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) 2017-2019 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 ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
  75                                   unsigned int offset, size_t count)
  76 {
  77         int status;
  78
  79         if (count > I2C_SMBUS_BLOCK_MAX)
  80                 count = I2C_SMBUS_BLOCK_MAX;
  81         /* Can't cross page boundaries */
  82         if (unlikely(offset + count > EE1004_PAGE_SIZE))
  83                 count = EE1004_PAGE_SIZE - offset;
  84
  85         status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
  86                                                            count, buf);
  87         dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
  88
  89         return status;
  90 }
  91
  92 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
  93                            struct bin_attribute *bin_attr,
  94                            char *buf, loff_t off, size_t count)
  95 {
  96         struct device *dev = kobj_to_dev(kobj);
  97         struct i2c_client *client = to_i2c_client(dev);
  98         size_t requested = count;
  99         int page;
 100
 101         if (unlikely(!count))
 102                 return count;
 103
 104         page = off >> EE1004_PAGE_SHIFT;
 105         if (unlikely(page > 1))
 106                 return 0;
 107         off &= (1 << EE1004_PAGE_SHIFT) - 1;
 108
 109         /*
 110          * Read data from chip, protecting against concurrent access to
 111          * other EE1004 SPD EEPROMs on the same adapter.
 112          */
 113         mutex_lock(&ee1004_bus_lock);
 114
 115         while (count) {
 116                 int status;
 117
 118                 /* Select page */
 119                 if (page != ee1004_current_page) {
 120                         /* Data is ignored */
 121                         status = i2c_smbus_write_byte(ee1004_set_page[page],
 122                                                       0x00);
 123                         if (status == -ENXIO) {
 124                                 /*
 125                                  * Don't give up just yet. Some memory
 126                                  * modules will select the page but not
 127                                  * ack the command. Check which page is
 128                                  * selected now.
 129                                  */
 130                                 if (ee1004_get_current_page() == page)
 131                                         status = 0;
 132                         }
 133                         if (status < 0) {
 134                                 dev_err(dev, "Failed to select page %d (%d)\n",
 135                                         page, status);
 136                                 mutex_unlock(&ee1004_bus_lock);
 137                                 return status;
 138                         }
 139                         dev_dbg(dev, "Selected page %d\n", page);
 140                         ee1004_current_page = page;
 141                 }
 142
 143                 status = ee1004_eeprom_read(client, buf, off, count);
 144                 if (status < 0) {
 145                         mutex_unlock(&ee1004_bus_lock);
 146                         return status;
 147                 }
 148                 buf += status;
 149                 off += status;
 150                 count -= status;
 151
 152                 if (off == EE1004_PAGE_SIZE) {
 153                         page++;
 154                         off = 0;
 155                 }
 156         }
 157
 158         mutex_unlock(&ee1004_bus_lock);
 159
 160         return requested;
 161 }
 162
 163 static const struct bin_attribute eeprom_attr = {
 164         .attr = {
 165                 .name = "eeprom",
 166                 .mode = 0444,
 167         },
 168         .size = EE1004_EEPROM_SIZE,
 169         .read = ee1004_read,
 170 };
 171
 172 static int ee1004_probe(struct i2c_client *client,
 173                         const struct i2c_device_id *id)
 174 {
 175         int err, cnr = 0;
 176         const char *slow = NULL;
 177
 178         /* Make sure we can operate on this adapter */
 179         if (!i2c_check_functionality(client->adapter,
 180                                      I2C_FUNC_SMBUS_READ_BYTE |
 181                                      I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 182                 if (i2c_check_functionality(client->adapter,
 183                                      I2C_FUNC_SMBUS_READ_BYTE |
 184                                      I2C_FUNC_SMBUS_READ_WORD_DATA))
 185                         slow = "word";
 186                 else if (i2c_check_functionality(client->adapter,
 187                                      I2C_FUNC_SMBUS_READ_BYTE |
 188                                      I2C_FUNC_SMBUS_READ_BYTE_DATA))
 189                         slow = "byte";
 190                 else
 191                         return -EPFNOSUPPORT;
 192         }
 193
 194         /* Use 2 dummy devices for page select command */
 195         mutex_lock(&ee1004_bus_lock);
 196         if (++ee1004_dev_count == 1) {
 197                 for (cnr = 0; cnr < 2; cnr++) {
 198                         ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
 199                                                 EE1004_ADDR_SET_PAGE + cnr);
 200                         if (IS_ERR(ee1004_set_page[cnr])) {
 201                                 dev_err(&client->dev,
 202                                         "address 0x%02x unavailable\n",
 203                                         EE1004_ADDR_SET_PAGE + cnr);
 204                                 err = PTR_ERR(ee1004_set_page[cnr]);
 205                                 goto err_clients;
 206                         }
 207                 }
 208         } else if (i2c_adapter_id(client->adapter) !=
 209                    i2c_adapter_id(ee1004_set_page[0]->adapter)) {
 210                 dev_err(&client->dev,
 211                         "Driver only supports devices on a single I2C bus\n");
 212                 err = -EOPNOTSUPP;
 213                 goto err_clients;
 214         }
 215
 216         /* Remember current page to avoid unneeded page select */
 217         err = ee1004_get_current_page();
 218         if (err < 0)
 219                 goto err_clients;
 220         ee1004_current_page = err;
 221         dev_dbg(&client->dev, "Currently selected page: %d\n",
 222                 ee1004_current_page);
 223         mutex_unlock(&ee1004_bus_lock);
 224
 225         /* Create the sysfs eeprom file */
 226         err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
 227         if (err)
 228                 goto err_clients_lock;
 229
 230         dev_info(&client->dev,
 231                  "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 232                  EE1004_EEPROM_SIZE);
 233         if (slow)
 234                 dev_notice(&client->dev,
 235                            "Falling back to %s reads, performance will suffer\n",
 236                            slow);
 237
 238         return 0;
 239
 240  err_clients_lock:
 241         mutex_lock(&ee1004_bus_lock);
 242  err_clients:
 243         if (--ee1004_dev_count == 0) {
 244                 for (cnr--; cnr >= 0; cnr--) {
 245                         i2c_unregister_device(ee1004_set_page[cnr]);
 246                         ee1004_set_page[cnr] = NULL;
 247                 }
 248         }
 249         mutex_unlock(&ee1004_bus_lock);
 250
 251         return err;
 252 }
 253
 254 static int ee1004_remove(struct i2c_client *client)
 255 {
 256         int i;
 257
 258         sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
 259
 260         /* Remove page select clients if this is the last device */
 261         mutex_lock(&ee1004_bus_lock);
 262         if (--ee1004_dev_count == 0) {
 263                 for (i = 0; i < 2; i++) {
 264                         i2c_unregister_device(ee1004_set_page[i]);
 265                         ee1004_set_page[i] = NULL;
 266                 }
 267         }
 268         mutex_unlock(&ee1004_bus_lock);
 269
 270         return 0;
 271 }
 272
 273 /*-------------------------------------------------------------------------*/
 274
 275 static struct i2c_driver ee1004_driver = {
 276         .driver = {
 277                 .name = "ee1004",
 278         },
 279         .probe = ee1004_probe,
 280         .remove = ee1004_remove,
 281         .id_table = ee1004_ids,
 282 };
 283 module_i2c_driver(ee1004_driver);
 284
 285 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 286 MODULE_AUTHOR("Jean Delvare");
 287 MODULE_LICENSE("GPL");