drivers/mtd/nand/nand_ecc.c

   1 /*
   2  * This file contains an ECC algorithm that detects and corrects 1 bit
   3  * errors in a 256 byte block of data.
   4  *
   5  * drivers/mtd/nand/nand_ecc.c
   6  *
   7  * Copyright © 2008 Koninklijke Philips Electronics NV.
   8  *                  Author: Frans Meulenbroeks
   9  *
  10  * Completely replaces the previous ECC implementation which was written by:
  11  *   Steven J. Hill (sjhill@realitydiluted.com)
  12  *   Thomas Gleixner (tglx@linutronix.de)
  13  *
  14  * Information on how this algorithm works and how it was developed
  15  * can be found in Documentation/mtd/nand_ecc.txt
  16  *
  17  * This file is free software; you can redistribute it and/or modify it
  18  * under the terms of the GNU General Public License as published by the
  19  * Free Software Foundation; either version 2 or (at your option) any
  20  * later version.
  21  *
  22  * This file is distributed in the hope that it will be useful, but WITHOUT
  23  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  24  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  25  * for more details.
  26  *
  27  * You should have received a copy of the GNU General Public License along
  28  * with this file; if not, write to the Free Software Foundation, Inc.,
  29  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  30  *
  31  */
  32
  33 /*
  34  * The STANDALONE macro is useful when running the code outside the kernel
  35  * e.g. when running the code in a testbed or a benchmark program.
  36  * When STANDALONE is used, the module related macros are commented out
  37  * as well as the linux include files.
  38  * Instead a private definition of mtd_info is given to satisfy the compiler
  39  * (the code does not use mtd_info, so the code does not care)
  40  */
  41 #ifndef STANDALONE
  42 #include <linux/types.h>
  43 #include <linux/kernel.h>
  44 #include <linux/module.h>
  45 #include <linux/mtd/mtd.h>
  46 #include <linux/mtd/nand.h>
  47 #include <linux/mtd/nand_ecc.h>
  48 #include <asm/byteorder.h>
  49 #else
  50 #include <stdint.h>
  51 struct mtd_info;
  52 #define EXPORT_SYMBOL(x)  /* x */
  53
  54 #define MODULE_LICENSE(x)       /* x */
  55 #define MODULE_AUTHOR(x)        /* x */
  56 #define MODULE_DESCRIPTION(x)   /* x */
  57
  58 #define printk printf
  59 #define KERN_ERR                ""
  60 #endif
  61
  62 /*
  63  * invparity is a 256 byte table that contains the odd parity
  64  * for each byte. So if the number of bits in a byte is even,
  65  * the array element is 1, and when the number of bits is odd
  66  * the array eleemnt is 0.
  67  */
  68 static const char invparity[256] = {
  69         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  70         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  71         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  72         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  73         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  74         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  75         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  76         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  77         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  78         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  79         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  80         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  81         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
  82         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  83         0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
  84         1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1
  85 };
  86
  87 /*
  88  * bitsperbyte contains the number of bits per byte
  89  * this is only used for testing and repairing parity
  90  * (a precalculated value slightly improves performance)
  91  */
  92 static const char bitsperbyte[256] = {
  93         0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
  94         1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
  95         1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
  96         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
  97         1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
  98         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
  99         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
 100         3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
 101         1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
 102         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
 103         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
 104         3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
 105         2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
 106         3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
 107         3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
 108         4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
 109 };
 110
 111 /*
 112  * addressbits is a lookup table to filter out the bits from the xor-ed
 113  * ecc data that identify the faulty location.
 114  * this is only used for repairing parity
 115  * see the comments in nand_correct_data for more details
 116  */
 117 static const char addressbits[256] = {
 118         0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
 119         0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
 120         0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
 121         0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
 122         0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
 123         0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
 124         0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
 125         0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
 126         0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
 127         0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
 128         0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
 129         0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
 130         0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
 131         0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
 132         0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
 133         0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
 134         0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
 135         0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
 136         0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
 137         0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
 138         0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
 139         0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
 140         0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
 141         0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
 142         0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
 143         0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
 144         0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
 145         0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
 146         0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
 147         0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
 148         0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
 149         0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f
 150 };
 151
 152 /**
 153  * nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
 154  *                       block
 155  * @mtd:        MTD block structure
 156  * @buf:        input buffer with raw data
 157  * @code:       output buffer with ECC
 158  */
 159 int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
 160                        unsigned char *code)
 161 {
 162         int i;
 163         const uint32_t *bp = (uint32_t *)buf;
 164         /* 256 or 512 bytes/ecc  */
 165         const uint32_t eccsize_mult =
 166                         (((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
 167         uint32_t cur;           /* current value in buffer */
 168         /* rp0..rp15..rp17 are the various accumulated parities (per byte) */
 169         uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
 170         uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
 171         uint32_t uninitialized_var(rp17);       /* to make compiler happy */
 172         uint32_t par;           /* the cumulative parity for all data */
 173         uint32_t tmppar;        /* the cumulative parity for this iteration;
 174                                    for rp12, rp14 and rp16 at the end of the
 175                                    loop */
 176
 177         par = 0;
 178         rp4 = 0;
 179         rp6 = 0;
 180         rp8 = 0;
 181         rp10 = 0;
 182         rp12 = 0;
 183         rp14 = 0;
 184         rp16 = 0;
 185
 186         /*
 187          * The loop is unrolled a number of times;
 188          * This avoids if statements to decide on which rp value to update
 189          * Also we process the data by longwords.
