drivers/misc/eeprom/at24.c

   1 /*
   2  * at24.c - handle most I2C EEPROMs
   3  *
   4  * Copyright (C) 2005-2007 David Brownell
   5  * Copyright (C) 2008 Wolfram Sang, Pengutronix
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  */
  12 #include <linux/kernel.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/slab.h>
  16 #include <linux/delay.h>
  17 #include <linux/mutex.h>
  18 #include <linux/mod_devicetable.h>
  19 #include <linux/log2.h>
  20 #include <linux/bitops.h>
  21 #include <linux/jiffies.h>
  22 #include <linux/of.h>
  23 #include <linux/acpi.h>
  24 #include <linux/i2c.h>
  25 #include <linux/nvmem-provider.h>
  26 #include <linux/platform_data/at24.h>
  27
  28 /*
  29  * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
  30  * Differences between different vendor product lines (like Atmel AT24C or
  31  * MicroChip 24LC, etc) won't much matter for typical read/write access.
  32  * There are also I2C RAM chips, likewise interchangeable. One example
  33  * would be the PCF8570, which acts like a 24c02 EEPROM (256 bytes).
  34  *
  35  * However, misconfiguration can lose data. "Set 16-bit memory address"
  36  * to a part with 8-bit addressing will overwrite data. Writing with too
  37  * big a page size also loses data. And it's not safe to assume that the
  38  * conventional addresses 0x50..0x57 only hold eeproms; a PCF8563 RTC
  39  * uses 0x51, for just one example.
  40  *
  41  * Accordingly, explicit board-specific configuration data should be used
  42  * in almost all cases. (One partial exception is an SMBus used to access
  43  * "SPD" data for DRAM sticks. Those only use 24c02 EEPROMs.)
  44  *
  45  * So this driver uses "new style" I2C driver binding, expecting to be
  46  * told what devices exist. That may be in arch/X/mach-Y/board-Z.c or
  47  * similar kernel-resident tables; or, configuration data coming from
  48  * a bootloader.
  49  *
  50  * Other than binding model, current differences from "eeprom" driver are
  51  * that this one handles write access and isn't restricted to 24c02 devices.
  52  * It also handles larger devices (32 kbit and up) with two-byte addresses,
  53  * which won't work on pure SMBus systems.
  54  */
  55
  56 struct at24_data {
  57         struct at24_platform_data chip;
  58         int use_smbus;
  59         int use_smbus_write;
  60
  61         /*
  62          * Lock protects against activities from other Linux tasks,
  63          * but not from changes by other I2C masters.
  64          */
  65         struct mutex lock;
  66
  67         u8 *writebuf;
  68         unsigned write_max;
  69         unsigned num_addresses;
  70
  71         struct nvmem_config nvmem_config;
  72         struct nvmem_device *nvmem;
  73
  74         /*
  75          * Some chips tie up multiple I2C addresses; dummy devices reserve
  76          * them for us, and we'll use them with SMBus calls.
  77          */
  78         struct i2c_client *client[];
  79 };
  80
  81 /*
  82  * This parameter is to help this driver avoid blocking other drivers out
  83  * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
  84  * clock, one 256 byte read takes about 1/43 second which is excessive;
  85  * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
  86  * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
  87  *
  88  * This value is forced to be a power of two so that writes align on pages.
  89  */
  90 static unsigned io_limit = 128;
  91 module_param(io_limit, uint, 0);
  92 MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");
  93
  94 /*
  95  * Specs often allow 5 msec for a page write, sometimes 20 msec;
  96  * it's important to recover from write timeouts.
