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         bool use_smbus;
  57
  58         /*
  59          * Lock protects against activities from other Linux tasks,
  60          * but not from changes by other I2C masters.
  61          */
  62         struct mutex lock;
  63         struct bin_attribute bin;
  64
  65         u8 *writebuf;
  66         unsigned write_max;
  67         unsigned num_addresses;
  68
  69         /*
  70          * Some chips tie up multiple I2C addresses; dummy devices reserve
  71          * them for us, and we'll use them with SMBus calls.
  72          */
  73         struct i2c_client *client[];
  74 };
  75
  76 /*
  77  * This parameter is to help this driver avoid blocking other drivers out
  78  * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
  79  * clock, one 256 byte read takes about 1/43 second which is excessive;
  80  * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
  81  * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
  82  *
  83  * This value is forced to be a power of two so that writes align on pages.
  84  */
  85 static unsigned io_limit = 128;
  86 module_param(io_limit, uint, 0);
  87 MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");
  88
  89 /*
  90  * Specs often allow 5 msec for a page write, sometimes 20 msec;
  91  * it's important to recover from write timeouts.
  92  */
  93 static unsigned write_timeout = 25;
  94 module_param(write_timeout, uint, 0);
  95 MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
  96
  97 #define AT24_SIZE_BYTELEN 5
  98 #define AT24_SIZE_FLAGS 8
  99
 100 #define AT24_BITMASK(x) (BIT(x) - 1)
 101
 102 /* create non-zero magic value for given eeprom parameters */
 103 #define AT24_DEVICE_MAGIC(_len, _flags)                 \
 104         ((1 << AT24_SIZE_FLAGS | (_flags))              \
 105             << AT24_SIZE_BYTELEN | ilog2(_len))
 106
 107 static const struct i2c_device_id at24_ids[] = {
 108         /* needs 8 addresses as A0-A2 are ignored */
 109         { "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },
 110         /* old variants can't be handled with this generic entry! */
 111         { "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
 112         { "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
 113         /* spd is a 24c02 in memory DIMMs */
 114         { "spd", AT24_DEVICE_MAGIC(2048 / 8,
 115                 AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
 116         { "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },
 117         /* 24rf08 quirk is handled at i2c-core */
 118         { "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },
 119         { "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },
 120         { "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },
 121         { "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },
 122         { "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },
 123         { "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },
 124         { "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },
 125         { "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },
 126         { "at24", 0 },
 127         { /* END OF LIST */ }
 128 };
 129 MODULE_DEVICE_TABLE(i2c, at24_ids);
 130
 131 /*-------------------------------------------------------------------------*/
 132
 133 /*
 134  * This routine supports chips which consume multiple I2C addresses. It
 135  * computes the addressing information to be used for a given r/w request.
 136  * Assumes that sanity checks for offset happened at sysfs-layer.
 137  */
 138 static struct i2c_client *at24_translate_offset(struct at24_data *at24,
 139                 unsigned *offset)
 140 {
 141         unsigned i;
 142
 143         if (at24->chip.flags & AT24_FLAG_ADDR16) {
 144                 i = *offset >> 16;
 145                 *offset &= 0xffff;
 146         } else {
 147                 i = *offset >> 8;
 148                 *offset &= 0xff;
 149         }
 150
 151         return at24->client[i];
 152 }
 153
 154 static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
 155                 unsigned offset, size_t count)
 156 {
 157         struct i2c_msg msg[2];
 158         u8 msgbuf[2];
 159         struct i2c_client *client;
 160         int status, i;
 161
 162         memset(msg, 0, sizeof(msg));
 163
 164         /*
 165          * REVISIT some multi-address chips don't rollover page reads to
 166          * the next slave address, so we may need to truncate the count.
 167          * Those chips might need another quirk flag.
 168          *
 169          * If the real hardware used four adjacent 24c02 chips and that
 170          * were misconfigured as one 24c08, that would be a similar effect:
 171          * one "eeprom" file not four, but larger reads would fail when
 172          * they crossed certain pages.
 173          */
 174
 175         /*
 176          * Slave address and byte offset derive from the offset. Always
 177          * set the byte address; on a multi-master board, another master
 178          * may have changed the chip's "current" address pointer.
 179          */
 180         client = at24_translate_offset(at24, &offset);
 181
 182         if (count > io_limit)
 183                 count = io_limit;
 184
 185         /* Smaller eeproms can work given some SMBus extension calls */
 186         if (at24->use_smbus) {
 187                 if (count > I2C_SMBUS_BLOCK_MAX)
 188                         count = I2C_SMBUS_BLOCK_MAX;
 189                 status = i2c_smbus_read_i2c_block_data(client, offset,
 190                                 count, buf);
 191                 dev_dbg(&client->dev, "smbus read %zu@%d --> %d\n",
 192                                 count, offset, status);
 193                 return (status < 0) ? -EIO : status;
 194         }
 195
 196         /*
 197          * When we have a better choice than SMBus calls, use a combined
 198          * I2C message. Write address; then read up to io_limit data bytes.
