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, page; 104 105 page = offset >> EE1004_PAGE_SHIFT; 106 offset &= (1 << EE1004_PAGE_SHIFT) - 1; 107 108 status = ee1004_set_current_page(&client->dev, page); 109 if (status) 110 return status; 111 112 /* Can't cross page boundaries */ 113 if (offset + count > EE1004_PAGE_SIZE) 114 count = EE1004_PAGE_SIZE - offset; 115 116 status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset, 117 count, buf); 118 dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status); 119 120 return status; 121 } 122 123 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, 124 struct bin_attribute *bin_attr, 125 char *buf, loff_t off, size_t count) 126 { 127 struct i2c_client *client = kobj_to_i2c_client(kobj); 128 size_t requested = count; 129 int ret = 0; 130 131 /* 132 * Read data from chip, protecting against concurrent access to 133 * other EE1004 SPD EEPROMs on the same adapter. 134 */ 135 mutex_lock(&ee1004_bus_lock); 136 137 while (count) { 138 ret = ee1004_eeprom_read(client, buf, off, count); 139 if (ret < 0) 140 goto out; 141 142 buf += ret; 143 off += ret; 144 count -= ret; 145 } 146 out: 147 mutex_unlock(&ee1004_bus_lock); 148 149 return ret < 0 ? ret : requested; 150 } 151 152 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 153 154 static struct bin_attribute *ee1004_attrs[] = { 155 &bin_attr_eeprom, 156 NULL 157 }; 158 159 BIN_ATTRIBUTE_GROUPS(ee1004); 160 161 static int ee1004_probe(struct i2c_client *client) 162 { 163 int err, cnr = 0; 164 165 /* Make sure we can operate on this adapter */ 166 if (!i2c_check_functionality(client->adapter, 167 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 168 !i2c_check_functionality(client->adapter, 169 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 170 return -EPFNOSUPPORT; 171 172 /* Use 2 dummy devices for page select command */ 173 mutex_lock(&ee1004_bus_lock); 174 if (++ee1004_dev_count == 1) { 175 for (cnr = 0; cnr < 2; cnr++) { 176 struct i2c_client *cl; 177 178 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr); 179 if (IS_ERR(cl)) { 180 err = PTR_ERR(cl); 181 goto err_clients; 182 } 183 ee1004_set_page[cnr] = cl; 184 } 185 186 /* Remember current page to avoid unneeded page select */ 187 err = ee1004_get_current_page(); 188 if (err < 0) 189 goto err_clients; 190 dev_dbg(&client->dev, "Currently selected page: %d\n", err); 191 ee1004_current_page = err; 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 mutex_unlock(&ee1004_bus_lock); 199 200 dev_info(&client->dev, 201 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 202 EE1004_EEPROM_SIZE); 203 204 return 0; 205 206 err_clients: 207 if (--ee1004_dev_count == 0) { 208 for (cnr--; cnr >= 0; cnr--) { 209 i2c_unregister_device(ee1004_set_page[cnr]); 210 ee1004_set_page[cnr] = NULL; 211 } 212 } 213 mutex_unlock(&ee1004_bus_lock); 214 215 return err; 216 } 217 218 static int ee1004_remove(struct i2c_client *client) 219 { 220 int i; 221 222 /* Remove page select clients if this is the last device */ 223 mutex_lock(&ee1004_bus_lock); 224 if (--ee1004_dev_count == 0) { 225 for (i = 0; i < 2; i++) { 226 i2c_unregister_device(ee1004_set_page[i]); 227 ee1004_set_page[i] = NULL; 228 } 229 } 230 mutex_unlock(&ee1004_bus_lock); 231 232 return 0; 233 } 234 235 /*-------------------------------------------------------------------------*/ 236 237 static struct i2c_driver ee1004_driver = { 238 .driver = { 239 .name = "ee1004", 240 .dev_groups = ee1004_groups, 241 }, 242 .probe_new = ee1004_probe, 243 .remove = ee1004_remove, 244 .id_table = ee1004_ids, 245 }; 246 module_i2c_driver(ee1004_driver); 247 248 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 249 MODULE_AUTHOR("Jean Delvare"); 250 MODULE_LICENSE("GPL"); 251