drivers/misc/eeprom/ee1004.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * ee1004 - driver for DDR4 SPD EEPROMs
   4  *
   5  * Copyright (C) 2017 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 ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
  57                                   unsigned int offset, size_t count)
  58 {
  59         int status;
  60
  61         if (count > I2C_SMBUS_BLOCK_MAX)
  62                 count = I2C_SMBUS_BLOCK_MAX;
  63         /* Can't cross page boundaries */
  64         if (unlikely(offset + count > EE1004_PAGE_SIZE))
  65                 count = EE1004_PAGE_SIZE - offset;
  66
  67         status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
  68                                                            count, buf);
  69         dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
  70
  71         return status;
  72 }
  73
  74 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
  75                            struct bin_attribute *bin_attr,
  76                            char *buf, loff_t off, size_t count)
  77 {
  78         struct device *dev = kobj_to_dev(kobj);
  79         struct i2c_client *client = to_i2c_client(dev);
  80         size_t requested = count;
  81         int page;
  82
  83         if (unlikely(!count))
  84                 return count;
  85
  86         page = off >> EE1004_PAGE_SHIFT;
  87         if (unlikely(page > 1))
  88                 return 0;
  89         off &= (1 << EE1004_PAGE_SHIFT) - 1;
  90
  91         /*
  92          * Read data from chip, protecting against concurrent access to
  93          * other EE1004 SPD EEPROMs on the same adapter.
  94          */
  95         mutex_lock(&ee1004_bus_lock);
  96
  97         while (count) {
  98                 int status;
  99
 100                 /* Select page */
 101                 if (page != ee1004_current_page) {
 102                         /* Data is ignored */
 103                         status = i2c_smbus_write_byte(ee1004_set_page[page],
 104                                                       0x00);
 105                         if (status < 0) {
 106                                 dev_err(dev, "Failed to select page %d (%d)\n",
 107                                         page, status);
 108                                 mutex_unlock(&ee1004_bus_lock);
 109                                 return status;
 110                         }
 111                         dev_dbg(dev, "Selected page %d\n", page);
 112                         ee1004_current_page = page;
 113                 }
 114
 115                 status = ee1004_eeprom_read(client, buf, off, count);
 116                 if (status < 0) {
 117                         mutex_unlock(&ee1004_bus_lock);
 118                         return status;
 119                 }
 120                 buf += status;
 121                 off += status;
 122                 count -= status;
 123
 124                 if (off == EE1004_PAGE_SIZE) {
 125                         page++;
 126                         off = 0;
 127                 }
 128         }
 129
 130         mutex_unlock(&ee1004_bus_lock);
 131
 132         return requested;
 133 }
 134
 135 static const struct bin_attribute eeprom_attr = {
 136         .attr = {
 137                 .name = "eeprom",
 138                 .mode = 0444,
 139         },
 140         .size = EE1004_EEPROM_SIZE,
 141         .read = ee1004_read,
 142 };
 143
 144 static int ee1004_probe(struct i2c_client *client,
 145                         const struct i2c_device_id *id)
 146 {
 147         int err, cnr = 0;
 148         const char *slow = NULL;
 149
 150         /* Make sure we can operate on this adapter */
 151         if (!i2c_check_functionality(client->adapter,
 152                                      I2C_FUNC_SMBUS_READ_BYTE |
 153                                      I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 154                 if (i2c_check_functionality(client->adapter,
 155                                      I2C_FUNC_SMBUS_READ_BYTE |
 156                                      I2C_FUNC_SMBUS_READ_WORD_DATA))
 157                         slow = "word";
 158                 else if (i2c_check_functionality(client->adapter,
 159                                      I2C_FUNC_SMBUS_READ_BYTE |
 160                                      I2C_FUNC_SMBUS_READ_BYTE_DATA))
