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  * @buf:        input buffer with raw data
 156  * @eccsize:    data bytes per ECC step (256 or 512)
 157  * @code:       output buffer with ECC
 158  */
 159 void __nand_calculate_ecc(const unsigned char *buf, unsigned int eccsize,
 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 = eccsize >> 8;
 166         uint32_t cur;           /* current value in buffer */
 167         /* rp0..rp15..rp17 are the various accumulated parities (per byte) */
 168         uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
 169         uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
 170         uint32_t uninitialized_var(rp17);       /* to make compiler happy */
 171         uint32_t par;           /* the cumulative parity for all data */
 172         uint32_t tmppar;        /* the cumulative parity for this iteration;
 173                                    for rp12, rp14 and rp16 at the end of the
 174                                    loop */
 175
 176         par = 0;
 177         rp4 = 0;
 178         rp6 = 0;
 179         rp8 = 0;
 180         rp10 = 0;
 181         rp12 = 0;
 182         rp14 = 0;
 183         rp16 = 0;
 184
 185         /*
 186          * The loop is unrolled a number of times;
 187          * This avoids if statements to decide on which rp value to update
 188          * Also we process the data by longwords.
 189          * Note: passing unaligned data might give a performance penalty.
 190          * It is assumed that the buffers are aligned.
 191          * tmppar is the cumulative sum of this iteration.
 192          * needed for calculating rp12, rp14, rp16 and par
 193          * also used as a performance improvement for rp6, rp8 and rp10
 194          */
 195         for (i = 0; i < eccsize_mult << 2; i++) {
 196                 cur = *bp++;
 197                 tmppar = cur;
 198                 rp4 ^= cur;
 199                 cur = *bp++;
 200                 tmppar ^= cur;
 201                 rp6 ^= tmppar;
 202                 cur = *bp++;
 203                 tmppar ^= cur;
 204                 rp4 ^= cur;
 205                 cur = *bp++;
 206                 tmppar ^= cur;
 207                 rp8 ^= tmppar;
 208
 209                 cur = *bp++;
 210                 tmppar ^= cur;
 211                 rp4 ^= cur;
 212                 rp6 ^= cur;
 213                 cur = *bp++;
 214                 tmppar ^= cur;
 215                 rp6 ^= cur;
 216                 cur = *bp++;
 217                 tmppar ^= cur;
 218                 rp4 ^= cur;
 219                 cur = *bp++;
 220                 tmppar ^= cur;
 221                 rp10 ^= tmppar;
 222
 223                 cur = *bp++;
 224                 tmppar ^= cur;
 225                 rp4 ^= cur;
 226                 rp6 ^= cur;
 227                 rp8 ^= cur;
 228                 cur = *bp++;
 229                 tmppar ^= cur;
 230                 rp6 ^= cur;
 231                 rp8 ^= cur;
 232                 cur = *bp++;
 233                 tmppar ^= cur;
 234                 rp4 ^= cur;
 235                 rp8 ^= cur;
 236                 cur = *bp++;
 237                 tmppar ^= cur;
 238                 rp8 ^= cur;
 239
 240                 cur = *bp++;
 241                 tmppar ^= cur;
 242                 rp4 ^= cur;
 243                 rp6 ^= cur;
 244                 cur = *bp++;
 245                 tmppar ^= cur;
 246                 rp6 ^= cur;
 247                 cur = *bp++;
 248                 tmppar ^= cur;
 249                 rp4 ^= cur;
 250                 cur = *bp++;
 251                 tmppar ^= cur;
 252
 253                 par ^= tmppar;
 254                 if ((i & 0x1) == 0)
 255                         rp12 ^= tmppar;
 256                 if ((i & 0x2) == 0)
 257                         rp14 ^= tmppar;
 258                 if (eccsize_mult == 2 && (i & 0x4) == 0)
 259                         rp16 ^= tmppar;
 260         }
 261
 262         /*
 263          * handle the fact that we use longword operations
 264          * we'll bring rp4..rp14..rp16 back to single byte entities by
 265          * shifting and xoring first fold the upper and lower 16 bits,
 266          * then the upper and lower 8 bits.