  97  */
  98 static unsigned write_timeout = 25;
  99 module_param(write_timeout, uint, 0);
 100 MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
 101
 102 #define AT24_SIZE_BYTELEN 5
 103 #define AT24_SIZE_FLAGS 8
 104
 105 #define AT24_BITMASK(x) (BIT(x) - 1)
 106
 107 /* create non-zero magic value for given eeprom parameters */
 108 #define AT24_DEVICE_MAGIC(_len, _flags)                 \
 109         ((1 << AT24_SIZE_FLAGS | (_flags))              \
 110             << AT24_SIZE_BYTELEN | ilog2(_len))
 111
 112 static const struct i2c_device_id at24_ids[] = {
 113         /* needs 8 addresses as A0-A2 are ignored */
 114         { "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },
 115         /* old variants can't be handled with this generic entry! */
 116         { "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
 117         { "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
 118         /* spd is a 24c02 in memory DIMMs */
 119         { "spd", AT24_DEVICE_MAGIC(2048 / 8,
 120                 AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
 121         { "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },
 122         /* 24rf08 quirk is handled at i2c-core */
 123         { "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },
 124         { "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },
 125         { "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },
 126         { "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },
 127         { "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },
 128         { "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },
 129         { "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },
 130         { "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },
 131         { "at24", 0 },
 132         { /* END OF LIST */ }
 133 };
 134 MODULE_DEVICE_TABLE(i2c, at24_ids);
 135
 136 static const struct acpi_device_id at24_acpi_ids[] = {
 137         { "INT3499", AT24_DEVICE_MAGIC(8192 / 8, 0) },
 138         { }
 139 };
 140 MODULE_DEVICE_TABLE(acpi, at24_acpi_ids);
 141
 142 /*-------------------------------------------------------------------------*/
 143
 144 /*
 145  * This routine supports chips which consume multiple I2C addresses. It
 146  * computes the addressing information to be used for a given r/w request.
 147  * Assumes that sanity checks for offset happened at sysfs-layer.
 148  */
 149 static struct i2c_client *at24_translate_offset(struct at24_data *at24,
 150                 unsigned *offset)
 151 {
 152         unsigned i;
 153
 154         if (at24->chip.flags & AT24_FLAG_ADDR16) {
 155                 i = *offset >> 16;
 156                 *offset &= 0xffff;
 157         } else {
 158                 i = *offset >> 8;
 159                 *offset &= 0xff;
 160         }
 161
 162         return at24->client[i];
 163 }
 164
 165 static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
 166                 unsigned offset, size_t count)
 167 {
 168         struct i2c_msg msg[2];
 169         u8 msgbuf[2];
 170         struct i2c_client *client;
 171         unsigned long timeout, read_time;
 172         int status, i;
 173
 174         memset(msg, 0, sizeof(msg));
 175
 176         /*
 177          * REVISIT some multi-address chips don't rollover page reads to
 178          * the next slave address, so we may need to truncate the count.
 179          * Those chips might need another quirk flag.
 180          *
 181          * If the real hardware used four adjacent 24c02 chips and that
 182          * were misconfigured as one 24c08, that would be a similar effect:
 183          * one "eeprom" file not four, but larger reads would fail when
 184          * they crossed certain pages.
 185          */
 186
 187         /*
 188          * Slave address and byte offset derive from the offset. Always
 189          * set the byte address; on a multi-master board, another master
 190          * may have changed the chip's "current" address pointer.
 191          */
 192         client = at24_translate_offset(at24, &offset);
 193
 194         if (count > io_limit)
 195                 count = io_limit;
 196
 197         if (at24->use_smbus) {
 198                 /* Smaller eeproms can work given some SMBus extension calls */
 199                 if (count > I2C_SMBUS_BLOCK_MAX)
 200                         count = I2C_SMBUS_BLOCK_MAX;
 201         } else {
 202                 /*
 203                  * When we have a better choice than SMBus calls, use a
 204                  * combined I2C message. Write address; then read up to
 205                  * io_limit data bytes. Note that read page rollover helps us
 206                  * here (unlike writes). msgbuf is u8 and will cast to our
 207                  * needs.
