LXR uboot/fs/yaffs2/yaffs

   1/*
   2 * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
   3 *
   4 * Copyright (C) 2002-2007 Aleph One Ltd.
   5 *   for Toby Churchill Ltd and Brightstar Engineering
   6 *
   7 * Created by Charles Manning <charles@aleph1.co.uk>
   8 *
   9 * This program is free software; you can redistribute it and/or modify
  10 * it under the terms of the GNU General Public License version 2 as
  11 * published by the Free Software Foundation.
  12 */
  13
  14/*
  15 * This code implements the ECC algorithm used in SmartMedia.
  16 *
  17 * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
  18 * The two unused bit are set to 1.
  19 * The ECC can correct single bit errors in a 256-byte page of data. Thus, two such ECC
  20 * blocks are used on a 512-byte NAND page.
  21 *
  22 */
  23
  24/* Table generated by gen-ecc.c
  25 * Using a table means we do not have to calculate p1..p4 and p1'..p4'
  26 * for each byte of data. These are instead provided in a table in bits7..2.
  27 * Bit 0 of each entry indicates whether the entry has an odd or even parity, and therefore
  28 * this bytes influence on the line parity.
  29 */
  30
  31/* XXX U-BOOT XXX */
  32#include <common.h>
  33
  34const char *yaffs_ecc_c_version =
  35    "$Id: yaffs_ecc.c,v 1.9 2007/02/14 01:09:06 wookey Exp $";
  36
  37#include "yportenv.h"
  38
  39#include "yaffs_ecc.h"
  40
  41static const unsigned char column_parity_table[] = {
  42        0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  43        0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  44        0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  45        0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  46        0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  47        0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  48        0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  49        0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  50        0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  51        0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  52        0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  53        0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  54        0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  55        0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  56        0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  57        0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  58        0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  59        0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  60        0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  61        0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  62        0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  63        0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  64        0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  65        0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  66        0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  67        0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  68        0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  69        0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  70        0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  71        0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  72        0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  73        0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  74};
  75
  76/* Count the bits in an unsigned char or a U32 */
  77
  78static int yaffs_CountBits(unsigned char x)
  79{
  80        int r = 0;
  81        while (x) {
  82                if (x & 1)
  83                        r++;
  84                x >>= 1;
  85        }
  86        return r;
  87}
  88
  89static int yaffs_CountBits32(unsigned x)
  90{
  91        int r = 0;
  92        while (x) {
  93                if (x & 1)
  94                        r++;
  95                x >>= 1;
  96        }
  97        return r;
  98}
  99
 100/* Calculate the ECC for a 256-byte block of data */
 101void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
 102{
 103        unsigned int i;
 104
 105        unsigned char col_parity = 0;
 106        unsigned char line_parity = 0;
 107        unsigned char line_parity_prime = 0;
 108        unsigned char t;
 109        unsigned char b;
 110
 111        for (i = 0; i < 256; i++) {
 112                b = column_parity_table[*data++];
 113                col_parity ^= b;
 114
 115                if (b & 0x01)   // odd number of bits in the byte
 116                {
 117                        line_parity ^= i;
 118                        line_parity_prime ^= ~i;
 119                }
 120
 121        }
 122
 123        ecc[2] = (~col_parity) | 0x03;
 124
 125        t = 0;
 126        if (line_parity & 0x80)
 127                t |= 0x80;
 128        if (line_parity_prime & 0x80)
 129                t |= 0x40;
 130        if (line_parity & 0x40)
 131                t |= 0x20;
 132        if (line_parity_prime & 0x40)
 133                t |= 0x10;
 134        if (line_parity & 0x20)
 135                t |= 0x08;
 136        if (line_parity_prime & 0x20)
 137                t |= 0x04;
 138        if (line_parity & 0x10)
 139                t |= 0x02;
 140        if (line_parity_prime & 0x10)
 141                t |= 0x01;
 142        ecc[1] = ~t;
 143
 144        t = 0;
 145        if (line_parity & 0x08)
 146                t |= 0x80;
 147        if (line_parity_prime & 0x08)
 148                t |= 0x40;
 149        if (line_parity & 0x04)
 150                t |= 0x20;
 151        if (line_parity_prime & 0x04)
 152                t |= 0x10;
