (unlikely(!count)) 101 return count; 102 103 page = off >> EE1004_PAGE_SHIFT; 104 if (unlikely(page > 1)) 105 return 0; 106 off &= (1 << EE1004_PAGE_SHIFT) - 1; 107 108 /* 109 * Read data from chip, protecting against concurrent access to 110 * other EE1004 SPD EEPROMs on the same adapter. 111 */ 112 mutex_lock(&ee1004_bus_lock); 113 114 while (count) { 115 int status; 116 117 /* Select page */ 118 if (page != ee1004_current_page) { 119 /* Data is ignored */ 120 status = i2c_smbus_write_byte(ee1004_set_page[page], 121 0x00); 122 if (status == -ENXIO) { 123 /* 124 * Don't give up just yet. Some memory 125 * modules will select the page but not 126 * ack the command. Check which page is 127 * selected now. 128 */ 129 if (ee1004_get_current_page() == page) 130 status = 0; 131 } 132 if (status < 0) { 133 dev_err(dev, "Failed to select page %d (%d)\n", 134 page, status); 135 mutex_unlock(&ee1004_bus_lock); 136 return status; 137 } 138 dev_dbg(dev, "Selected page %d\n", page); 139 ee1004_current_page = page; 140 } 141 142 status = ee1004_eeprom_read(client, buf, off, count); 143 if (status < 0) { 144 mutex_unlock(&ee1004_bus_lock); 145 return status; 146 } 147 buf += status; 148 off += status; 149 count -= status; 150 151 if (off == EE1004_PAGE_SIZE) { 152 page++; 153 off = 0; 154 } 155 } 156 157 mutex_unlock(&ee1004_bus_lock); 158 159 return requested; 160 } 161 162 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 163 164 static struct bin_attribute *ee1004_attrs[] = { 165 &bin_attr_eeprom, 166 NULL 167 }; 168 169 BIN_ATTRIBUTE_GROUPS(ee1004); 170 171 static int ee1004_probe(struct i2c_client *client, 172 const struct i2c_device_id *id) 173 { 174 int err, cnr = 0; 175 const char *slow = NULL; 176 177 /* Make sure we can operate on this adapter */ 178 if (!i2c_check_functionality(client->adapter, 179 I2C_FUNC_SMBUS_READ_BYTE | 180 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) { 181 if (i2c_check_functionality(client->adapter, 182 I2C_FUNC_SMBUS_READ_BYTE | 183 I2C_FUNC_SMBUS_READ_WORD_DATA)) 184 slow = "word"; 185 else if (i2c_check_functionality(client->adapter, 186 I2C_FUNC_SMBUS_READ_BYTE | 187 I2C_FUNC_SMBUS_READ_BYTE_DATA)) 188 slow = "byte"; 189 else 190 return -EPFNOSUPPORT; 191 } 192 193 /* Use 2 dummy devices for page select command */ 194 mutex_lock(&ee1004_bus_lock); 195 if (++ee1004_dev_count == 1) { 196 for (cnr = 0; cnr < 2; cnr++) { 197 ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter, 198 EE1004_ADDR_SET_PAGE + cnr); 199 if (IS_ERR(ee1004_set_page[cnr])) { 200 dev_err(&client->dev, 201 "address 0x%02x unavailable\n", 202 EE1004_ADDR_SET_PAGE + cnr); 203 err = PTR_ERR(ee1004_set_page[cnr]); 204 goto err_clients; 205 } 206 } 207 } else if (i2c_adapter_id(client->adapter) != 208 i2c_adapter_id(ee1004_set_page[0]->adapter)) { 209 dev_err(&client->dev, 210 "Driver only supports devices on a single I2C bus\n"); 211 err = -EOPNOTSUPP; 212 goto err_clients; 213 } 214 215 /* Remember current page to avoid unneeded page select */ 216 err = ee1004_get_current_page(); 217 if (err < 0) 218 goto err_clients; 219 ee1004_current_page = err; 220 dev_dbg(&client->dev, "Currently selected page: %d\n", 221 ee1004_current_page); 222 mutex_unlock(&ee1004_bus_lock); 223 224 dev_info(&client->dev, 225 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 226 EE1004_EEPROM_SIZE); 227 if (slow) 228 dev_notice(&client->dev, 229 "Falling back to %s reads, performance will suffer\n", 230 slow); 231 232 return 0; 233 234 err_clients: 235 if (--ee1004_dev_count == 0) { 236 for (cnr--; cnr >= 0; cnr--) { 237 i2c_unregister_device(ee1004_set_page[cnr]); 238 ee1004_set_page[cnr] = NULL; 239 } 240 } 241 mutex_unlock(&ee1004_bus_lock); 242 243 return err; 244 } 245 246 static int ee1004_remove(struct i2c_client *client) 247 { 248 int i; 249 250 /* Remove page select clients if this is the last device */ 251 mutex_lock(&ee1004_bus_lock); 252 if (--ee1004_dev_count == 0) { 253 for (i = 0; i < 2; i++) { 254 i2c_unregister_device(ee1004_set_page[i]); 255 ee1004_set_page[i] = NULL; 256 } 257 } 258 mutex_unlock(&ee1004_bus_lock); 259 260 return 0; 261 } 262 263 /*-------------------------------------------------------------------------*/ 264 265 static struct i2c_driver ee1004_driver = { 266 .driver = { 267 .name = "ee1004", 268 .dev_groups = ee1004_groups, 269 }, 270 .probe = ee1004_probe, 271 .remove = ee1004_remove, 272 .id_table = ee1004_ids, 273 }; 274 module_i2c_driver(ee1004_driver); 275 276 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 277 MODULE_AUTHOR("Jean Delvare"); 278 MODULE_LICENSE("GPL"); 279