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/sysfs.h>
  19 #include <linux/mod_devicetable.h>
  20 #include <linux/log2.h>
  21 #include <linux/bitops.h>
  22 #include <linux/jiffies.h>
  23 #include <linux/i2c.h>
  24 #include <linux/i2c/at24.h>
  25
  26 /*
  27  * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
  28  * Differences between different vendor product lines (like Atmel AT24C or
  29  * MicroChip 24LC, etc) won't much matter for typical read/write access.
  30  * There are also I2C RAM chips, likewise interchangeable. One example
  31  * would be the PCF8570, which acts like a 24c02 EEPROM (256 bytes).
  32  *
  33  * However, misconfiguration can lose data. "Set 16-bit memory address"
  34  * to a part with 8-bit addressing will overwrite data. Writing with too
  35  * big a page size also loses data. And it's not safe to assume that the
  36  * conventional addresses 0x50..0x57 only hold eeproms; a PCF8563 RTC
  37  * uses 0x51, for just one example.
  38  *
  39  * Accordingly, explicit board-specific configuration data should be used
  40  * in almost all cases. (One partial exception is an SMBus used to access
  41  * "SPD" data for DRAM sticks. Those only use 24c02 EEPROMs.)
  42  *
  43  * So this driver uses "new style" I2C driver binding, expecting to be
  44  * told what devices exist. That may be in arch/X/mach-Y/board-Z.c or
  45  * similar kernel-resident tables; or, configuration data coming from
  46  * a bootloader.
  47  *
  48  * Other than binding model, current differences from "eeprom" driver are
  49  * that this one handles write access and isn't restricted to 24c02 devices.
  50  * It also handles larger devices (32 kbit and up) with two-byte addresses,
  51  * which won't work on pure SMBus systems.
  52  */
  53
  54 struct at24_data {
  55         struct at24_platform_data chip;
  56         struct memory_accessor macc;
  57         bool use_smbus;
  58
  59         /*
  60          * Lock protects against activities from other Linux tasks,
  61          * but not from changes by other I2C masters.
  62          */
  63         struct mutex lock;
  64         struct bin_attribute bin;
  65
  66         u8 *writebuf;
  67         unsigned write_max;
  68         unsigned num_addresses;
  69
  70         /*
  71          * Some chips tie up multiple I2C addresses; dummy devices reserve
  72          * them for us, and we'll use them with SMBus calls.
  73          */
  74         struct i2c_client *client[];
  75 };
  76
  77 /*
  78  * This parameter is to help this driver avoid blocking other drivers out
  79  * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
  80  * clock, one 256 byte read takes about 1/43 second which is excessive;
  81  * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
  82  * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
  83  *
  84  * This value is forced to be a power of two so that writes align on pages.
  85  */
  86 static unsigned io_limit = 128;
  87 module_param(io_limit, uint, 0);
  88 MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");
  89
  90 /*
  91  * Specs often allow 5 msec for a page write, sometimes 20 msec;
  92  * it's important to recover from write timeouts.
  93  */
  94 static unsigned write_timeout = 25;
  95 module_param(write_timeout, uint, 0);
  96 MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
  97
  98 #define AT24_SIZE_BYTELEN 5
  99 #define AT24_SIZE_FLAGS 8
 100
 101 #define AT24_BITMASK(x) (BIT(x) - 1)
 102
 103 /* create non-zero magic value for given eeprom parameters */
 104 #define AT24_DEVICE_MAGIC(_len, _flags)                 \
 105         ((1 << AT24_SIZE_FLAGS | (_flags))              \
 106             << AT24_SIZE_BYTELEN | ilog2(_len))
 107
 108 static const struct i2c_device_id at24_ids[] = {
 109         /* needs 8 addresses as A0-A2 are ignored */
 110         { "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },
 111         /* old variants can't be handled with this generic entry! */
 112         { "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
 113         { "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
 114         /* spd is a 24c02 in memory DIMMs */
 115         { "spd", AT24_DEVICE_MAGIC(2048 / 8,
 116                 AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
 117         { "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },
 118         /* 24rf08 quirk is handled at i2c-core */
 119         { "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },
 120         { "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },
 121         { "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },
 122         { "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },
 123         { "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },
 124         { "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },
 125         { "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },
 126         { "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },
 127         { "at24", 0 },
 128         { /* END OF LIST */ }
 129 };
 130 MODULE_DEVICE_TABLE(i2c, at24_ids);
 131
 132 /*-------------------------------------------------------------------------*/
 133
 134 /*
 135  * This routine supports chips which consume multiple I2C addresses. It
 136  * computes the addressing information to be used for a given r/w request.