 190          * Note: passing unaligned data might give a performance penalty.
 191          * It is assumed that the buffers are aligned.
 192          * tmppar is the cumulative sum of this iteration.
 193          * needed for calculating rp12, rp14, rp16 and par
 194          * also used as a performance improvement for rp6, rp8 and rp10
 195          */
 196         for (i = 0; i < eccsize_mult << 2; i++) {
 197                 cur = *bp++;
 198                 tmppar = cur;
 199                 rp4 ^= cur;
 200                 cur = *bp++;
 201                 tmppar ^= cur;
 202                 rp6 ^= tmppar;
 203                 cur = *bp++;
 204                 tmppar ^= cur;
 205                 rp4 ^= cur;
 206                 cur = *bp++;
 207                 tmppar ^= cur;
 208                 rp8 ^= tmppar;
 209
 210                 cur = *bp++;
 211                 tmppar ^= cur;
 212                 rp4 ^= cur;
 213                 rp6 ^= cur;
 214                 cur = *bp++;
 215                 tmppar ^= cur;
 216                 rp6 ^= cur;
 217                 cur = *bp++;
 218                 tmppar ^= cur;
 219                 rp4 ^= cur;
 220                 cur = *bp++;
 221                 tmppar ^= cur;
 222                 rp10 ^= tmppar;
 223
 224                 cur = *bp++;
 225                 tmppar ^= cur;
 226                 rp4 ^= cur;
 227                 rp6 ^= cur;
 228                 rp8 ^= cur;
 229                 cur = *bp++;
 230                 tmppar ^= cur;
 231                 rp6 ^= cur;
 232                 rp8 ^= cur;
 233                 cur = *bp++;
 234                 tmppar ^= cur;
 235                 rp4 ^= cur;
 236                 rp8 ^= cur;
 237                 cur = *bp++;
 238                 tmppar ^= cur;
 239                 rp8 ^= cur;
 240
 241                 cur = *bp++;
 242                 tmppar ^= cur;
 243                 rp4 ^= cur;
 244                 rp6 ^= cur;
 245                 cur = *bp++;
 246                 tmppar ^= cur;
 247                 rp6 ^= cur;
 248                 cur = *bp++;
 249                 tmppar ^= cur;
 250                 rp4 ^= cur;
 251                 cur = *bp++;
 252                 tmppar ^= cur;
 253
 254                 par ^= tmppar;
 255                 if ((i & 0x1) == 0)
 256                         rp12 ^= tmppar;
 257                 if ((i & 0x2) == 0)
 258                         rp14 ^= tmppar;
 259                 if (eccsize_mult == 2 && (i & 0x4) == 0)
 260                         rp16 ^= tmppar;
 261         }
 262
 263         /*
 264          * handle the fact that we use longword operations
 265          * we'll bring rp4..rp14..rp16 back to single byte entities by
 266          * shifting and xoring first fold the upper and lower 16 bits,
 267          * then the upper and lower 8 bits.