 208                  */
 209                 i = 0;
 210                 if (at24->chip.flags & AT24_FLAG_ADDR16)
 211                         msgbuf[i++] = offset >> 8;
 212                 msgbuf[i++] = offset;
 213
 214                 msg[0].addr = client->addr;
 215                 msg[0].buf = msgbuf;
 216                 msg[0].len = i;
 217
 218                 msg[1].addr = client->addr;
 219                 msg[1].flags = I2C_M_RD;
 220                 msg[1].buf = buf;
 221                 msg[1].len = count;
 222         }
 223
 224         /*
 225          * Reads fail if the previous write didn't complete yet. We may
 226          * loop a few times until this one succeeds, waiting at least
 227          * long enough for one entire page write to work.
 228          */
 229         timeout = jiffies + msecs_to_jiffies(write_timeout);
 230         do {
 231                 read_time = jiffies;
 232                 if (at24->use_smbus) {
 233                         status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
 234                                                                            count, buf);
 235                 } else {
 236                         status = i2c_transfer(client->adapter, msg, 2);
 237                         if (status == 2)
 238                                 status = count;
 239                 }
 240                 dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
 241                                 count, offset, status, jiffies);
 242
 243                 if (status == count)
 244                         return count;
 245
 246                 usleep_range(1000, 1500);
 247         } while (time_before(read_time, timeout));
 248
 249         return -ETIMEDOUT;
 250 }
 251
 252 static int at24_read(void *priv, unsigned int off, void *val, size_t count)
 253 {
 254         struct at24_data *at24 = priv;
 255         char *buf = val;
 256
 257         if (unlikely(!count))
 258                 return count;
 259
 260         /*
 261          * Read data from chip, protecting against concurrent updates
 262          * from this host, but not from other I2C masters.
 263          */
 264         mutex_lock(&at24->lock);
 265
 266         while (count) {
 267                 int     status;
 268
 269                 status = at24_eeprom_read(at24, buf, off, count);
 270                 if (status < 0) {
 271                         mutex_unlock(&at24->lock);
 272                         return status;
 273                 }
 274                 buf += status;
 275                 off += status;
 276                 count -= status;
 277         }
 278
 279         mutex_unlock(&at24->lock);
 280
 281         return 0;
 282 }
 283
 284 /*
 285  * Note that if the hardware write-protect pin is pulled high, the whole
 286  * chip is normally write protected. But there are plenty of product
 287  * variants here, including OTP fuses and partial chip protect.
 288  *
 289  * We only use page mode writes; the alternative is sloooow. This routine
 290  * writes at most one page.
 291  */
 292 static ssize_t at24_eeprom_write(struct at24_data *at24, const char *buf,
 293                 unsigned offset, size_t count)
 294 {
 295         struct i2c_client *client;
 296         struct i2c_msg msg;
 297         ssize_t status = 0;
 298         unsigned long timeout, write_time;
 299         unsigned next_page;
 300
 301         /* Get corresponding I2C address and adjust offset */
 302         client = at24_translate_offset(at24, &offset);
 303
 304         /* write_max is at most a page */
 305         if (count > at24->write_max)
 306                 count = at24->write_max;
 307
 308         /* Never roll over backwards, to the start of this page */
 309         next_page = roundup(offset + 1, at24->chip.page_size);
 310         if (offset + count > next_page)
 311                 count = next_page - offset;
 312
 313         /* If we'll use I2C calls for I/O, set up the message */
 314         if (!at24->use_smbus) {
 315                 int i = 0;
 316
 317                 msg.addr = client->addr;
 318                 msg.flags = 0;
 319
 320                 /* msg.buf is u8 and casts will mask the values */
 321                 msg.buf = at24->writebuf;
 322                 if (at24->chip.flags & AT24_FLAG_ADDR16)
 323                         msg.buf[i++] = offset >> 8;
 324
 325                 msg.buf[i++] = offset;
 326                 memcpy(&msg.buf[i], buf, count);
 327                 msg.len = i + count;
 328         }
 329
 330         /*
 331          * Writes fail if the previous one didn't complete yet. We may
 332          * loop a few times until this one succeeds, waiting at least
 333          * long enough for one entire page write to work.