 267          */
 268         rp4 ^= (rp4 >> 16);
 269         rp4 ^= (rp4 >> 8);
 270         rp4 &= 0xff;
 271         rp6 ^= (rp6 >> 16);
 272         rp6 ^= (rp6 >> 8);
 273         rp6 &= 0xff;
 274         rp8 ^= (rp8 >> 16);
 275         rp8 ^= (rp8 >> 8);
 276         rp8 &= 0xff;
 277         rp10 ^= (rp10 >> 16);
 278         rp10 ^= (rp10 >> 8);
 279         rp10 &= 0xff;
 280         rp12 ^= (rp12 >> 16);
 281         rp12 ^= (rp12 >> 8);
 282         rp12 &= 0xff;
 283         rp14 ^= (rp14 >> 16);
 284         rp14 ^= (rp14 >> 8);
 285         rp14 &= 0xff;
 286         if (eccsize_mult == 2) {
 287                 rp16 ^= (rp16 >> 16);
 288                 rp16 ^= (rp16 >> 8);
 289                 rp16 &= 0xff;
 290         }
 291
 292         /*
 293          * we also need to calculate the row parity for rp0..rp3
 294          * This is present in par, because par is now
 295          * rp3 rp3 rp2 rp2 in little endian and
 296          * rp2 rp2 rp3 rp3 in big endian
 297          * as well as
 298          * rp1 rp0 rp1 rp0 in little endian and
 299          * rp0 rp1 rp0 rp1 in big endian
 300          * First calculate rp2 and rp3
 301          */
 302 #ifdef __BIG_ENDIAN
 303         rp2 = (par >> 16);
 304         rp2 ^= (rp2 >> 8);
 305         rp2 &= 0xff;
 306         rp3 = par & 0xffff;
 307         rp3 ^= (rp3 >> 8);
 308         rp3 &= 0xff;
 309 #else
 310         rp3 = (par >> 16);
 311         rp3 ^= (rp3 >> 8);
 312         rp3 &= 0xff;
 313         rp2 = par & 0xffff;
 314         rp2 ^= (rp2 >> 8);
 315         rp2 &= 0xff;
 316 #endif
 317
 318         /* reduce par to 16 bits then calculate rp1 and rp0 */
 319         par ^= (par >> 16);
 320 #ifdef __BIG_ENDIAN
 321         rp0 = (par >> 8) & 0xff;
 322         rp1 = (par & 0xff);
 323 #else
 324         rp1 = (par >> 8) & 0xff;
 325         rp0 = (par & 0xff);
 326 #endif
 327
 328         /* finally reduce par to 8 bits */
 329         par ^= (par >> 8);
 330         par &= 0xff;
 331
 332         /*
 333          * and calculate rp5..rp15..rp17
 334          * note that par = rp4 ^ rp5 and due to the commutative property
 335          * of the ^ operator we can say:
 336          * rp5 = (par ^ rp4);
 337          * The & 0xff seems superfluous, but benchmarking learned that
 338          * leaving it out gives slightly worse results. No idea why, probably
 339          * it has to do with the way the pipeline in pentium is organized.
 340          */
 341         rp5 = (par ^ rp4) & 0xff;
 342         rp7 = (par ^ rp6) & 0xff;
 343         rp9 = (par ^ rp8) & 0xff;
 344         rp11 = (par ^ rp10) & 0xff;
 345         rp13 = (par ^ rp12) & 0xff;
 346         rp15 = (par ^ rp14) & 0xff;
 347         if (eccsize_mult == 2)
 348                 rp17 = (par ^ rp16) & 0xff;
 349
 350         /*
 351          * Finally calculate the ECC bits.
 352          * Again here it might seem that there are performance optimisations
 353          * possible, but benchmarks showed that on the system this is developed
 354          * the code below is the fastest
 355          */
 356 #ifdef CONFIG_MTD_NAND_ECC_SMC
 357         code[0] =
 358             (invparity[rp7] << 7) |
 359             (invparity[rp6] << 6) |
 360             (invparity[rp5] << 5) |
 361             (invparity[rp4] << 4) |
 362             (invparity[rp3] << 3) |
 363             (invparity[rp2] << 2) |
 364             (invparity[rp1] << 1) |
 365             (invparity[rp0]);
 366         code[1] =
 367             (invparity[rp15] << 7) |
 368             (invparity[rp14] << 6) |
 369             (invparity[rp13] << 5) |
 370             (invparity[rp12] << 4) |
 371             (invparity[rp11] << 3) |
 372             (invparity[rp10] << 2) |
 373             (invparity[rp9] << 1)  |
 374             (invparity[rp8]);
 375 #else
 376         code[1] =
 377             (invparity[rp7] << 7) |
 378             (invparity[rp6] << 6) |
 379             (invparity[rp5] << 5) |
 380             (invparity[rp4] << 4) |
 381             (invparity[rp3] << 3) |
 382             (invparity[rp2] << 2) |
 383             (invparity[rp1] << 1) |
 384             (invparity[rp0]);
 385         code[0] =
 386             (invparity[rp15] << 7) |
 387             (invparity[rp14] << 6) |
 388             (invparity[rp13] << 5) |
 389             (invparity[rp12] << 4) |
 390             (invparity[rp11] << 3) |
 391             (invparity[rp10] << 2) |
 392             (invparity[rp9] << 1)  |
 393             (invparity[rp8]);
 394 #endif
 395         if (eccsize_mult == 1)
 396                 code[2] =
 397                     (invparity[par & 0xf0] << 7) |
 398                     (invparity[par & 0x0f] << 6) |
 399                     (invparity[par & 0xcc] << 5) |
 400                     (invparity[par & 0x33] << 4) |
 401                     (invparity[par & 0xaa] << 3) |
 402                     (invparity[par & 0x55] << 2) |
 403                     3;
 404         else
 405                 code[2] =
 406                     (invparity[par & 0xf0] << 7) |
 407                     (invparity[par & 0x0f] << 6) |
 408                     (invparity[par & 0xcc] << 5) |
 409                     (invparity[par & 0x33] << 4) |
 410                     (invparity[par & 0xaa] << 3) |