 268          */
 269         rp4 ^= (rp4 >> 16);
 270         rp4 ^= (rp4 >> 8);
 271         rp4 &= 0xff;
 272         rp6 ^= (rp6 >> 16);
 273         rp6 ^= (rp6 >> 8);
 274         rp6 &= 0xff;
 275         rp8 ^= (rp8 >> 16);
 276         rp8 ^= (rp8 >> 8);
 277         rp8 &= 0xff;
 278         rp10 ^= (rp10 >> 16);
 279         rp10 ^= (rp10 >> 8);
 280         rp10 &= 0xff;
 281         rp12 ^= (rp12 >> 16);
 282         rp12 ^= (rp12 >> 8);
 283         rp12 &= 0xff;
 284         rp14 ^= (rp14 >> 16);
 285         rp14 ^= (rp14 >> 8);
 286         rp14 &= 0xff;
 287         if (eccsize_mult == 2) {
 288                 rp16 ^= (rp16 >> 16);
 289                 rp16 ^= (rp16 >> 8);
 290                 rp16 &= 0xff;
 291         }
 292
 293         /*
 294          * we also need to calculate the row parity for rp0..rp3
 295          * This is present in par, because par is now
 296          * rp3 rp3 rp2 rp2 in little endian and
 297          * rp2 rp2 rp3 rp3 in big endian
 298          * as well as
 299          * rp1 rp0 rp1 rp0 in little endian and
 300          * rp0 rp1 rp0 rp1 in big endian
 301          * First calculate rp2 and rp3
 302          */
 303 #ifdef __BIG_ENDIAN
 304         rp2 = (par >> 16);
 305         rp2 ^= (rp2 >> 8);
 306         rp2 &= 0xff;
 307         rp3 = par & 0xffff;
 308         rp3 ^= (rp3 >> 8);
 309         rp3 &= 0xff;
 310 #else
 311         rp3 = (par >> 16);
 312         rp3 ^= (rp3 >> 8);
 313         rp3 &= 0xff;
 314         rp2 = par & 0xffff;
 315         rp2 ^= (rp2 >> 8);
 316         rp2 &= 0xff;
 317 #endif
 318
 319         /* reduce par to 16 bits then calculate rp1 and rp0 */
 320         par ^= (par >> 16);
 321 #ifdef __BIG_ENDIAN
 322         rp0 = (par >> 8) & 0xff;
 323         rp1 = (par & 0xff);
 324 #else
 325         rp1 = (par >> 8) & 0xff;
 326         rp0 = (par & 0xff);
 327 #endif
 328
 329         /* finally reduce par to 8 bits */
 330         par ^= (par >> 8);
 331         par &= 0xff;
 332
 333         /*
 334          * and calculate rp5..rp15..rp17
 335          * note that par = rp4 ^ rp5 and due to the commutative property
 336          * of the ^ operator we can say:
 337          * rp5 = (par ^ rp4);
 338          * The & 0xff seems superfluous, but benchmarking learned that
 339          * leaving it out gives slightly worse results. No idea why, probably
 340          * it has to do with the way the pipeline in pentium is organized.
 341          */
 342         rp5 = (par ^ rp4) & 0xff;
 343         rp7 = (par ^ rp6) & 0xff;
 344         rp9 = (par ^ rp8) & 0xff;
 345         rp11 = (par ^ rp10) & 0xff;
 346         rp13 = (par ^ rp12) & 0xff;
 347         rp15 = (par ^ rp14) & 0xff;
 348         if (eccsize_mult == 2)
 349                 rp17 = (par ^ rp16) & 0xff;
 350
 351         /*
 352          * Finally calculate the ecc bits.
 353          * Again here it might seem that there are performance optimisations
 354          * possible, but benchmarks showed that on the system this is developed
 355          * the code below is the fastest
 356          */
 357 #ifdef CONFIG_MTD_NAND_ECC_SMC
 358         code[0] =
 359             (invparity[rp7] << 7) |
 360             (invparity[rp6] << 6) |
 361             (invparity[rp5] << 5) |
 362             (invparity[rp4] << 4) |
 363             (invparity[rp3] << 3) |
 364             (invparity[rp2] << 2) |
 365             (invparity[rp1] << 1) |
 366             (invparity[rp0]);
 367         code[1] =
 368             (invparity[rp15] << 7) |
 369             (invparity[rp14] << 6) |
 370             (invparity[rp13] << 5) |
 371             (invparity[rp12] << 4) |
 372             (invparity[rp11] << 3) |
 373             (invparity[rp10] << 2) |
 374             (invparity[rp9] << 1)  |
 375             (invparity[rp8]);
 376 #else
 377         code[1] =
 378             (invparity[rp7] << 7) |
 379             (invparity[rp6] << 6) |
 380             (invparity[rp5] << 5) |
 381             (invparity[rp4] << 4) |
 382             (invparity[rp3] << 3) |
 383             (invparity[rp2] << 2) |
 384             (invparity[rp1] << 1) |
 385             (invparity[rp0]);
 386         code[0] =
 387             (invparity[rp15] << 7) |
 388             (invparity[rp14] << 6) |
 389             (invparity[rp13] << 5) |
 390             (invparity[rp12] << 4) |
 391             (invparity[rp11] << 3) |
 392             (invparity[rp10] << 2) |
 393             (invparity[rp9] << 1)  |
 394             (invparity[rp8]);
 395 #endif
 396         if (eccsize_mult == 1)
 397                 code[2] =
 398                     (invparity[par & 0xf0] << 7) |