 161                         slow = "byte";
 162                 else
 163                         return -EPFNOSUPPORT;
 164         }
 165
 166         /* Use 2 dummy devices for page select command */
 167         mutex_lock(&ee1004_bus_lock);
 168         if (++ee1004_dev_count == 1) {
 169                 for (cnr = 0; cnr < 2; cnr++) {
 170                         ee1004_set_page[cnr] = i2c_new_dummy(client->adapter,
 171                                                 EE1004_ADDR_SET_PAGE + cnr);
 172                         if (!ee1004_set_page[cnr]) {
 173                                 dev_err(&client->dev,
 174                                         "address 0x%02x unavailable\n",
 175                                         EE1004_ADDR_SET_PAGE + cnr);
 176                                 err = -EADDRINUSE;
 177                                 goto err_clients;
 178                         }
 179                 }
 180         } else if (i2c_adapter_id(client->adapter) !=
 181                    i2c_adapter_id(ee1004_set_page[0]->adapter)) {
 182                 dev_err(&client->dev,
 183                         "Driver only supports devices on a single I2C bus\n");
 184                 err = -EOPNOTSUPP;
 185                 goto err_clients;
 186         }
 187
 188         /* Remember current page to avoid unneeded page select */
 189         err = i2c_smbus_read_byte(ee1004_set_page[0]);
 190         if (err == -ENXIO) {
 191                 /* Nack means page 1 is selected */
 192                 ee1004_current_page = 1;
 193         } else if (err < 0) {
 194                 /* Anything else is a real error, bail out */
 195                 goto err_clients;
 196         } else {
 197                 /* Ack means page 0 is selected, returned value meaningless */
 198                 ee1004_current_page = 0;
 199         }
 200         dev_dbg(&client->dev, "Currently selected page: %d\n",
 201                 ee1004_current_page);
 202         mutex_unlock(&ee1004_bus_lock);
 203
 204         /* Create the sysfs eeprom file */
 205         err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
 206         if (err)
 207                 goto err_clients_lock;
 208
 209         dev_info(&client->dev,
 210                  "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 211                  EE1004_EEPROM_SIZE);
 212         if (slow)
 213                 dev_notice(&client->dev,
 214                            "Falling back to %s reads, performance will suffer\n",
 215                            slow);
 216
 217         return 0;
 218
 219  err_clients_lock:
 220         mutex_lock(&ee1004_bus_lock);
 221  err_clients:
 222         if (--ee1004_dev_count == 0) {
 223                 for (cnr--; cnr >= 0; cnr--) {
 224                         i2c_unregister_device(ee1004_set_page[cnr]);
 225                         ee1004_set_page[cnr] = NULL;
 226                 }
 227         }
 228         mutex_unlock(&ee1004_bus_lock);
 229
 230         return err;
 231 }
 232
 233 static int ee1004_remove(struct i2c_client *client)
 234 {
 235         int i;
 236
 237         sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
 238
 239         /* Remove page select clients if this is the last device */
 240         mutex_lock(&ee1004_bus_lock);
 241         if (--ee1004_dev_count == 0) {
 242                 for (i = 0; i < 2; i++) {
 243                         i2c_unregister_device(ee1004_set_page[i]);
 244                         ee1004_set_page[i] = NULL;
 245                 }
 246         }
 247         mutex_unlock(&ee1004_bus_lock);
 248
 249         return 0;
 250 }
 251
 252 /*-------------------------------------------------------------------------*/
 253
 254 static struct i2c_driver ee1004_driver = {
 255         .driver = {
 256                 .name = "ee1004",
 257         },
 258         .probe = ee1004_probe,
 259         .remove = ee1004_remove,
 260         .id_table = ee1004_ids,
 261 };
 262
 263 static int __init ee1004_init(void)
 264 {
 265         return i2c_add_driver(&ee1004_driver);
 266 }
 267 module_init(ee1004_init);
 268
 269 static void __exit ee1004_exit(void)
 270 {
 271         i2c_del_driver(&ee1004_driver);
 272 }
 273 module_exit(ee1004_exit);
 274
 275 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 276 MODULE_AUTHOR("Jean Delvare");
 277 MODULE_LICENSE("GPL");