 334          */
 335         timeout = jiffies + msecs_to_jiffies(write_timeout);
 336         do {
 337                 write_time = jiffies;
 338                 if (at24->use_smbus_write) {
 339                         switch (at24->use_smbus_write) {
 340                         case I2C_SMBUS_I2C_BLOCK_DATA:
 341                                 status = i2c_smbus_write_i2c_block_data(client,
 342                                                 offset, count, buf);
 343                                 break;
 344                         case I2C_SMBUS_BYTE_DATA:
 345                                 status = i2c_smbus_write_byte_data(client,
 346                                                 offset, buf[0]);
 347                                 break;
 348                         }
 349
 350                         if (status == 0)
 351                                 status = count;
 352                 } else {
 353                         status = i2c_transfer(client->adapter, &msg, 1);
 354                         if (status == 1)
 355                                 status = count;
 356                 }
 357                 dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
 358                                 count, offset, status, jiffies);
 359
 360                 if (status == count)
 361                         return count;
 362
 363                 usleep_range(1000, 1500);
 364         } while (time_before(write_time, timeout));
 365
 366         return -ETIMEDOUT;
 367 }
 368
 369 static int at24_write(void *priv, unsigned int off, void *val, size_t count)
 370 {
 371         struct at24_data *at24 = priv;
 372         char *buf = val;
 373
 374         if (unlikely(!count))
 375                 return -EINVAL;
 376
 377         /*
 378          * Write data to chip, protecting against concurrent updates
 379          * from this host, but not from other I2C masters.
 380          */
 381         mutex_lock(&at24->lock);
 382
 383         while (count) {
 384                 int status;
 385
 386                 status = at24_eeprom_write(at24, buf, off, count);
 387                 if (status < 0) {
 388                         mutex_unlock(&at24->lock);
 389                         return status;
 390                 }
 391                 buf += status;
 392                 off += status;
 393                 count -= status;
 394         }
 395
 396         mutex_unlock(&at24->lock);
 397
 398         return 0;
 399 }
 400
 401 #ifdef CONFIG_OF
 402 static void at24_get_ofdata(struct i2c_client *client,
 403                 struct at24_platform_data *chip)
 404 {
 405         const __be32 *val;
 406         struct device_node *node = client->dev.of_node;
 407
 408         if (node) {
 409                 if (of_get_property(node, "read-only", NULL))
 410                         chip->flags |= AT24_FLAG_READONLY;
 411                 val = of_get_property(node, "pagesize", NULL);
 412                 if (val)
 413                         chip->page_size = be32_to_cpup(val);
 414         }
 415 }
 416 #else
 417 static void at24_get_ofdata(struct i2c_client *client,
 418                 struct at24_platform_data *chip)
 419 { }
 420 #endif /* CONFIG_OF */
 421
 422 static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 423 {
 424         struct at24_platform_data chip;
 425         kernel_ulong_t magic = 0;
 426         bool writable;
 427         int use_smbus = 0;
 428         int use_smbus_write = 0;
 429         struct at24_data *at24;
 430         int err;
 431         unsigned i, num_addresses;
 432
 433         if (client->dev.platform_data) {
 434                 chip = *(struct at24_platform_data *)client->dev.platform_data;
 435         } else {
 436                 if (id) {
 437                         magic = id->driver_data;
 438                 } else {
 439                         const struct acpi_device_id *aid;
 440
 441                         aid = acpi_match_device(at24_acpi_ids, &client->dev);
 442                         if (aid)
 443                                 magic = aid->driver_data;
 444                 }
 445                 if (!magic)
 446                         return -ENODEV;
 447
 448                 chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
 449                 magic >>= AT24_SIZE_BYTELEN;
 450                 chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
 451                 /*
 452                  * This is slow, but we can't know all eeproms, so we better
 453                  * play safe. Specifying custom eeprom-types via platform_data
 454                  * is recommended anyhow.
