target/linux/generic-2.6/files/fs/yaffs2/yaffs_ecc.c

   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 const char *yaffs_ecc_c_version =
  32
  33 #include "yportenv.h"
  34
  35 #include "yaffs_ecc.h"
  36
  37 static const unsigned char column_parity_table[] = {
  38         0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  39         0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  40         0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  41         0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  42         0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  43         0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  44         0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  45         0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  46         0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  47         0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  48         0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  49         0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  50         0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  51         0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  52         0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  53         0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  54         0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  55         0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  56         0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  57         0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  58         0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  59         0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  60         0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  61         0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  62         0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  63         0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  64         0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  65         0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  66         0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  67         0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  68         0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  69         0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  70 };
  71
  72 /* Count the bits in an unsigned char or a U32 */
  73
  74 static int yaffs_CountBits(unsigned char x)
  75 {
  76         int r = 0;
  77         while (x) {
  78                 if (x & 1)
  79                         r++;
  80                 x >>= 1;
  81         }
  82         return r;
  83 }
  84
  85 static int yaffs_CountBits32(unsigned x)
  86 {
  87         int r = 0;
  88         while (x) {
  89                 if (x & 1)
  90                         r++;
  91                 x >>= 1;
  92         }
  93         return r;
  94 }
  95
  96 /* Calculate the ECC for a 256-byte block of data */
  97 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
  98 {
  99         unsigned int i;
 100
 101         unsigned char col_parity = 0;
 102         unsigned char line_parity = 0;
 103         unsigned char line_parity_prime = 0;
 104         unsigned char t;
 105         unsigned char b;
 106
 107         for (i = 0; i < 256; i++) {
 108                 b = column_parity_table[*data++];
 109                 col_parity ^= b;
 110
 111                 if (b & 0x01)   // odd number of bits in the byte
 112                 {
 113                         line_parity ^= i;
 114                         line_parity_prime ^= ~i;
 115                 }
 116
 117         }
 118
 119         ecc[2] = (~col_parity) | 0x03;
 120
 121         t = 0;
 122         if (line_parity & 0x80)
 123                 t |= 0x80;
 124         if (line_parity_prime & 0x80)
 125                 t |= 0x40;
 126         if (line_parity & 0x40)
 127                 t |= 0x20;
 128         if (line_parity_prime & 0x40)
 129                 t |= 0x10;
 130         if (line_parity & 0x20)
 131                 t |= 0x08;
 132         if (line_parity_prime & 0x20)
 133                 t |= 0x04;
 134         if (line_parity & 0x10)
 135                 t |= 0x02;
 136         if (line_parity_prime & 0x10)
 137                 t |= 0x01;
 138         ecc[1] = ~t;
 139
 140         t = 0;
 141         if (line_parity & 0x08)
 142                 t |= 0x80;
 143         if (line_parity_prime & 0x08)
 144                 t |= 0x40;
 145         if (line_parity & 0x04)
 146                 t |= 0x20;
 147         if (line_parity_prime & 0x04)
 148                 t |= 0x10;
 149         if (line_parity & 0x02)
 150                 t |= 0x08;
 151         if (line_parity_prime & 0x02)
 152                 t |= 0x04;
 153         if (line_parity & 0x01)
 154                 t |= 0x02;
 155         if (line_parity_prime & 0x01)
 156                 t |= 0x01;
 157         ecc[0] = ~t;
 158
 159 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 160         // Swap the bytes into the wrong order
 161         t = ecc[0];
 162         ecc[0] = ecc[1];
 163         ecc[1] = t;
 164 #endif
 165 }
 166
 167
 168 /* Correct the ECC on a 256 byte block of data */
 169