 137  * Assumes that sanity checks for offset happened at sysfs-layer.
 138  */
 139 static struct i2c_client *at24_translate_offset(struct at24_data *at24,
 140                 unsigned *offset)
 141 {
 142         unsigned i;
 143
 144         if (at24->chip.flags & AT24_FLAG_ADDR16) {
 145                 i = *offset >> 16;
 146                 *offset &= 0xffff;
 147         } else {
 148                 i = *offset >> 8;
 149                 *offset &= 0xff;
 150         }
 151
 152         return at24->client[i];
 153 }
 154
 155 static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
 156                 unsigned offset, size_t count)
 157 {
 158         struct i2c_msg msg[2];
 159         u8 msgbuf[2];
 160         struct i2c_client *client;
 161         int status, i;
 162
 163         memset(msg, 0, sizeof(msg));
 164
 165         /*
 166          * REVISIT some multi-address chips don't rollover page reads to
 167          * the next slave address, so we may need to truncate the count.
 168          * Those chips might need another quirk flag.
 169          *
 170          * If the real hardware used four adjacent 24c02 chips and that
 171          * were misconfigured as one 24c08, that would be a similar effect:
 172          * one "eeprom" file not four, but larger reads would fail when
 173          * they crossed certain pages.
 174          */
 175
 176         /*
 177          * Slave address and byte offset derive from the offset. Always
 178          * set the byte address; on a multi-master board, another master
 179          * may have changed the chip's "current" address pointer.
 180          */
 181         client = at24_translate_offset(at24, &offset);
 182
 183         if (count > io_limit)
 184                 count = io_limit;
 185
 186         /* Smaller eeproms can work given some SMBus extension calls */
 187         if (at24->use_smbus) {
 188                 if (count > I2C_SMBUS_BLOCK_MAX)
 189                         count = I2C_SMBUS_BLOCK_MAX;
 190                 status = i2c_smbus_read_i2c_block_data(client, offset,
 191                                 count, buf);
 192                 dev_dbg(&client->dev, "smbus read %zu@%d --> %d\n",
 193                                 count, offset, status);
 194                 return (status < 0) ? -EIO : status;
 195         }
 196
 197         /*
 198          * When we have a better choice than SMBus calls, use a combined
 199          * I2C message. Write address; then read up to io_limit data bytes.
 200          * Note that read page rollover helps us here (unlike writes).
 201          * msgbuf is u8 and will cast to our needs.
 202          */
 203         i = 0;
 204         if (at24->chip.flags & AT24_FLAG_ADDR16)
 205                 msgbuf[i++] = offset >> 8;
 206         msgbuf[i++] = offset;
 207
 208         msg[0].addr = client->addr;
 209         msg[0].buf = msgbuf;
 210         msg[0].len = i;
 211
 212         msg[1].addr = client->addr;
 213         msg[1].flags = I2C_M_RD;
 214         msg[1].buf = buf;
 215         msg[1].len = count;
 216
 217         status = i2c_transfer(client->adapter, msg, 2);
 218         dev_dbg(&client->dev, "i2c read %zu@%d --> %d\n",
 219                         count, offset, status);
 220
 221         if (status == 2)
 222                 return count;
 223         else if (status >= 0)
 224                 return -EIO;
 225         else
 226                 return status;
 227 }
 228
 229 static ssize_t at24_read(struct at24_data *at24,
 230                 char *buf, loff_t off, size_t count)
 231 {
 232         ssize_t retval = 0;
 233
 234         if (unlikely(!count))
 235                 return count;
 236
 237         /*
 238          * Read data from chip, protecting against concurrent updates
 239          * from this host, but not from other I2C masters.