 455                  */
 456                 chip.page_size = 1;
 457
 458                 /* update chipdata if OF is present */
 459                 at24_get_ofdata(client, &chip);
 460
 461                 chip.setup = NULL;
 462                 chip.context = NULL;
 463         }
 464
 465         if (!is_power_of_2(chip.byte_len))
 466                 dev_warn(&client->dev,
 467                         "byte_len looks suspicious (no power of 2)!\n");
 468         if (!chip.page_size) {
 469                 dev_err(&client->dev, "page_size must not be 0!\n");
 470                 return -EINVAL;
 471         }
 472         if (!is_power_of_2(chip.page_size))
 473                 dev_warn(&client->dev,
 474                         "page_size looks suspicious (no power of 2)!\n");
 475
 476         /* Use I2C operations unless we're stuck with SMBus extensions. */
 477         if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 478                 if (chip.flags & AT24_FLAG_ADDR16)
 479                         return -EPFNOSUPPORT;
 480
 481                 if (i2c_check_functionality(client->adapter,
 482                                 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 483                         use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
 484                 } else if (i2c_check_functionality(client->adapter,
 485                                 I2C_FUNC_SMBUS_READ_WORD_DATA)) {
 486                         use_smbus = I2C_SMBUS_WORD_DATA;
 487                 } else if (i2c_check_functionality(client->adapter,
 488                                 I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
 489                         use_smbus = I2C_SMBUS_BYTE_DATA;
 490                 } else {
 491                         return -EPFNOSUPPORT;
 492                 }
 493
 494                 if (i2c_check_functionality(client->adapter,
 495                                 I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
 496                         use_smbus_write = I2C_SMBUS_I2C_BLOCK_DATA;
 497                 } else if (i2c_check_functionality(client->adapter,
 498                                 I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {
 499                         use_smbus_write = I2C_SMBUS_BYTE_DATA;
 500                         chip.page_size = 1;
 501                 }
 502         }
 503
 504         if (chip.flags & AT24_FLAG_TAKE8ADDR)
 505                 num_addresses = 8;
 506         else
 507                 num_addresses = DIV_ROUND_UP(chip.byte_len,
 508                         (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
 509
 510         at24 = devm_kzalloc(&client->dev, sizeof(struct at24_data) +
 511                 num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
 512         if (!at24)
 513                 return -ENOMEM;
 514
 515         mutex_init(&at24->lock);
 516         at24->use_smbus = use_smbus;
 517         at24->use_smbus_write = use_smbus_write;
 518         at24->chip = chip;
 519         at24->num_addresses = num_addresses;
 520
 521         writable = !(chip.flags & AT24_FLAG_READONLY);
 522         if (writable) {
 523                 if (!use_smbus || use_smbus_write) {
 524
 525                         unsigned write_max = chip.page_size;
 526
 527                         if (write_max > io_limit)
 528                                 write_max = io_limit;
 529                         if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
 530                                 write_max = I2C_SMBUS_BLOCK_MAX;
 531                         at24->write_max = write_max;
 532
 533                         /* buffer (data + address at the beginning) */
 534                         at24->writebuf = devm_kzalloc(&client->dev,
 535                                 write_max + 2, GFP_KERNEL);
 536                         if (!at24->writebuf)
 537                                 return -ENOMEM;
 538                 } else {
 539                         dev_warn(&client->dev,