 199          * Note that read page rollover helps us here (unlike writes).
 200          * msgbuf is u8 and will cast to our needs.
 201          */
 202         i = 0;
 203         if (at24->chip.flags & AT24_FLAG_ADDR16)
 204                 msgbuf[i++] = offset >> 8;
 205         msgbuf[i++] = offset;
 206
 207         msg[0].addr = client->addr;
 208         msg[0].buf = msgbuf;
 209         msg[0].len = i;
 210
 211         msg[1].addr = client->addr;
 212         msg[1].flags = I2C_M_RD;
 213         msg[1].buf = buf;
 214         msg[1].len = count;
 215
 216         status = i2c_transfer(client->adapter, msg, 2);
 217         dev_dbg(&client->dev, "i2c read %zu@%d --> %d\n",
 218                         count, offset, status);
 219
 220         if (status == 2)
 221                 return count;
 222         else if (status >= 0)
 223                 return -EIO;
 224         else
 225                 return status;
 226 }
 227
 228 static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
 229                 char *buf, loff_t off, size_t count)
 230 {
 231         struct at24_data *at24;
 232         ssize_t retval = 0;
 233
 234         at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 235
 236         if (unlikely(!count))
 237                 return count;
 238
 239         /*
 240          * Read data from chip, protecting against concurrent updates
 241          * from this host, but not from other I2C masters.
 242          */
 243         mutex_lock(&at24->lock);
 244
 245         while (count) {
 246                 ssize_t status;
 247
 248                 status = at24_eeprom_read(at24, buf, off, count);
 249                 if (status <= 0) {
 250                         if (retval == 0)
 251                                 retval = status;
 252                         break;
 253                 }
 254                 buf += status;
 255                 off += status;
 256                 count -= status;
 257                 retval += status;
 258         }
 259
 260         mutex_unlock(&at24->lock);
 261
 262         return retval;
 263 }
 264
 265
 266 /*
 267  * REVISIT: export at24_bin{read,write}() to let other kernel code use
 268  * eeprom data. For example, it might hold a board's Ethernet address, or
 269  * board-specific calibration data generated on the manufacturing floor.
 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_bin_write(struct kobject *kobj, struct bin_attribute *attr,
 351                 char *buf, loff_t off, size_t count)
 352 {
 353         struct at24_data *at24;
 354         ssize_t retval = 0;
 355
 356         at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
 357
 358         if (unlikely(!count))
 359                 return count;
 360
 361         /*
 362          * Write data to chip, protecting against concurrent updates
 363          * from this host, but not from other I2C masters.
 364          */
 365         mutex_lock(&at24->lock);
 366
 367         while (count) {
 368                 ssize_t status;
 369
 370                 status = at24_eeprom_write(at24, buf, off, count);
 371                 if (status <= 0) {
 372                         if (retval == 0)
 373                                 retval = status;
 374                         break;
 375                 }
 376                 buf += status;
 377                 off += status;
 378                 count -= status;
 379                 retval += status;
 380         }
 381
 382         mutex_unlock(&at24->lock);
 383
 384         return retval;
 385 }
 386
 387 /*-------------------------------------------------------------------------*/
 388
 389 static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
 390 {
 391         struct at24_platform_data chip;
 392         bool writable;
 393         bool use_smbus = false;
 394         struct at24_data *at24;
 395         int err;
 396         unsigned i, num_addresses;
 397         kernel_ulong_t magic;
 398
 399         if (client->dev.platform_data) {
 400                 chip = *(struct at24_platform_data *)client->dev.platform_data;
 401         } else {
 402                 if (!id->driver_data) {
 403                         err = -ENODEV;
 404                         goto err_out;
 405                 }
 406                 magic = id->driver_data;
 407                 chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
 408                 magic >>= AT24_SIZE_BYTELEN;
 409                 chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
 410                 /*
 411                  * This is slow, but we can't know all eeproms, so we better
 412                  * play safe. Specifying custom eeprom-types via platform_data
 413                  * is recommended anyhow.
 414                  */
 415                 chip.page_size = 1;
 416         }
 417
 418         if (!is_power_of_2(chip.byte_len))
 419                 dev_warn(&client->dev,
 420                         "byte_len looks suspicious (no power of 2)!\n");
 421         if (!is_power_of_2(chip.page_size))
 422                 dev_warn(&client->dev,
 423                         "page_size looks suspicious (no power of 2)!\n");
 424
 425         /* Use I2C operations unless we're stuck with SMBus extensions. */
 426         if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
 427                 if (chip.flags & AT24_FLAG_ADDR16) {
 428                         err = -EPFNOSUPPORT;
 429                         goto err_out;
 430                 }
 431                 if (!i2c_check_functionality(client->adapter,
 432                                 I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 433                         err = -EPFNOSUPPORT;
 434                         goto err_out;
 435                 }
 436                 use_smbus = true;
 437         }
 438
 439         if (chip.flags & AT24_FLAG_TAKE8ADDR)
 440                 num_addresses = 8;
 441         else
 442                 num_addresses = DIV_ROUND_UP(chip.byte_len,
 443                         (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
 444
 445         at24 = kzalloc(sizeof(struct at24_data) +
 446                 num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
 447         if (!at24) {
 448                 err = -ENOMEM;
 449                 goto err_out;
 450         }
 451
 452         mutex_init(&at24->lock);
 453         at24->use_smbus = use_smbus;
 454         at24->chip = chip;
 455         at24->num_addresses = num_addresses;
 456
 457         /*
 458          * Export the EEPROM bytes through sysfs, since that's convenient.