 240          */
 241         mutex_lock(&at24->lock);
 242
 243         while (count) {
 244                 ssize_t status;
 245
 246                 status = at24_eeprom_read(at24, buf, off, count);
 247                 if (status <= 0) {
 248                         if (retval == 0)
 249                                 retval = status;
 250                         break;
 251                 }
 252                 buf += status;
 253                 off += status;
 254                 count -= status;
 255                 retval += status;
 256         }
 257
 258         mutex_unlock(&at24->lock);
 259
 260         return retval;
 261 }
 262
 263 static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
 264                 char *buf, loff_t off, size_t count)
 265 {
 266         struct at24_data *at24;
 267
 268         at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 269         return at24_read(at24, buf, off, count);
 270 }
 271
 272
 273 /*
 274  * Note that if the hardware write-protect pin is pulled high, the whole
 275  * chip is normally write protected. But there are plenty of product
 276  * variants here, including OTP fuses and partial chip protect.
 277  *
 278  * We only use page mode writes; the alternative is sloooow. This routine
 279  * writes at most one page.
 280  */
 281 static ssize_t at24_eeprom_write(struct at24_data *at24, char *buf,
 282                 unsigned offset, size_t count)
 283 {
 284         struct i2c_client *client;
 285         struct i2c_msg msg;
 286         ssize_t status;
 287         unsigned long timeout, write_time;
 288         unsigned next_page;
 289
 290         /* Get corresponding I2C address and adjust offset */
 291         client = at24_translate_offset(at24, &offset);
 292
 293         /* write_max is at most a page */
 294         if (count > at24->write_max)
 295                 count = at24->write_max;
 296
 297         /* Never roll over backwards, to the start of this page */
 298         next_page = roundup(offset + 1, at24->chip.page_size);
 299         if (offset + count > next_page)
 300                 count = next_page - offset;
 301
 302         /* If we'll use I2C calls for I/O, set up the message */
 303         if (!at24->use_smbus) {
 304                 int i = 0;
 305
 306                 msg.addr = client->addr;
 307                 msg.flags = 0;
 308
 309                 /* msg.buf is u8 and casts will mask the values */
 310                 msg.buf = at24->writebuf;
 311                 if (at24->chip.flags & AT24_FLAG_ADDR16)
 312                         msg.buf[i++] = offset >> 8;
 313
 314                 msg.buf[i++] = offset;
 315                 memcpy(&msg.buf[i], buf, count);
 316                 msg.len = i + count;
 317         }
 318
 319         /*
 320          * Writes fail if the previous one didn't complete yet. We may
 321          * loop a few times until this one succeeds, waiting at least
 322          * long enough for one entire page write to work.
 323          */
 324         timeout = jiffies + msecs_to_jiffies(write_timeout);
 325         do {
 326                 write_time = jiffies;
 327                 if (at24->use_smbus) {
 328                         status = i2c_smbus_write_i2c_block_data(client,
 329                                         offset, count, buf);
 330                         if (status == 0)
 331                                 status = count;
 332                 } else {
 333                         status = i2c_transfer(client->adapter, &msg, 1);
 334                         if (status == 1)
 335                                 status = count;
 336                 }
 337                 dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
 338                                 count, offset, status, jiffies);
 339
 340                 if (status == count)
 341                         return count;
 342
 343                 /* REVISIT: at HZ=100, this is sloooow */
 344                 msleep(1);
 345         } while (time_before(write_time, timeout));
 346
 347         return -ETIMEDOUT;
 348 }
 349
 350 static ssize_t at24_write(struct at24_data *at24,
 351                 char *buf, loff_t off, size_t count)
 352 {
 353         ssize_t retval = 0;
 354
 355         if (unlikely(!count))
 356                 return count;
 357
 358         /*
 359          * Write data to chip, protecting against concurrent updates
 360          * from this host, but not from other I2C masters.