 153        if (line_parity & 0x02)
 154                t |= 0x08;
 155        if (line_parity_prime & 0x02)
 156                t |= 0x04;
 157        if (line_parity & 0x01)
 158                t |= 0x02;
 159        if (line_parity_prime & 0x01)
 160                t |= 0x01;
 161        ecc[0] = ~t;
 162
 163#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 164        // Swap the bytes into the wrong order
 165        t = ecc[0];
 166        ecc[0] = ecc[1];
 167        ecc[1] = t;
 168#endif
 169}
 170
 171
 172/* Correct the ECC on a 256 byte block of data */
 173
 174int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
 175                     const unsigned char *test_ecc)
 176{
 177        unsigned char d0, d1, d2;       /* deltas */
 178
 179        d0 = read_ecc[0] ^ test_ecc[0];
 180        d1 = read_ecc[1] ^ test_ecc[1];
 181        d2 = read_ecc[2] ^ test_ecc[2];
 182
 183        if ((d0 | d1 | d2) == 0)
 184                return 0; /* no error */
 185
 186        if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
 187            ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
 188            ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
 189                /* Single bit (recoverable) error in data */
 190
 191                unsigned byte;
 192                unsigned bit;
 193
 194#ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 195                // swap the bytes to correct for the wrong order
 196                unsigned char t;
 197
 198                t = d0;
 199                d0 = d1;
 200                d1 = t;
 201#endif
 202
 203                bit = byte = 0;
 204
 205                if (d1 & 0x80)
 206                        byte |= 0x80;
 207                if (d1 & 0x20)
 208                        byte |= 0x40;
 209                if (d1 & 0x08)
 210                        byte |= 0x20;
 211                if (d1 & 0x02)
 212                        byte |= 0x10;
 213                if (d0 & 0x80)
 214                        byte |= 0x08;
 215                if (d0 & 0x20)
 216                        byte |= 0x04;
 217                if (d0 & 0x08)
 218                        byte |= 0x02;
 219                if (d0 & 0x02)
 220                        byte |= 0x01;
 221
 222                if (d2 & 0x80)
 223                        bit |= 0x04;
 224                if (d2 & 0x20)
 225                        bit |= 0x02;
 226                if (d2 & 0x08)
 227                        bit |= 0x01;
 228
 229                data[byte] ^= (1 << bit);
 230
 231                return 1; /* Corrected the error */
 232        }
 233
 234        if ((yaffs_CountBits(d0) +
 235             yaffs_CountBits(d1) +
 236             yaffs_CountBits(d2)) ==  1) {
 237                /* Reccoverable error in ecc */
 238
 239                read_ecc[0] = test_ecc[0];
 240                read_ecc[1] = test_ecc[1];
 241                read_ecc[2] = test_ecc[2];
 242
 243                return 1; /* Corrected the error */
 244        }
 245
 246        /* Unrecoverable error */
 247
 248        return -1;
 249
 250}
 251
 252
 253/*
 254 * ECCxxxOther does ECC calcs on arbitrary n bytes of data
 255 */
 256void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
 257                             yaffs_ECCOther * eccOther)
 258{
 259        unsigned int i;
 260
 261        unsigned char col_parity = 0;
 262        unsigned line_parity = 0;
 263        unsigned line_parity_prime = 0;
 264        unsigned char b;
 265
 266        for (i = 0; i < nBytes; i++) {
 267                b = column_parity_table[*data++];
 268                col_parity ^= b;
 269
 270                if (b & 0x01)    {
 271                        /* odd number of bits in the byte */
 272                        line_parity ^= i;
 273                        line_parity_prime ^= ~i;
 274                }
 275
 276        }
 277
 278        eccOther->colParity = (col_parity >> 2) & 0x3f;
 279        eccOther->lineParity = line_parity;
 280        eccOther->lineParityPrime = line_parity_prime;
 281}
 282
 283int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 284                          yaffs_ECCOther * read_ecc,
 285                          const yaffs_ECCOther * test_ecc)
 286{
 287        unsigned char cDelta;   /* column parity delta */
 288        unsigned lDelta;        /* line parity delta */
 289        unsigned lDeltaPrime;   /* line parity delta */
 290        unsigned bit;
 291
 292        cDelta = read_ecc->colParity ^ test_ecc->colParity;
 293        lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
 294        lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
 295
 296        if ((cDelta | lDelta | lDeltaPrime) == 0)
 297                return 0; /* no error */
 298
 299        if (lDelta == ~lDeltaPrime &&
 300            (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
 301        {
 302                /* Single bit (recoverable) error in data */
 303
 304                bit = 0;
 305
 306                if (cDelta & 0x20)
 307                        bit |= 0x04;
 308                if (cDelta & 0x08)
 309                        bit |= 0x02;
 310                if (cDelta & 0x02)
 311                        bit |= 0x01;
 312
 313                if(lDelta >= nBytes)
 314                        return -1;
 315
 316                data[lDelta] ^= (1 << bit);
 317
 318                return 1; /* corrected */
 319        }
 320
 321        if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
 322             yaffs_CountBits(cDelta)) == 1) {
 323                /* Reccoverable error in ecc */
 324
 325                *read_ecc = *test_ecc;
 326                return 1; /* corrected */
 327        }
 328
 329        /* Unrecoverable error */
 330
 331        return -1;
 332
 333}
 334