 459          * By default, only root should see the data (maybe passwords etc)
 460          */
 461         at24->bin.attr.name = "eeprom";
 462         at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
 463         at24->bin.read = at24_bin_read;
 464         at24->bin.size = chip.byte_len;
 465
 466         writable = !(chip.flags & AT24_FLAG_READONLY);
 467         if (writable) {
 468                 if (!use_smbus || i2c_check_functionality(client->adapter,
 469                                 I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
 470
 471                         unsigned write_max = chip.page_size;
 472
 473                         at24->bin.write = at24_bin_write;
 474                         at24->bin.attr.mode |= S_IWUSR;
 475
 476                         if (write_max > io_limit)
 477                                 write_max = io_limit;
 478                         if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
 479                                 write_max = I2C_SMBUS_BLOCK_MAX;
 480                         at24->write_max = write_max;
 481
 482                         /* buffer (data + address at the beginning) */
 483                         at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
 484                         if (!at24->writebuf) {
 485                                 err = -ENOMEM;
 486                                 goto err_struct;
 487                         }
 488                 } else {
 489                         dev_warn(&client->dev,
 490                                 "cannot write due to controller restrictions.");
 491                 }
 492         }
 493
 494         at24->client[0] = client;
 495
 496         /* use dummy devices for multiple-address chips */
 497         for (i = 1; i < num_addresses; i++) {
 498                 at24->client[i] = i2c_new_dummy(client->adapter,
 499                                         client->addr + i);
 500                 if (!at24->client[i]) {
 501                         dev_err(&client->dev, "address 0x%02x unavailable\n",
 502                                         client->addr + i);
 503                         err = -EADDRINUSE;
 504                         goto err_clients;
 505                 }
 506         }
 507
 508         err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
 509         if (err)
 510                 goto err_clients;
 511
 512         i2c_set_clientdata(client, at24);
 513
 514         dev_info(&client->dev, "%zu byte %s EEPROM %s\n",
 515                 at24->bin.size, client->name,
 516                 writable ? "(writable)" : "(read-only)");
 517         dev_dbg(&client->dev,
 518                 "page_size %d, num_addresses %d, write_max %d%s\n",
 519                 chip.page_size, num_addresses,
 520                 at24->write_max,
 521                 use_smbus ? ", use_smbus" : "");
 522
 523         return 0;
 524
 525 err_clients:
 526         for (i = 1; i < num_addresses; i++)
 527                 if (at24->client[i])
 528                         i2c_unregister_device(at24->client[i]);
 529
 530         kfree(at24->writebuf);
 531 err_struct:
 532         kfree(at24);
 533 err_out:
 534         dev_dbg(&client->dev, "probe error %d\n", err);
 535         return err;
 536 }
 537
 538 static int __devexit at24_remove(struct i2c_client *client)
 539 {
 540         struct at24_data *at24;
 541         int i;
 542
 543         at24 = i2c_get_clientdata(client);
 544         sysfs_remove_bin_file(&client->dev.kobj, &at24->bin);
 545
 546         for (i = 1; i < at24->num_addresses; i++)
 547                 i2c_unregister_device(at24->client[i]);
 548
 549         kfree(at24->writebuf);
 550         kfree(at24);
 551         i2c_set_clientdata(client, NULL);
 552         return 0;
 553 }
 554
 555 /*-------------------------------------------------------------------------*/
 556
 557 static struct i2c_driver at24_driver = {
 558         .driver = {
 559                 .name = "at24",
 560                 .owner = THIS_MODULE,
 561         },
 562         .probe = at24_probe,
 563         .remove = __devexit_p(at24_remove),
 564         .id_table = at24_ids,
 565 };
 566
 567 static int __init at24_init(void)
 568 {
 569         io_limit = rounddown_pow_of_two(io_limit);
 570         return i2c_add_driver(&at24_driver);
 571 }
 572 module_init(at24_init);
 573
 574 static void __exit at24_exit(void)
 575 {
 576         i2c_del_driver(&at24_driver);
 577 }
 578 module_exit(at24_exit);
 579
 580 MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
 581 MODULE_AUTHOR("David Brownell and Wolfram Sang");
 582 MODULE_LICENSE("GPL");