 361          */
 362         mutex_lock(&at24->lock);
 363
 364         while (count) {
 365                 ssize_t status;
 366
 367                 status = at24_eeprom_write(at24, buf, off, count);
 368                 if (status <= 0) {
 369                         if (retval == 0)
 370                                 retval = status;
 371                         break;
 372                 }
 373                 buf += status;
 374                 off += status;
 375                 count -= status;
 376                 retval += status;
 377         }
 378
 379         mutex_unlock(&at24->lock);
 380
 381         return retval;
 382 }
 383
 384 static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
 385                 char *buf, loff_t off, size_t count)
 386 {
 387         struct at24_data *at24;
 388
 389         at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 390         return at24_write(at24, buf, off, count);
 391 }
 392
 393 /*-------------------------------------------------------------------------*/
 394
 395 /*
 396  * This lets other kernel code access the eeprom data. For example, it
 397  * might hold a board's Ethernet address, or board-specific calibration
 398  * data generated on the manufacturing floor.
 399  */
 400
 401 static ssize_t at24_macc_read(struct memory_accessor *macc, char *buf,
 402                          off_t offset, size_t count)
 403 {
 404         struct at24_data *at24 = container_of(macc, struct at24_data, macc);
 405
 406         return at24_read(at24, buf, offset, count);
 407 }
 408
 409 static ssize_t at24_macc_write(struct memory_accessor *macc, char *buf,
 410                           off_t offset, size_t count)
 411 {
 412         struct at24_data *at24 = container_of(macc, struct at24_data, macc);
 413
 414         return at24_write(at24, buf, offset, count);
 415 }
 416
 417 /*-------------------------------------------------------------------------*/
 418
 419 static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 420 {
 421         struct at24_platform_data chip;
 422         bool writable;
 423         bool use_smbus = false;
 424         struct at24_data *at24;
 425         int err;
 426         unsigned i, num_addresses;
 427         kernel_ulong_t magic;
 428
 429         if (client->dev.platform_data) {
 430                 chip = *(struct at24_platform_data *)client->dev.platform_data;
 431         } else {
 432                 if (!id->driver_data) {
 433                         err = -ENODEV;
 434                         goto err_out;
 435                 }
 436                 magic = id->driver_data;
 437                 chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
 438                 magic >>= AT24_SIZE_BYTELEN;
 439                 chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
 440                 /*
 441                  * This is slow, but we can't know all eeproms, so we better
 442                  * play safe. Specifying custom eeprom-types via platform_data
 443                  * is recommended anyhow.
 444                  */
 445                 chip.page_size = 1;
 446
 447                 chip.setup = NULL;
 448                 chip.context = NULL;
 449         }
 450
 451         if (!is_power_of_2(chip.byte_len))
 452                 dev_warn(&client->dev,
 453                         "byte_len looks suspicious (no power of 2)!\n");
 454         if (!is_power_of_2(chip.page_size))
 455                 dev_warn(&client->dev,
 456                         "page_size looks suspicious (no power of 2)!\n");
 457
 458         /* Use I2C operations unless we're stuck with SMBus extensions. */
 459         if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 460                 if (chip.flags & AT24_FLAG_ADDR16) {
 461                         err = -EPFNOSUPPORT;
 462                         goto err_out;
 463                 }
 464                 if (!i2c_check_functionality(client->adapter,
 465                                 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 466                         err = -EPFNOSUPPORT;
 467                         goto err_out;
 468                 }
 469                 use_smbus = true;
 470         }
 471
 472         if (chip.flags & AT24_FLAG_TAKE8ADDR)
 473                 num_addresses = 8;
 474         else
 475                 num_addresses = DIV_ROUND_UP(chip.byte_len,
 476                         (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
 477
 478         at24 = kzalloc(sizeof(struct at24_data) +
 479                 num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
 480         if (!at24) {
 481                 err = -ENOMEM;
 482                 goto err_out;
 483         }
 484
 485         mutex_init(&at24->lock);
 486         at24->use_smbus = use_smbus;
 487         at24->chip = chip;
 488         at24->num_addresses = num_addresses;
 489
 490         /*
 491          * Export the EEPROM bytes through sysfs, since that's convenient.