 540                                 "cannot write due to controller restrictions.");
 541                 }
 542         }
 543
 544         at24->client[0] = client;
 545
 546         /* use dummy devices for multiple-address chips */
 547         for (i = 1; i < num_addresses; i++) {
 548                 at24->client[i] = i2c_new_dummy(client->adapter,
 549                                         client->addr + i);
 550                 if (!at24->client[i]) {
 551                         dev_err(&client->dev, "address 0x%02x unavailable\n",
 552                                         client->addr + i);
 553                         err = -EADDRINUSE;
 554                         goto err_clients;
 555                 }
 556         }
 557
 558         at24->nvmem_config.name = dev_name(&client->dev);
 559         at24->nvmem_config.dev = &client->dev;
 560         at24->nvmem_config.read_only = !writable;
 561         at24->nvmem_config.root_only = true;
 562         at24->nvmem_config.owner = THIS_MODULE;
 563         at24->nvmem_config.compat = true;
 564         at24->nvmem_config.base_dev = &client->dev;
 565         at24->nvmem_config.reg_read = at24_read;
 566         at24->nvmem_config.reg_write = at24_write;
 567         at24->nvmem_config.priv = at24;
 568         at24->nvmem_config.stride = 4;
 569         at24->nvmem_config.word_size = 1;
 570         at24->nvmem_config.size = chip.byte_len;
 571
 572         at24->nvmem = nvmem_register(&at24->nvmem_config);
 573
 574         if (IS_ERR(at24->nvmem)) {
 575                 err = PTR_ERR(at24->nvmem);
 576                 goto err_clients;
 577         }
 578
 579         i2c_set_clientdata(client, at24);
 580
 581         dev_info(&client->dev, "%u byte %s EEPROM, %s, %u bytes/write\n",
 582                 chip.byte_len, client->name,
 583                 writable ? "writable" : "read-only", at24->write_max);
 584         if (use_smbus == I2C_SMBUS_WORD_DATA ||
 585             use_smbus == I2C_SMBUS_BYTE_DATA) {
 586                 dev_notice(&client->dev, "Falling back to %s reads, "
 587                            "performance will suffer\n", use_smbus ==
 588                            I2C_SMBUS_WORD_DATA ? "word" : "byte");
 589         }
 590
 591         /* export data to kernel code */
 592         if (chip.setup)
 593                 chip.setup(at24->nvmem, chip.context);
 594
 595         return 0;
 596
 597 err_clients:
 598         for (i = 1; i < num_addresses; i++)
 599                 if (at24->client[i])
 600                         i2c_unregister_device(at24->client[i]);
 601
 602         return err;
 603 }
 604
 605 static int at24_remove(struct i2c_client *client)
 606 {
 607         struct at24_data *at24;
 608         int i;
 609
 610         at24 = i2c_get_clientdata(client);
 611
 612         nvmem_unregister(at24->nvmem);
 613
 614         for (i = 1; i < at24->num_addresses; i++)
 615                 i2c_unregister_device(at24->client[i]);
 616
 617         return 0;
 618 }
 619
 620 /*-------------------------------------------------------------------------*/
 621
 622 static struct i2c_driver at24_driver = {
 623         .driver = {
 624                 .name = "at24",
 625                 .acpi_match_table = ACPI_PTR(at24_acpi_ids),
 626         },
 627         .probe = at24_probe,
 628         .remove = at24_remove,
 629         .id_table = at24_ids,
 630 };
 631
 632 static int __init at24_init(void)
 633 {
 634         if (!io_limit) {
 635                 pr_err("at24: io_limit must not be 0!\n");
 636                 return -EINVAL;
 637         }
 638
 639         io_limit = rounddown_pow_of_two(io_limit);
 640         return i2c_add_driver(&at24_driver);
 641 }
 642 module_init(at24_init);
 643
 644 static void __exit at24_exit(void)
 645 {
 646         i2c_del_driver(&at24_driver);
 647 }
 648 module_exit(at24_exit);
 649
 650 MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
 651 MODULE_AUTHOR("David Brownell and Wolfram Sang");
 652 MODULE_LICENSE("GPL");