 411                     (invparity[par & 0x55] << 2) |
 412                     (invparity[rp17] << 1) |
 413                     (invparity[rp16] << 0);
 414 }
 415 EXPORT_SYMBOL(__nand_calculate_ecc);
 416
 417 /**
 418  * nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
 419  *                       block
 420  * @mtd:        MTD block structure
 421  * @buf:        input buffer with raw data
 422  * @code:       output buffer with ECC
 423  */
 424 int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
 425                        unsigned char *code)
 426 {
 427         __nand_calculate_ecc(buf,
 428                         ((struct nand_chip *)mtd->priv)->ecc.size, code);
 429
 430         return 0;
 431 }
 432 EXPORT_SYMBOL(nand_calculate_ecc);
 433
 434 /**
 435  * __nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 436  * @buf:        raw data read from the chip
 437  * @read_ecc:   ECC from the chip
 438  * @calc_ecc:   the ECC calculated from raw data
 439  * @eccsize:    data bytes per ECC step (256 or 512)
 440  *
 441  * Detect and correct a 1 bit error for eccsize byte block
 442  */
 443 int __nand_correct_data(unsigned char *buf,
 444                         unsigned char *read_ecc, unsigned char *calc_ecc,
 445                         unsigned int eccsize)
 446 {
 447         unsigned char b0, b1, b2, bit_addr;
 448         unsigned int byte_addr;
 449         /* 256 or 512 bytes/ecc  */
 450         const uint32_t eccsize_mult = eccsize >> 8;
 451
 452         /*
 453          * b0 to b2 indicate which bit is faulty (if any)
 454          * we might need the xor result  more than once,
 455          * so keep them in a local var
 456         */
 457 #ifdef CONFIG_MTD_NAND_ECC_SMC
 458         b0 = read_ecc[0] ^ calc_ecc[0];
 459         b1 = read_ecc[1] ^ calc_ecc[1];
 460 #else
 461         b0 = read_ecc[1] ^ calc_ecc[1];
 462         b1 = read_ecc[0] ^ calc_ecc[0];
 463 #endif
 464         b2 = read_ecc[2] ^ calc_ecc[2];
 465
 466         /* check if there are any bitfaults */
 467
 468         /* repeated if statements are slightly more efficient than switch ... */
 469         /* ordered in order of likelihood */
 470
 471         if ((b0 | b1 | b2) == 0)
 472                 return 0;       /* no error */
 473
 474         if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
 475             (((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
 476             ((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
 477              (eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
 478         /* single bit error */
 479                 /*
 480                  * rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
 481                  * byte, cp 5/3/1 indicate the faulty bit.
 482                  * A lookup table (called addressbits) is used to filter
 483                  * the bits from the byte they are in.
 484                  * A marginal optimisation is possible by having three
 485                  * different lookup tables.
 486                  * One as we have now (for b0), one for b2
 487                  * (that would avoid the >> 1), and one for b1 (with all values
 488                  * << 4). However it was felt that introducing two more tables
 489                  * hardly justify the gain.
 490                  *
 491                  * The b2 shift is there to get rid of the lowest two bits.
 492                  * We could also do addressbits[b2] >> 1 but for the
 493                  * performance it does not make any difference
 494                  */
 495                 if (eccsize_mult == 1)
 496                         byte_addr = (addressbits[b1] << 4) + addressbits[b0];
 497                 else
 498                         byte_addr = (addressbits[b2 & 0x3] << 8) +
 499                                     (addressbits[b1] << 4) + addressbits[b0];
 500                 bit_addr = addressbits[b2 >> 2];
 501                 /* flip the bit */
 502                 buf[byte_addr] ^= (1 << bit_addr);
 503                 return 1;
 504
 505         }
 506         /* count nr of bits; use table lookup, faster than calculating it */
 507         if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
 508                 return 1;       /* error in ECC data; no action needed */
 509
 510         printk(KERN_ERR "uncorrectable error : ");
 511         return -1;
 512 }
 513 EXPORT_SYMBOL(__nand_correct_data);
 514
 515 /**
 516  * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 517  * @mtd:        MTD block structure
 518  * @buf:        raw data read from the chip
 519  * @read_ecc:   ECC from the chip
 520  * @calc_ecc:   the ECC calculated from raw data
 521  *
 522  * Detect and correct a 1 bit error for 256/512 byte block
 523  */
 524 int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
 525                       unsigned char *read_ecc, unsigned char *calc_ecc)
 526 {
 527         return __nand_correct_data(buf, read_ecc, calc_ecc,
 528                                    ((struct nand_chip *)mtd->priv)->ecc.size);
 529 }
 530 EXPORT_SYMBOL(nand_correct_data);
 531
 532 MODULE_LICENSE("GPL");
 533 MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
 534 MODULE_DESCRIPTION("Generic NAND ECC support");