 492          * By default, only root should see the data (maybe passwords etc)
 493          */
 494         at24->bin.attr.name = "eeprom";
 495         at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
 496         at24->bin.read = at24_bin_read;
 497         at24->bin.size = chip.byte_len;
 498
 499         at24->macc.read = at24_macc_read;
 500
 501         writable = !(chip.flags & AT24_FLAG_READONLY);
 502         if (writable) {
 503                 if (!use_smbus || i2c_check_functionality(client->adapter,
 504                                 I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
 505
 506                         unsigned write_max = chip.page_size;
 507
 508                         at24->macc.write = at24_macc_write;
 509
 510                         at24->bin.write = at24_bin_write;
 511                         at24->bin.attr.mode |= S_IWUSR;
 512
 513                         if (write_max > io_limit)
 514                                 write_max = io_limit;
 515                         if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
 516                                 write_max = I2C_SMBUS_BLOCK_MAX;
 517                         at24->write_max = write_max;
 518
 519                         /* buffer (data + address at the beginning) */
 520                         at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
 521                         if (!at24->writebuf) {
 522                                 err = -ENOMEM;
 523                                 goto err_struct;
 524                         }
 525                 } else {
 526                         dev_warn(&client->dev,
 527                                 "cannot write due to controller restrictions.");
 528                 }
 529         }
 530
 531         at24->client[0] = client;
 532
 533         /* use dummy devices for multiple-address chips */
 534         for (i = 1; i < num_addresses; i++) {
 535                 at24->client[i] = i2c_new_dummy(client->adapter,
 536                                         client->addr + i);
 537                 if (!at24->client[i]) {
 538                         dev_err(&client->dev, "address 0x%02x unavailable\n",
 539                                         client->addr + i);
 540                         err = -EADDRINUSE;
 541                         goto err_clients;
 542                 }
 543         }
 544
 545         err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
 546         if (err)
 547                 goto err_clients;
 548
 549         i2c_set_clientdata(client, at24);
 550
 551         dev_info(&client->dev, "%zu byte %s EEPROM %s\n",
 552                 at24->bin.size, client->name,
 553                 writable ? "(writable)" : "(read-only)");
 554         dev_dbg(&client->dev,
 555                 "page_size %d, num_addresses %d, write_max %d%s\n",
 556                 chip.page_size, num_addresses,
 557                 at24->write_max,
 558                 use_smbus ? ", use_smbus" : "");
 559
 560         /* export data to kernel code */
 561         if (chip.setup)
 562                 chip.setup(&at24->macc, chip.context);
 563
 564         return 0;
 565
 566 err_clients:
 567         for (i = 1; i < num_addresses; i++)
 568                 if (at24->client[i])
 569                         i2c_unregister_device(at24->client[i]);
 570
 571         kfree(at24->writebuf);
 572 err_struct:
 573         kfree(at24);
 574 err_out:
 575         dev_dbg(&client->dev, "probe error %d\n", err);
 576         return err;
 577 }
 578
 579 static int __devexit at24_remove(struct i2c_client *client)
 580 {
 581         struct at24_data *at24;
 582         int i;
 583
 584         at24 = i2c_get_clientdata(client);
 585         sysfs_remove_bin_file(&client->dev.kobj, &at24->bin);
 586
 587         for (i = 1; i < at24->num_addresses; i++)
 588                 i2c_unregister_device(at24->client[i]);
 589
 590         kfree(at24->writebuf);
 591         kfree(at24);
 592         i2c_set_clientdata(client, NULL);
 593         return 0;
 594 }
 595
 596 /*-------------------------------------------------------------------------*/
 597
 598 static struct i2c_driver at24_driver = {
 599         .driver = {
 600                 .name = "at24",
 601                 .owner = THIS_MODULE,
 602         },
 603         .probe = at24_probe,
 604         .remove = __devexit_p(at24_remove),
 605         .id_table = at24_ids,
 606 };
 607
 608 static int __init at24_init(void)
 609 {
 610         io_limit = rounddown_pow_of_two(io_limit);
 611         return i2c_add_driver(&at24_driver);
 612 }
 613 module_init(at24_init);
 614
 615 static void __exit at24_exit(void)
 616 {
 617         i2c_del_driver(&at24_driver);
 618 }
 619 module_exit(at24_exit);
 620
 621 MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
 622 MODULE_AUTHOR("David Brownell and Wolfram Sang");
 623 MODULE_LICENSE("GPL");