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 int ee1004_set_current_page(struct device *dev, int page) 75 { 76 int ret; 77 78 if (page == ee1004_current_page) 79 return 0; 80 81 /* Data is ignored */ 82 ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00); 83 /* 84 * Don't give up just yet. Some memory modules will select the page 85 * but not ack the command. Check which page is selected now. 86 */ 87 if (ret == -ENXIO && ee1004_get_current_page() == page) 88 ret = 0; 89 if (ret < 0) { 90 dev_err(dev, "Failed to select page %d (%d)\n", page, ret); 91 return ret; 92 } 93 94 dev_dbg(dev, "Selected page %d\n", page); 95 ee1004_current_page = page; 96 97 return 0; 98 } 99 100 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, 101 unsigned int offset, size_t count) 102 { 103 int status; 104 105 /* Can't cross page boundaries */ 106 if (offset + count > EE1004_PAGE_SIZE) 107 count = EE1004_PAGE_SIZE - offset; 108 109 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, 110 count, buf); 111 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); 112 113 return status; 114 } 115 116 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, 117 struct bin_attribute *bin_attr, 118 char *buf, loff_t off, size_t count) 119 { 120 struct i2c_client *client = kobj_to_i2c_client(kobj); 121 size_t requested = count; 122 int page; 123 124 page = off >> EE1004_PAGE_SHIFT; 125 if (unlikely(page > 1)) 126 return 0; 127 off &= (1 << EE1004_PAGE_SHIFT) - 1; 128 129 /* 130 * Read data from chip, protecting against concurrent access to 131 * other EE1004 SPD EEPROMs on the same adapter. 132 */ 133 mutex_lock(&ee1004_bus_lock); 134 135 while (count) { 136 int status; 137 138 /* Select page */ 139 status = ee1004_set_current_page(dev, page); 140 if (status) { 141 mutex_unlock(&ee1004_bus_lock); 142 return status; 143 } 144 145 status = ee1004_eeprom_read(client, buf, off, count); 146 if (status < 0) { 147 mutex_unlock(&ee1004_bus_lock); 148 return status; 149 } 150 buf += status; 151 off += status; 152 count -= status; 153 154 if (off == EE1004_PAGE_SIZE) { 155 page++; 156 off = 0; 157 } 158 } 159 160 mutex_unlock(&ee1004_bus_lock); 161 162 return requested; 163 } 164 165 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 166 167 static struct bin_attribute *ee1004_attrs[] = { 168 &bin_attr_eeprom, 169 NULL 170 }; 171 172 BIN_ATTRIBUTE_GROUPS(ee1004); 173 174 static int ee1004_probe(struct i2c_client *client) 175 { 176 int err, cnr = 0; 177 178 /* Make sure we can operate on this adapter */ 179 if (!i2c_check_functionality(client->adapter, 180 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 181 !i2c_check_functionality(client->adapter, 182 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 183 return -EPFNOSUPPORT; 184 185 /* Use 2 dummy devices for page select command */ 186 mutex_lock(&ee1004_bus_lock); 187 if (++ee1004_dev_count == 1) { 188 for (cnr = 0; cnr < 2; cnr++) { 189 struct i2c_client *cl; 190 191 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr); 192 if (IS_ERR(cl)) { 193 err = PTR_ERR(cl); 194 goto err_clients; 195 } 196 ee1004_set_page[cnr] = cl; 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 dev_dbg(&client->dev, "Currently selected page: %d\n", err); 204 ee1004_current_page = err; 205 } else if (client->adapter != ee1004_set_page[0]->adapter) { 206 dev_err(&client->dev, 207 "Driver only supports devices on a single I2C bus\n"); 208 err = -EOPNOTSUPP; 209 goto err_clients; 210 } 211 mutex_unlock(&ee1004_bus_lock); 212 213 dev_info(&client->dev, 214 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 215 EE1004_EEPROM_SIZE); 216 217 return 0; 218 219 err_clients: 220 if (--ee1004_dev_count == 0) { 221 for (cnr--; cnr >= 0; cnr--) { 222 i2c_unregister_device(ee1004_set_page[cnr]); 223 ee1004_set_page[cnr] = NULL; 224 } 225 } 226 mutex_unlock(&ee1004_bus_lock); 227 228 return err; 229 } 230 231 static int ee1004_remove(struct i2c_client *client) 232 { 233 int i; 234 235 /* Remove page select clients if this is the last device */ 236 mutex_lock(&ee1004_bus_lock); 237 if (--ee1004_dev_count == 0) { 238 for (i = 0; i < 2; i++) { 239 i2c_unregister_device(ee1004_set_page[i]); 240 ee1004_set_page[i] = NULL; 241 } 242 } 243 mutex_unlock(&ee1004_bus_lock); 244 245 return 0; 246 } 247 248 /*-------------------------------------------------------------------------*/ 249 250 static struct i2c_driver ee1004_driver = { 251 .driver = { 252 .name = "ee1004", 253 .dev_groups = ee1004_groups, 254 }, 255 .probe_new = ee1004_probe, 256 .remove = ee1004_remove, 257 .id_table = ee1004_ids, 258 }; 259 module_i2c_driver(ee1004_driver); 260 261 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 262 MODULE_AUTHOR("Jean Delvare"); 263 MODULE_LICENSE("GPL"); 264