 170 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
 171                      const unsigned char *test_ecc)
 172 {
 173         unsigned char d0, d1, d2;       /* deltas */
 174
 175         d0 = read_ecc[0] ^ test_ecc[0];
 176         d1 = read_ecc[1] ^ test_ecc[1];
 177         d2 = read_ecc[2] ^ test_ecc[2];
 178
 179         if ((d0 | d1 | d2) == 0)
 180                 return 0; /* no error */
 181
 182         if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
 183             ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
 184             ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
 185                 /* Single bit (recoverable) error in data */
 186
 187                 unsigned byte;
 188                 unsigned bit;
 189
 190 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 191                 // swap the bytes to correct for the wrong order
 192                 unsigned char t;
 193
 194                 t = d0;
 195                 d0 = d1;
 196                 d1 = t;
 197 #endif
 198
 199                 bit = byte = 0;
 200
 201                 if (d1 & 0x80)
 202                         byte |= 0x80;
 203                 if (d1 & 0x20)
 204                         byte |= 0x40;
 205                 if (d1 & 0x08)
 206                         byte |= 0x20;
 207                 if (d1 & 0x02)
 208                         byte |= 0x10;
 209                 if (d0 & 0x80)
 210                         byte |= 0x08;
 211                 if (d0 & 0x20)
 212                         byte |= 0x04;
 213                 if (d0 & 0x08)
 214                         byte |= 0x02;
 215                 if (d0 & 0x02)
 216                         byte |= 0x01;
 217
 218                 if (d2 & 0x80)
 219                         bit |= 0x04;
 220                 if (d2 & 0x20)
 221                         bit |= 0x02;
 222                 if (d2 & 0x08)
 223                         bit |= 0x01;
 224
 225                 data[byte] ^= (1 << bit);
 226
 227                 return 1; /* Corrected the error */
 228         }
 229
 230         if ((yaffs_CountBits(d0) +
 231              yaffs_CountBits(d1) +
 232              yaffs_CountBits(d2)) ==  1) {
 233                 /* Reccoverable error in ecc */
 234
 235                 read_ecc[0] = test_ecc[0];
 236                 read_ecc[1] = test_ecc[1];
 237                 read_ecc[2] = test_ecc[2];
 238
 239                 return 1; /* Corrected the error */
 240         }
 241
 242         /* Unrecoverable error */
 243
 244         return -1;
 245
 246 }
 247
 248
 249 /*
 250  * ECCxxxOther does ECC calcs on arbitrary n bytes of data
 251  */
 252 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
 253                              yaffs_ECCOther * eccOther)
 254 {
 255         unsigned int i;
 256
 257         unsigned char col_parity = 0;
 258         unsigned line_parity = 0;
 259         unsigned line_parity_prime = 0;
 260         unsigned char b;
 261
 262         for (i = 0; i < nBytes; i++) {
 263                 b = column_parity_table[*data++];
 264                 col_parity ^= b;
 265
 266                 if (b & 0x01)    {
 267                         /* odd number of bits in the byte */
 268                         line_parity ^= i;
 269                         line_parity_prime ^= ~i;
 270                 }
 271
 272         }
 273
 274         eccOther->colParity = (col_parity >> 2) & 0x3f;
 275         eccOther->lineParity = line_parity;
 276         eccOther->lineParityPrime = line_parity_prime;
 277 }
 278
 279 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 280                           yaffs_ECCOther * read_ecc,
 281                           const yaffs_ECCOther * test_ecc)
 282 {
 283         unsigned char cDelta;   /* column parity delta */
 284         unsigned lDelta;        /* line parity delta */
 285         unsigned lDeltaPrime;   /* line parity delta */
 286         unsigned bit;
 287
 288         cDelta = read_ecc->colParity ^ test_ecc->colParity;
 289         lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
 290         lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
 291
 292         if ((cDelta | lDelta | lDeltaPrime) == 0)
 293                 return 0; /* no error */
 294
 295         if (lDelta == ~lDeltaPrime &&
 296             (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15))
 297         {
 298                 /* Single bit (recoverable) error in data */
 299
 300                 bit = 0;
 301
 302                 if (cDelta & 0x20)
 303                         bit |= 0x04;
 304                 if (cDelta & 0x08)
 305                         bit |= 0x02;
 306                 if (cDelta & 0x02)
 307                         bit |= 0x01;
 308
 309                 if(lDelta >= nBytes)
 310                         return -1;
 311
 312                 data[lDelta] ^= (1 << bit);
 313
 314                 return 1; /* corrected */
 315         }
 316
 317         if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
 318              yaffs_CountBits(cDelta)) == 1) {
 319                 /* Reccoverable error in ecc */
 320
 321                 *read_ecc = *test_ecc;
 322                 return 1; /* corrected */
 323         }
 324
 325         /* Unrecoverable error */
 326
 327         return -1;
 328
 329 }
 330