target/linux/generic/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         "$Id: yaffs_ecc.c,v 1.11 2009-03-06 17:20:50 wookey Exp $";
  33
  34 #include "yportenv.h"
  35
  36 #include "yaffs_ecc.h"
  37
  38 static const unsigned char column_parity_table[] = {
  39         0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  40         0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  41         0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  42         0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  43         0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  44         0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  45         0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  46         0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  47         0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  48         0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  49         0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  50         0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  51         0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  52         0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  53         0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  54         0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  55         0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
  56         0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
  57         0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
  58         0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
  59         0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
  60         0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
  61         0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
  62         0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
  63         0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
  64         0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
  65         0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
  66         0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
  67         0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
  68         0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
  69         0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
  70         0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
  71 };
  72
  73 /* Count the bits in an unsigned char or a U32 */
  74
  75 static int yaffs_CountBits(unsigned char x)
  76 {
  77         int r = 0;
  78         while (x) {
  79                 if (x & 1)
  80                         r++;
  81                 x >>= 1;
  82         }
  83         return r;
  84 }
  85
  86 static int yaffs_CountBits32(unsigned x)
  87 {
  88         int r = 0;
  89         while (x) {
  90                 if (x & 1)
  91                         r++;
  92                 x >>= 1;
  93         }
  94         return r;
  95 }
  96
  97 /* Calculate the ECC for a 256-byte block of data */
  98 void yaffs_ECCCalculate(const unsigned char *data, unsigned char *ecc)
  99 {
 100         unsigned int i;
 101
 102         unsigned char col_parity = 0;
 103         unsigned char line_parity = 0;
 104         unsigned char line_parity_prime = 0;
 105         unsigned char t;
 106         unsigned char b;
 107
 108         for (i = 0; i < 256; i++) {
 109                 b = column_parity_table[*data++];
 110                 col_parity ^= b;
 111
 112                 if (b & 0x01) {         /* odd number of bits in the byte */
 113                         line_parity ^= i;
 114                         line_parity_prime ^= ~i;
 115                 }
 116         }
 117
 118         ecc[2] = (~col_parity) | 0x03;
 119
 120         t = 0;
 121         if (line_parity & 0x80)
 122                 t |= 0x80;
 123         if (line_parity_prime & 0x80)
 124                 t |= 0x40;
 125         if (line_parity & 0x40)
 126                 t |= 0x20;
 127         if (line_parity_prime & 0x40)
 128                 t |= 0x10;
 129         if (line_parity & 0x20)
 130                 t |= 0x08;
 131         if (line_parity_prime & 0x20)
 132                 t |= 0x04;
 133         if (line_parity & 0x10)
 134                 t |= 0x02;
 135         if (line_parity_prime & 0x10)
 136                 t |= 0x01;
 137         ecc[1] = ~t;
 138
 139         t = 0;
 140         if (line_parity & 0x08)
 141                 t |= 0x80;
 142         if (line_parity_prime & 0x08)
 143                 t |= 0x40;
 144         if (line_parity & 0x04)
 145                 t |= 0x20;
 146         if (line_parity_prime & 0x04)
 147                 t |= 0x10;
 148         if (line_parity & 0x02)
 149                 t |= 0x08;
 150         if (line_parity_prime & 0x02)
 151                 t |= 0x04;
 152         if (line_parity & 0x01)
 153                 t |= 0x02;
 154         if (line_parity_prime & 0x01)
 155                 t |= 0x01;
 156         ecc[0] = ~t;
 157
 158 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 159         /* Swap the bytes into the wrong order */
 160         t = ecc[0];
 161         ecc[0] = ecc[1];
 162         ecc[1] = t;
 163 #endif
 164 }
 165
 166
 167 /* Correct the ECC on a 256 byte block of data */
 168
 169 int yaffs_ECCCorrect(unsigned char *data, unsigned char *read_ecc,
