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_NUM_PAGES 2 36 #define EE1004_PAGE_SIZE 256 37 #define EE1004_PAGE_SHIFT 8 38 #define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES) 39 40 /* 41 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held 42 * from page selection to end of read. 43 */ 44 static DEFINE_MUTEX(ee1004_bus_lock); 45 static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES]; 46 static unsigned int ee1004_dev_count; 47 static int ee1004_current_page; 48 49 static const struct i2c_device_id ee1004_ids[] = { 50 { "ee1004", 0 }, 51 { } 52 }; 53 MODULE_DEVICE_TABLE(i2c, ee1004_ids); 54 55 /*-------------------------------------------------------------------------*/ 56 57 static int ee1004_get_current_page(void) 58 { 59 int err; 60 61 err = i2c_smbus_read_byte(ee1004_set_page[0]); 62 if (err == -ENXIO) { 63 /* Nack means page 1 is selected */ 64 return 1; 65 } 66 if (err < 0) { 67 /* Anything else is a real error, bail out */ 68 return err; 69 } 70 71 /* Ack means page 0 is selected, returned value meaningless */ 72 return 0; 73 } 74 75 static int ee1004_set_current_page(struct device *dev, int page) 76 { 77 int ret; 78 79 if (page == ee1004_current_page) 80 return 0; 81 82 /* Data is ignored */ 83 ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00); 84 /* 85 * Don't give up just yet. Some memory modules will select the page 86 * but not ack the command. Check which page is selected now. 87 */ 88 if (ret == -ENXIO && ee1004_get_current_page() == page) 89 ret = 0; 90 if (ret < 0) { 91 dev_err(dev, "Failed to select page %d (%d)\n", page, ret); 92 return ret; 93 } 94 95 dev_dbg(dev, "Selected page %d\n", page); 96 ee1004_current_page = page; 97 98 return 0; 99 } 100 101 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, 102 unsigned int offset, size_t count) 103 { 104 int status, page; 105 106 page = offset >> EE1004_PAGE_SHIFT; 107 offset &= (1 << EE1004_PAGE_SHIFT) - 1; 108 109 status = ee1004_set_current_page(&client->dev, page); 110 if (status) 111 return status; 112 113 /* Can't cross page boundaries */ 114 if (offset + count > EE1004_PAGE_SIZE) 115 count = EE1004_PAGE_SIZE - offset; 116 117 if (count > I2C_SMBUS_BLOCK_MAX) 118 count = I2C_SMBUS_BLOCK_MAX; 119 120 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf); 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 void ee1004_cleanup(int idx) 162 { 163 if (--ee1004_dev_count == 0) 164 while (--idx >= 0) { 165 i2c_unregister_device(ee1004_set_page[idx]); 166 ee1004_set_page[idx] = NULL; 167 } 168 } 169 170 static int ee1004_probe(struct i2c_client *client) 171 { 172 int err, cnr = 0; 173 174 /* Make sure we can operate on this adapter */ 175 if (!i2c_check_functionality(client->adapter, 176 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 177 !i2c_check_functionality(client->adapter, 178 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 179 return -EPFNOSUPPORT; 180 181 /* Use 2 dummy devices for page select command */ 182 mutex_lock(&ee1004_bus_lock); 183 if (++ee1004_dev_count == 1) { 184 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) { 185 struct i2c_client *cl; 186 187 cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr); 188 if (IS_ERR(cl)) { 189 err = PTR_ERR(cl); 190 goto err_clients; 191 } 192 ee1004_set_page[cnr] = cl; 193 } 194 195 /* Remember current page to avoid unneeded page select */ 196 err = ee1004_get_current_page(); 197 if (err < 0) 198 goto err_clients; 199 dev_dbg(&client->dev, "Currently selected page: %d\n", err); 200 ee1004_current_page = err; 201 } else if (client->adapter != ee1004_set_page[0]->adapter) { 202 dev_err(&client->dev, 203 "Driver only supports devices on a single I2C bus\n"); 204 err = -EOPNOTSUPP; 205 goto err_clients; 206 } 207 mutex_unlock(&ee1004_bus_lock); 208 209 dev_info(&client->dev, 210 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 211 EE1004_EEPROM_SIZE); 212 213 return 0; 214 215 err_clients: 216 ee1004_cleanup(cnr); 217 mutex_unlock(&ee1004_bus_lock); 218 219 return err; 220 } 221 222 static void ee1004_remove(struct i2c_client *client) 223 { 224 /* Remove page select clients if this is the last device */ 225 mutex_lock(&ee1004_bus_lock); 226 ee1004_cleanup(EE1004_NUM_PAGES); 227 mutex_unlock(&ee1004_bus_lock); 228 } 229 230 /*-------------------------------------------------------------------------*/ 231 232 static struct i2c_driver ee1004_driver = { 233 .driver = { 234 .name = "ee1004", 235 .dev_groups = ee1004_groups, 236 }, 237 .probe = ee1004_probe, 238 .remove = ee1004_remove, 239 .id_table = ee1004_ids, 240 }; 241 module_i2c_driver(ee1004_driver); 242 243 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 244 MODULE_AUTHOR("Jean Delvare"); 245 MODULE_LICENSE("GPL"); 246