drivers/misc/eeprom/ee1004.c

   1 /*
   2  * ee1004 - driver for DDR4 SPD EEPROMs
   3  *
   4  * Copyright (C) 2017 Jean Delvare
   5  *
   6  * Based on the at24 driver:
   7  * Copyright (C) 2005-2007 David Brownell
   8  * Copyright (C) 2008 Wolfram Sang, Pengutronix
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License as published by
  12  * the Free Software Foundation; either version 2 of the License, or
  13  * (at your option) any later version.
  14  */
  15
  16 #include <linux/i2c.h>
  17 #include <linux/init.h>
  18 #include <linux/kernel.h>
  19 #include <linux/mod_devicetable.h>
  20 #include <linux/module.h>
  21 #include <linux/mutex.h>
  22
  23 /*
  24  * DDR4 memory modules use special EEPROMs following the Jedec EE1004
  25  * specification. These are 512-byte EEPROMs using a single I2C address
  26  * in the 0x50-0x57 range for data. One of two 256-byte page is selected
  27  * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
  28  *
  29  * Therefore we need to request these 2 additional addresses, and serialize
  30  * access to all such EEPROMs with a single mutex.
  31  *
  32  * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
  33  * We use SMBus access even if I2C is available, these EEPROMs are small
  34  * enough, and reading from them infrequent enough, that we favor simplicity
  35  * over performance.
  36  */
  37
  38 #define EE1004_ADDR_SET_PAGE            0x36
  39 #define EE1004_EEPROM_SIZE              512
  40 #define EE1004_PAGE_SIZE                256
  41 #define EE1004_PAGE_SHIFT               8
  42
  43 /*
  44  * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
  45  * from page selection to end of read.
  46  */
  47 static DEFINE_MUTEX(ee1004_bus_lock);
  48 static struct i2c_client *ee1004_set_page[2];
  49 static unsigned int ee1004_dev_count;
  50 static int ee1004_current_page;
  51
  52 static const struct i2c_device_id ee1004_ids[] = {
  53         { "ee1004", 0 },
  54         { }
  55 };
  56 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
  57
  58 /*-------------------------------------------------------------------------*/
  59
  60 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
  61                                   unsigned int offset, size_t count)
  62 {
  63         int status;
  64
  65         if (count > I2C_SMBUS_BLOCK_MAX)
  66                 count = I2C_SMBUS_BLOCK_MAX;
  67         /* Can't cross page boundaries */
  68         if (unlikely(offset + count > EE1004_PAGE_SIZE))
  69                 count = EE1004_PAGE_SIZE - offset;
  70
  71         status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
  72                                                            count, buf);
  73         dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
  74
  75         return status;
  76 }
  77
  78 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
  79                            struct bin_attribute *bin_attr,
  80                            char *buf, loff_t off, size_t count)
  81 {
  82         struct device *dev = kobj_to_dev(kobj);
  83         struct i2c_client *client = to_i2c_client(dev);
  84         size_t requested = count;
  85         int page;
  86
  87         if (unlikely(!count))
  88                 return count;
  89
  90         page = off >> EE1004_PAGE_SHIFT;
  91         if (unlikely(page > 1))
  92                 return 0;
  93         off &= (1 << EE1004_PAGE_SHIFT) - 1;
  94
  95         /*
  96          * Read data from chip, protecting against concurrent access to
  97          * other EE1004 SPD EEPROMs on the same adapter.
  98          */
  99         mutex_lock(&ee1004_bus_lock);
 100
 101         while (count) {
 102                 int status;
 103
 104                 /* Select page */
 105                 if (page != ee1004_current_page) {
 106                         /* Data is ignored */
 107                         status = i2c_smbus_write_byte(ee1004_set_page[page],
 108                                                       0x00);
 109                         if (status < 0) {
 110                                 dev_err(dev, "Failed to select page %d (%d)\n",
 111                                         page, status);
 112                                 mutex_unlock(&ee1004_bus_lock);
 113                                 return status;
 114                         }
 115                         dev_dbg(dev, "Selected page %d\n", page);
 116                         ee1004_current_page = page;
 117                 }
 118
 119                 status = ee1004_eeprom_read(client, buf, off, count);
 120                 if (status < 0) {
 121                         mutex_unlock(&ee1004_bus_lock);
 122                         return status;
 123                 }
 124                 buf += status;
 125                 off += status;
 126                 count -= status;
 127
 128                 if (off == EE1004_PAGE_SIZE) {
 129                         page++;
 130                         off = 0;
 131                 }
 132         }
 133
 134         mutex_unlock(&ee1004_bus_lock);
 135
 136         return requested;
 137 }
 138
 139 static const struct bin_attribute eeprom_attr = {
 140         .attr = {
 141                 .name = "eeprom",
 142                 .mode = 0444,
 143         },
 144         .size = EE1004_EEPROM_SIZE,
