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 /* Can't cross page boundaries */ 80 if (offset + count > EE1004_PAGE_SIZE) 81 count = EE1004_PAGE_SIZE - offset; 82 83 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, 84 count, buf); 85 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); 86 87 return status; 88 } 89 90 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, 91 struct bin_attribute *bin_attr, 92 char *buf, loff_t off, size_t count) 93 { 94 struct i2c_client *client = kobj_to_i2c_client(kobj); 95 size_t requested = count; 96 int page; 97 98 page = off >> EE1004_PAGE_SHIFT; 99 if (unlikely(page > 1)) 100 return 0; 101 off &= (1 << EE1004_PAGE_SHIFT) - 1; 102 103 /* 104 * Read data from chip, protecting against concurrent access to 105 * other EE1004 SPD EEPROMs on the same adapter. 106 */ 107 mutex_lock(&ee1004_bus_lock); 108 109 while (count) { 110 int status; 111 112 /* Select page */ 113 if (page != ee1004_current_page) { 114 /* Data is ignored */ 115 status = i2c_smbus_write_byte(ee1004_set_page[page], 116 0x00); 117 if (status == -ENXIO) { 118 /* 119 * Don't give up just yet. Some memory 120 * modules will select the page but not 121 * ack the command. Check which page is 122 * selected now. 123 */ 124 if (ee1004_get_current_page() == page) 125 status = 0; 126 } 127 if (status < 0) { 128 dev_err(dev, "Failed to select page %d (%d)\n", 129 page, status); 130 mutex_unlock(&ee1004_bus_lock); 131 return status; 132 } 133 dev_dbg(dev, "Selected page %d\n", page); 134 ee1004_current_page = page; 135 } 136 137 status = ee1004_eeprom_read(client, buf, off, count); 138 if (status < 0) { 139 mutex_unlock(&ee1004_bus_lock); 140 return status; 141 } 142 buf += status; 143 off += status; 144 count -= status; 145 146 if (off == EE1004_PAGE_SIZE) { 147 page++; 148 off = 0; 149 } 150 } 151 152 mutex_unlock(&ee1004_bus_lock); 153 154 return requested; 155 } 156 157 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 158 159 static struct bin_attribute *ee1004_attrs[] = { 160 &bin_attr_eeprom, 161 NULL 162 }; 163 164 BIN_ATTRIBUTE_GROUPS(ee1004); 165 166 static int ee1004_probe(struct i2c_client *client, 167 const struct i2c_device_id *id) 168 { 169 int err, cnr = 0; 170 171 /* Make sure we can operate on this adapter */ 172 if (!i2c_check_functionality(client->adapter, 173 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 174 !i2c_check_functionality(client->adapter, 175 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 176 return -EPFNOSUPPORT; 177 178 /* Use 2 dummy devices for page select command */ 179 mutex_lock(&ee1004_bus_lock); 180 if (++ee1004_dev_count == 1) { 181 for (cnr = 0; cnr < 2; cnr++) { 182 ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter, 183 EE1004_ADDR_SET_PAGE + cnr); 184 if (IS_ERR(ee1004_set_page[cnr])) { 185 dev_err(&client->dev, 186 "address 0x%02x unavailable\n", 187 EE1004_ADDR_SET_PAGE + cnr); 188 err = PTR_ERR(ee1004_set_page[cnr]); 189 goto err_clients; 190 } 191 } 192 } else if (client->adapter != ee1004_set_page[0]->adapter) { 193 dev_err(&client->dev, 194 "Driver only supports devices on a single I2C bus\n"); 195 err = -EOPNOTSUPP; 196 goto err_clients; 197 } 198 199 /* Remember current page to avoid unneeded page select */ 200 err = ee1004_get_current_page(); 201 if (err < 0) 202 goto err_clients; 203 ee1004_current_page = err; 204 dev_dbg(&client->dev, "Currently selected page: %d\n", 205 ee1004_current_page); 206 mutex_unlock(&ee1004_bus_lock); 207 208 dev_info(&client->dev, 209 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 210 EE1004_EEPROM_SIZE); 211 212 return 0; 213 214 err_clients: 215 if (--ee1004_dev_count == 0) { 216 for (cnr--; cnr >= 0; cnr--) { 217 i2c_unregister_device(ee1004_set_page[cnr]); 218 ee1004_set_page[cnr] = NULL; 219 } 220 } 221 mutex_unlock(&ee1004_bus_lock); 222 223 return err; 224 } 225 226 static int ee1004_remove(struct i2c_client *client) 227 { 228 int i; 229 230 /* Remove page select clients if this is the last device */ 231 mutex_lock(&ee1004_bus_lock); 232 if (--ee1004_dev_count == 0) { 233 for (i = 0; i < 2; i++) { 234 i2c_unregister_device(ee1004_set_page[i]); 235 ee1004_set_page[i] = NULL; 236 } 237 } 238 mutex_unlock(&ee1004_bus_lock); 239 240 return 0; 241 } 242 243 /*-------------------------------------------------------------------------*/ 244 245 static struct i2c_driver ee1004_driver = { 246 .driver = { 247 .name = "ee1004", 248 .dev_groups = ee1004_groups, 249 }, 250 .probe = ee1004_probe, 251 .remove = ee1004_remove, 252 .id_table = ee1004_ids, 253 }; 254 module_i2c_driver(ee1004_driver); 255 256 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 257 MODULE_AUTHOR("Jean Delvare"); 258 MODULE_LICENSE("GPL"); 259