 399                     (invparity[par & 0x0f] << 6) |
 400                     (invparity[par & 0xcc] << 5) |
 401                     (invparity[par & 0x33] << 4) |
 402                     (invparity[par & 0xaa] << 3) |
 403                     (invparity[par & 0x55] << 2) |
 404                     3;
 405         else
 406                 code[2] =
 407                     (invparity[par & 0xf0] << 7) |
 408                     (invparity[par & 0x0f] << 6) |
 409                     (invparity[par & 0xcc] << 5) |
 410                     (invparity[par & 0x33] << 4) |
 411                     (invparity[par & 0xaa] << 3) |
 412                     (invparity[par & 0x55] << 2) |
 413                     (invparity[rp17] << 1) |
 414                     (invparity[rp16] << 0);
 415         return 0;
 416 }
 417 EXPORT_SYMBOL(nand_calculate_ecc);
 418
 419 /**
 420  * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 421  * @mtd:        MTD block structure
 422  * @buf:        raw data read from the chip
 423  * @read_ecc:   ECC from the chip
 424  * @calc_ecc:   the ECC calculated from raw data
 425  *
 426  * Detect and correct a 1 bit error for 256/512 byte block
 427  */
 428 int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
 429                       unsigned char *read_ecc, unsigned char *calc_ecc)
 430 {
 431         unsigned char b0, b1, b2, bit_addr;
 432         unsigned int byte_addr;
 433         /* 256 or 512 bytes/ecc  */
 434         const uint32_t eccsize_mult =
 435                         (((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
 436
 437         /*
 438          * b0 to b2 indicate which bit is faulty (if any)
 439          * we might need the xor result  more than once,
 440          * so keep them in a local var
 441         */
 442 #ifdef CONFIG_MTD_NAND_ECC_SMC
 443         b0 = read_ecc[0] ^ calc_ecc[0];
 444         b1 = read_ecc[1] ^ calc_ecc[1];
 445 #else
 446         b0 = read_ecc[1] ^ calc_ecc[1];
 447         b1 = read_ecc[0] ^ calc_ecc[0];
 448 #endif
 449         b2 = read_ecc[2] ^ calc_ecc[2];
 450
 451         /* check if there are any bitfaults */
 452
 453         /* repeated if statements are slightly more efficient than switch ... */
 454         /* ordered in order of likelihood */
 455
 456         if ((b0 | b1 | b2) == 0)
 457                 return 0;       /* no error */
 458
 459         if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
 460             (((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
 461             ((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
 462              (eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
 463         /* single bit error */
 464                 /*
 465                  * rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
 466                  * byte, cp 5/3/1 indicate the faulty bit.
 467                  * A lookup table (called addressbits) is used to filter
 468                  * the bits from the byte they are in.
 469                  * A marginal optimisation is possible by having three
 470                  * different lookup tables.
 471                  * One as we have now (for b0), one for b2
 472                  * (that would avoid the >> 1), and one for b1 (with all values
 473                  * << 4). However it was felt that introducing two more tables
 474                  * hardly justify the gain.
 475                  *
 476                  * The b2 shift is there to get rid of the lowest two bits.
 477                  * We could also do addressbits[b2] >> 1 but for the
 478                  * performace it does not make any difference
 479                  */
 480                 if (eccsize_mult == 1)
 481                         byte_addr = (addressbits[b1] << 4) + addressbits[b0];
 482                 else
 483                         byte_addr = (addressbits[b2 & 0x3] << 8) +
 484                                     (addressbits[b1] << 4) + addressbits[b0];
 485                 bit_addr = addressbits[b2 >> 2];
 486                 /* flip the bit */
 487                 buf[byte_addr] ^= (1 << bit_addr);
 488                 return 1;
 489
 490         }
 491         /* count nr of bits; use table lookup, faster than calculating it */
 492         if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
 493                 return 1;       /* error in ecc data; no action needed */
 494
 495         printk(KERN_ERR "uncorrectable error : ");
 496         return -1;
 497 }
 498 EXPORT_SYMBOL(nand_correct_data);
 499
 500 MODULE_LICENSE("GPL");
 501 MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
 502 MODULE_DESCRIPTION("Generic NAND ECC support");