 145         .read = ee1004_read,
 146 };
 147
 148 static int ee1004_probe(struct i2c_client *client,
 149                         const struct i2c_device_id *id)
 150 {
 151         int err, cnr = 0;
 152         const char *slow = NULL;
 153
 154         /* Make sure we can operate on this adapter */
 155         if (!i2c_check_functionality(client->adapter,
 156                                      I2C_FUNC_SMBUS_READ_BYTE |
 157                                      I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 158                 if (i2c_check_functionality(client->adapter,
 159                                      I2C_FUNC_SMBUS_READ_BYTE |
 160                                      I2C_FUNC_SMBUS_READ_WORD_DATA))
 161                         slow = "word";
 162                 else if (i2c_check_functionality(client->adapter,
 163                                      I2C_FUNC_SMBUS_READ_BYTE |
 164                                      I2C_FUNC_SMBUS_READ_BYTE_DATA))
 165                         slow = "byte";
 166                 else
 167                         return -EPFNOSUPPORT;
 168         }
 169
 170         /* Use 2 dummy devices for page select command */
 171         mutex_lock(&ee1004_bus_lock);
 172         if (++ee1004_dev_count == 1) {
 173                 for (cnr = 0; cnr < 2; cnr++) {
 174                         ee1004_set_page[cnr] = i2c_new_dummy(client->adapter,
 175                                                 EE1004_ADDR_SET_PAGE + cnr);
 176                         if (!ee1004_set_page[cnr]) {
 177                                 dev_err(&client->dev,
 178                                         "address 0x%02x unavailable\n",
 179                                         EE1004_ADDR_SET_PAGE + cnr);
 180                                 err = -EADDRINUSE;
 181                                 goto err_clients;
 182                         }
 183                 }
 184         } else if (i2c_adapter_id(client->adapter) !=
 185                    i2c_adapter_id(ee1004_set_page[0]->adapter)) {
 186                 dev_err(&client->dev,
 187                         "Driver only supports devices on a single I2C bus\n");
 188                 err = -EOPNOTSUPP;
 189                 goto err_clients;
 190         }
 191
 192         /* Remember current page to avoid unneeded page select */
 193         err = i2c_smbus_read_byte(ee1004_set_page[0]);
 194         if (err == -ENXIO) {
 195                 /* Nack means page 1 is selected */
 196                 ee1004_current_page = 1;
 197         } else if (err < 0) {
 198                 /* Anything else is a real error, bail out */
 199                 goto err_clients;
 200         } else {
 201                 /* Ack means page 0 is selected, returned value meaningless */
 202                 ee1004_current_page = 0;
 203         }
 204         dev_dbg(&client->dev, "Currently selected page: %d\n",
 205                 ee1004_current_page);
 206         mutex_unlock(&ee1004_bus_lock);
 207
 208         /* Create the sysfs eeprom file */
 209         err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
 210         if (err)
 211                 goto err_clients_lock;
 212
 213         dev_info(&client->dev,
 214                  "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 215                  EE1004_EEPROM_SIZE);
 216         if (slow)
 217                 dev_notice(&client->dev,
 218                            "Falling back to %s reads, performance will suffer\n",
 219                            slow);
 220
 221         return 0;
 222
 223  err_clients_lock:
 224         mutex_lock(&ee1004_bus_lock);
 225  err_clients:
 226         if (--ee1004_dev_count == 0) {
 227                 for (cnr--; cnr >= 0; cnr--) {
 228                         i2c_unregister_device(ee1004_set_page[cnr]);
 229                         ee1004_set_page[cnr] = NULL;
 230                 }
 231         }
 232         mutex_unlock(&ee1004_bus_lock);
 233
 234         return err;
 235 }
 236
 237 static int ee1004_remove(struct i2c_client *client)
 238 {
 239         int i;
 240
 241         sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
 242
 243         /* Remove page select clients if this is the last device */
 244         mutex_lock(&ee1004_bus_lock);
 245         if (--ee1004_dev_count == 0) {
 246                 for (i = 0; i < 2; i++) {
 247                         i2c_unregister_device(ee1004_set_page[i]);
 248                         ee1004_set_page[i] = NULL;
 249                 }
 250         }
 251         mutex_unlock(&ee1004_bus_lock);
 252
 253         return 0;
 254 }
 255
 256 /*-------------------------------------------------------------------------*/
 257
 258 static struct i2c_driver ee1004_driver = {
 259         .driver = {
 260                 .name = "ee1004",
 261         },
 262         .probe = ee1004_probe,
 263         .remove = ee1004_remove,
 264         .id_table = ee1004_ids,
 265 };
 266
 267 static int __init ee1004_init(void)
 268 {
 269         return i2c_add_driver(&ee1004_driver);
 270 }
 271 module_init(ee1004_init);
 272
 273 static void __exit ee1004_exit(void)
 274 {
 275         i2c_del_driver(&ee1004_driver);
 276 }
 277 module_exit(ee1004_exit);
 278
 279 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 280 MODULE_AUTHOR("Jean Delvare");
 281 MODULE_LICENSE("GPL");