| 1 | /* |
| 2 | * YAFFS: Yet Another Flash File System. A NAND-flash specific file system. |
| 3 | * |
| 4 | * Copyright (C) 2002-2010 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 | #include "yportenv.h" |
| 32 | |
| 33 | #include "yaffs_ecc.h" |
| 34 | |
| 35 | static const unsigned char column_parity_table[] = { |
| 36 | 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, |
| 37 | 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, |
| 38 | 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, |
| 39 | 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, |
| 40 | 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, |
| 41 | 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, |
| 42 | 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, |
| 43 | 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, |
| 44 | 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, |
| 45 | 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, |
| 46 | 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, |
| 47 | 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, |
| 48 | 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, |
| 49 | 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, |
| 50 | 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, |
| 51 | 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, |
| 52 | 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0, |
| 53 | 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9, |
| 54 | 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55, |
| 55 | 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c, |
| 56 | 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59, |
| 57 | 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30, |
| 58 | 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc, |
| 59 | 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5, |
| 60 | 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65, |
| 61 | 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c, |
| 62 | 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0, |
| 63 | 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99, |
| 64 | 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc, |
| 65 | 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95, |
| 66 | 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69, |
| 67 | 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00, |
| 68 | }; |
| 69 | |
| 70 | /* Count the bits in an unsigned char or a U32 */ |
| 71 | |
| 72 | static int yaffs_count_bits(unsigned char x) |
| 73 | { |
| 74 | int r = 0; |
| 75 | while (x) { |
| 76 | if (x & 1) |
| 77 | r++; |
| 78 | x >>= 1; |
| 79 | } |
| 80 | return r; |
| 81 | } |
| 82 | |
| 83 | static int yaffs_count_bits32(unsigned x) |
| 84 | { |
| 85 | int r = 0; |
| 86 | while (x) { |
| 87 | if (x & 1) |
| 88 | r++; |
| 89 | x >>= 1; |
| 90 | } |
| 91 | return r; |
| 92 | } |
| 93 | |
| 94 | /* Calculate the ECC for a 256-byte block of data */ |
| 95 | void yaffs_ecc_cacl(const unsigned char *data, unsigned char *ecc) |
| 96 | { |
| 97 | unsigned int i; |
| 98 | |
| 99 | unsigned char col_parity = 0; |
| 100 | unsigned char line_parity = 0; |
| 101 | unsigned char line_parity_prime = 0; |
| 102 | unsigned char t; |
| 103 | unsigned char b; |
| 104 | |
| 105 | for (i = 0; i < 256; i++) { |
| 106 | b = column_parity_table[*data++]; |
| 107 | col_parity ^= b; |
| 108 | |
| 109 | if (b & 0x01) { /* odd number of bits in the byte */ |
| 110 | line_parity ^= i; |
| 111 | line_parity_prime ^= ~i; |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | ecc[2] = (~col_parity) | 0x03; |
| 116 | |
| 117 | t = 0; |
| 118 | if (line_parity & 0x80) |
| 119 | t |= 0x80; |
| 120 | if (line_parity_prime & 0x80) |
| 121 | t |= 0x40; |
| 122 | if (line_parity & 0x40) |
| 123 | t |= 0x20; |
| 124 | if (line_parity_prime & 0x40) |
| 125 | t |= 0x10; |
| 126 | if (line_parity & 0x20) |
| 127 | t |= 0x08; |
| 128 | if (line_parity_prime & 0x20) |
| 129 | t |= 0x04; |
| 130 | if (line_parity & 0x10) |
| 131 | t |= 0x02; |
| 132 | if (line_parity_prime & 0x10) |
| 133 | t |= 0x01; |
| 134 | ecc[1] = ~t; |
| 135 | |
| 136 | t = 0; |
| 137 | if (line_parity & 0x08) |
| 138 | t |= 0x80; |
| 139 | if (line_parity_prime & 0x08) |
| 140 | t |= 0x40; |
| 141 | if (line_parity & 0x04) |
| 142 | t |= 0x20; |
| 143 | if (line_parity_prime & 0x04) |
| 144 | t |= 0x10; |
| 145 | if (line_parity & 0x02) |
| 146 | t |= 0x08; |
| 147 | if (line_parity_prime & 0x02) |
| 148 | t |= 0x04; |
| 149 | if (line_parity & 0x01) |
| 150 | t |= 0x02; |
| 151 | if (line_parity_prime & 0x01) |
| 152 | t |= 0x01; |
| 153 | ecc[0] = ~t; |
| 154 | |
| 155 | #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER |
| 156 | /* Swap the bytes into the wrong order */ |