 170                      const unsigned char *test_ecc)
 171 {
 172         unsigned char d0, d1, d2;       /* deltas */
 173
 174         d0 = read_ecc[0] ^ test_ecc[0];
 175         d1 = read_ecc[1] ^ test_ecc[1];
 176         d2 = read_ecc[2] ^ test_ecc[2];
 177
 178         if ((d0 | d1 | d2) == 0)
 179                 return 0; /* no error */
 180
 181         if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
 182             ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
 183             ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
 184                 /* Single bit (recoverable) error in data */
 185
 186                 unsigned byte;
 187                 unsigned bit;
 188
 189 #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER
 190                 /* swap the bytes to correct for the wrong order */
 191                 unsigned char t;
 192
 193                 t = d0;
 194                 d0 = d1;
 195                 d1 = t;
 196 #endif
 197
 198                 bit = byte = 0;
 199
 200                 if (d1 & 0x80)
 201                         byte |= 0x80;
 202                 if (d1 & 0x20)
 203                         byte |= 0x40;
 204                 if (d1 & 0x08)
 205                         byte |= 0x20;
 206                 if (d1 & 0x02)
 207                         byte |= 0x10;
 208                 if (d0 & 0x80)
 209                         byte |= 0x08;
 210                 if (d0 & 0x20)
 211                         byte |= 0x04;
 212                 if (d0 & 0x08)
 213                         byte |= 0x02;
 214                 if (d0 & 0x02)
 215                         byte |= 0x01;
 216
 217                 if (d2 & 0x80)
 218                         bit |= 0x04;
 219                 if (d2 & 0x20)
 220                         bit |= 0x02;
 221                 if (d2 & 0x08)
 222                         bit |= 0x01;
 223
 224                 data[byte] ^= (1 << bit);
 225
 226                 return 1; /* Corrected the error */
 227         }
 228
 229         if ((yaffs_CountBits(d0) +
 230              yaffs_CountBits(d1) +
 231              yaffs_CountBits(d2)) ==  1) {
 232                 /* Reccoverable error in ecc */
 233
 234                 read_ecc[0] = test_ecc[0];
 235                 read_ecc[1] = test_ecc[1];
 236                 read_ecc[2] = test_ecc[2];
 237
 238                 return 1; /* Corrected the error */
 239         }
 240
 241         /* Unrecoverable error */
 242
 243         return -1;
 244
 245 }
 246
 247
 248 /*
 249  * ECCxxxOther does ECC calcs on arbitrary n bytes of data
 250  */
 251 void yaffs_ECCCalculateOther(const unsigned char *data, unsigned nBytes,
 252                                 yaffs_ECCOther *eccOther)
 253 {
 254         unsigned int i;
 255
 256         unsigned char col_parity = 0;
 257         unsigned line_parity = 0;
 258         unsigned line_parity_prime = 0;
 259         unsigned char b;
 260
 261         for (i = 0; i < nBytes; i++) {
 262                 b = column_parity_table[*data++];
 263                 col_parity ^= b;
 264
 265                 if (b & 0x01)    {
 266                         /* odd number of bits in the byte */
 267                         line_parity ^= i;
 268                         line_parity_prime ^= ~i;
 269                 }
 270
 271         }
 272
 273         eccOther->colParity = (col_parity >> 2) & 0x3f;
 274         eccOther->lineParity = line_parity;
 275         eccOther->lineParityPrime = line_parity_prime;
 276 }
 277
 278 int yaffs_ECCCorrectOther(unsigned char *data, unsigned nBytes,
 279                         yaffs_ECCOther *read_ecc,
 280                         const yaffs_ECCOther *test_ecc)
 281 {
 282         unsigned char cDelta;   /* column parity delta */
 283         unsigned lDelta;        /* line parity delta */
 284         unsigned lDeltaPrime;   /* line parity delta */
 285         unsigned bit;
 286
 287         cDelta = read_ecc->colParity ^ test_ecc->colParity;
 288         lDelta = read_ecc->lineParity ^ test_ecc->lineParity;
 289         lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime;
 290
 291         if ((cDelta | lDelta | lDeltaPrime) == 0)
 292                 return 0; /* no error */
 293
 294         if (lDelta == ~lDeltaPrime &&
 295             (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) {
 296                 /* Single bit (recoverable) error in data */
 297
 298                 bit = 0;
 299
 300                 if (cDelta & 0x20)
 301                         bit |= 0x04;
 302                 if (cDelta & 0x08)
 303                         bit |= 0x02;
 304                 if (cDelta & 0x02)
 305                         bit |= 0x01;
 306
 307                 if (lDelta >= nBytes)
 308                         return -1;
 309
 310                 data[lDelta] ^= (1 << bit);
 311
 312                 return 1; /* corrected */
 313         }
 314
 315         if ((yaffs_CountBits32(lDelta) + yaffs_CountBits32(lDeltaPrime) +
 316                         yaffs_CountBits(cDelta)) == 1) {
 317                 /* Reccoverable error in ecc */
 318
 319                 *read_ecc = *test_ecc;
 320                 return 1; /* corrected */
 321         }
 322
 323         /* Unrecoverable error */
 324
 325         return -1;
 326 }