| 157 | t = ecc[0]; |
| 158 | ecc[0] = ecc[1]; |
| 159 | ecc[1] = t; |
| 160 | #endif |
| 161 | } |
| 162 | |
| 163 | |
| 164 | /* Correct the ECC on a 256 byte block of data */ |
| 165 | |
| 166 | int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc, |
| 167 | const unsigned char *test_ecc) |
| 168 | { |
| 169 | unsigned char d0, d1, d2; /* deltas */ |
| 170 | |
| 171 | d0 = read_ecc[0] ^ test_ecc[0]; |
| 172 | d1 = read_ecc[1] ^ test_ecc[1]; |
| 173 | d2 = read_ecc[2] ^ test_ecc[2]; |
| 174 | |
| 175 | if ((d0 | d1 | d2) == 0) |
| 176 | return 0; /* no error */ |
| 177 | |
| 178 | if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 && |
| 179 | ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 && |
| 180 | ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) { |
| 181 | /* Single bit (recoverable) error in data */ |
| 182 | |
| 183 | unsigned byte; |
| 184 | unsigned bit; |
| 185 | |
| 186 | #ifdef CONFIG_YAFFS_ECC_WRONG_ORDER |
| 187 | /* swap the bytes to correct for the wrong order */ |
| 188 | unsigned char t; |
| 189 | |
| 190 | t = d0; |
| 191 | d0 = d1; |
| 192 | d1 = t; |
| 193 | #endif |
| 194 | |
| 195 | bit = byte = 0; |
| 196 | |
| 197 | if (d1 & 0x80) |
| 198 | byte |= 0x80; |
| 199 | if (d1 & 0x20) |
| 200 | byte |= 0x40; |
| 201 | if (d1 & 0x08) |
| 202 | byte |= 0x20; |
| 203 | if (d1 & 0x02) |
| 204 | byte |= 0x10; |
| 205 | if (d0 & 0x80) |
| 206 | byte |= 0x08; |
| 207 | if (d0 & 0x20) |
| 208 | byte |= 0x04; |
| 209 | if (d0 & 0x08) |
| 210 | byte |= 0x02; |
| 211 | if (d0 & 0x02) |
| 212 | byte |= 0x01; |
| 213 | |
| 214 | if (d2 & 0x80) |
| 215 | bit |= 0x04; |
| 216 | if (d2 & 0x20) |
| 217 | bit |= 0x02; |
| 218 | if (d2 & 0x08) |
| 219 | bit |= 0x01; |
| 220 | |
| 221 | data[byte] ^= (1 << bit); |
| 222 | |
| 223 | return 1; /* Corrected the error */ |
| 224 | } |
| 225 | |
| 226 | if ((yaffs_count_bits(d0) + |
| 227 | yaffs_count_bits(d1) + |
| 228 | yaffs_count_bits(d2)) == 1) { |
| 229 | /* Reccoverable error in ecc */ |
| 230 | |
| 231 | read_ecc[0] = test_ecc[0]; |
| 232 | read_ecc[1] = test_ecc[1]; |
| 233 | read_ecc[2] = test_ecc[2]; |
| 234 | |
| 235 | return 1; /* Corrected the error */ |
| 236 | } |
| 237 | |
| 238 | /* Unrecoverable error */ |
| 239 | |
| 240 | return -1; |
| 241 | |
| 242 | } |
| 243 | |
| 244 | |
| 245 | /* |
| 246 | * ECCxxxOther does ECC calcs on arbitrary n bytes of data |
| 247 | */ |
| 248 | void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes, |
| 249 | yaffs_ECCOther *eccOther) |
| 250 | { |
| 251 | unsigned int i; |
| 252 | |
| 253 | unsigned char col_parity = 0; |
| 254 | unsigned line_parity = 0; |
| 255 | unsigned line_parity_prime = 0; |
| 256 | unsigned char b; |
| 257 | |
| 258 | for (i = 0; i < n_bytes; i++) { |
| 259 | b = column_parity_table[*data++]; |
| 260 | col_parity ^= b; |
| 261 | |
| 262 | if (b & 0x01) { |
| 263 | /* odd number of bits in the byte */ |
| 264 | line_parity ^= i; |
| 265 | line_parity_prime ^= ~i; |
| 266 | } |
| 267 | |
| 268 | } |
| 269 | |
| 270 | eccOther->colParity = (col_parity >> 2) & 0x3f; |
| 271 | eccOther->lineParity = line_parity; |
| 272 | eccOther->lineParityPrime = line_parity_prime; |
| 273 | } |
| 274 | |
| 275 | int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes, |
| 276 | yaffs_ECCOther *read_ecc, |
| 277 | const yaffs_ECCOther *test_ecc) |
| 278 | { |
| 279 | unsigned char cDelta; /* column parity delta */ |
| 280 | unsigned lDelta; /* line parity delta */ |
| 281 | unsigned lDeltaPrime; /* line parity delta */ |
| 282 | unsigned bit; |
| 283 | |
| 284 | cDelta = read_ecc->colParity ^ test_ecc->colParity; |
| 285 | lDelta = read_ecc->lineParity ^ test_ecc->lineParity; |
| 286 | lDeltaPrime = read_ecc->lineParityPrime ^ test_ecc->lineParityPrime; |
| 287 | |
| 288 | if ((cDelta | lDelta | lDeltaPrime) == 0) |
| 289 | return 0; /* no error */ |
| 290 | |
| 291 | if (lDelta == ~lDeltaPrime && |
| 292 | (((cDelta ^ (cDelta >> 1)) & 0x15) == 0x15)) { |
| 293 | /* Single bit (recoverable) error in data */ |
| 294 | |
| 295 | bit = 0; |
| 296 | |
| 297 | if (cDelta & 0x20) |
| 298 | bit |= 0x04; |
| 299 | if (cDelta & 0x08) |
| 300 | bit |= 0x02; |
| 301 | if (cDelta & 0x02) |
| 302 | bit |= 0x01; |
| 303 | |
| 304 | if (lDelta >= n_bytes) |
| 305 | return -1; |
| 306 | |
| 307 | data[lDelta] ^= (1 << bit); |
| 308 | |
| 309 | return 1; /* corrected */ |
| 310 | } |
| 311 | |
| 312 | if ((yaffs_count_bits32(lDelta) + yaffs_count_bits32(lDeltaPrime) + |
| 313 | yaffs_count_bits(cDelta)) == 1) { |
| 314 | /* Reccoverable error in ecc */ |
| 315 | |
| 316 | *read_ecc = *test_ecc; |
| 317 | return 1; /* corrected */ |
| 318 | } |
| 319 | |
| 320 | /* Unrecoverable error */ |
| 321 | |
| 322 | return -1; |
| 323 | } |
| 324 | |
