drivers/mtd/nand/nand_ecc.c

   1 /*
   2  * This file contains an ECC algorithm from Toshiba that detects and
   3  * corrects 1 bit errors in a 256 byte block of data.
   4  *
   5  * drivers/mtd/nand/nand_ecc.c
   6  *
   7  * Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
   8  *                         Toshiba America Electronics Components, Inc.
   9  *
  10  * $Id: nand_ecc.c,v 1.14 2004/06/16 15:34:37 gleixner Exp $
  11  *
  12  * This file is free software; you can redistribute it and/or modify it
  13  * under the terms of the GNU General Public License as published by the
  14  * Free Software Foundation; either version 2 or (at your option) any
  15  * later version.
  16  *
  17  * This file is distributed in the hope that it will be useful, but WITHOUT
  18  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  20  * for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License along
  23  * with this file; if not, write to the Free Software Foundation, Inc.,
  24  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  25  *
  26  * As a special exception, if other files instantiate templates or use
  27  * macros or inline functions from these files, or you compile these
  28  * files and link them with other works to produce a work based on these
  29  * files, these files do not by themselves cause the resulting work to be
  30  * covered by the GNU General Public License. However the source code for
  31  * these files must still be made available in accordance with section (3)
  32  * of the GNU General Public License.
  33  *
  34  * This exception does not invalidate any other reasons why a work based on
  35  * this file might be covered by the GNU General Public License.
  36  */
  37
  38 #include <linux/types.h>
  39 #include <linux/kernel.h>
  40 #include <linux/module.h>
  41 #include <linux/mtd/nand_ecc.h>
  42
  43 /*
  44  * Pre-calculated 256-way 1 byte column parity
  45  */
  46 static const u_char nand_ecc_precalc_table[] = {
  47         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
  48         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  49         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  50         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  51         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  52         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  53         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  54         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  55         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  56         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  57         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  58         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  59         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  60         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  61         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  62         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
  63 };
  64
  65
  66 /**
  67  * nand_trans_result - [GENERIC] create non-inverted ECC
  68  * @reg2:       line parity reg 2
  69  * @reg3:       line parity reg 3
  70  * @ecc_code:   ecc
  71  *
  72  * Creates non-inverted ECC code from line parity
  73  */
  74 static void nand_trans_result(u_char reg2, u_char reg3,
  75         u_char *ecc_code)
  76 {
  77         u_char a, b, i, tmp1, tmp2;
  78
  79         /* Initialize variables */
  80         a = b = 0x80;
  81         tmp1 = tmp2 = 0;
  82
  83         /* Calculate first ECC byte */
  84         for (i = 0; i < 4; i++) {
  85                 if (reg3 & a)           /* LP15,13,11,9 --> ecc_code[0] */
  86                         tmp1 |= b;
  87                 b >>= 1;
  88                 if (reg2 & a)           /* LP14,12,10,8 --> ecc_code[0] */
  89                         tmp1 |= b;
  90                 b >>= 1;
  91                 a >>= 1;
  92         }
  93
  94         /* Calculate second ECC byte */
  95         b = 0x80;
  96         for (i = 0; i < 4; i++) {
  97                 if (reg3 & a)           /* LP7,5,3,1 --> ecc_code[1] */
  98                         tmp2 |= b;
  99                 b >>= 1;
 100                 if (reg2 & a)           /* LP6,4,2,0 --> ecc_code[1] */
 101                         tmp2 |= b;
 102                 b >>= 1;
 103                 a >>= 1;
 104         }
 105
 106         /* Store two of the ECC bytes */
 107         ecc_code[0] = tmp1;
 108         ecc_code[1] = tmp2;
 109 }
 110
 111 /**
 112  * nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
 113  * @mtd:        MTD block structure
 114  * @dat:        raw data
 115  * @ecc_code:   buffer for ECC
 116  */
 117 int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
 118 {
 119         u_char idx, reg1, reg2, reg3;
 120         int j;
 121
 122         /* Initialize variables */
 123         reg1 = reg2 = reg3 = 0;
 124         ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
 125
 126         /* Build up column parity */
 127         for(j = 0; j < 256; j++) {
 128
 129                 /* Get CP0 - CP5 from table */
 130                 idx = nand_ecc_precalc_table[dat[j]];
 131                 reg1 ^= (idx & 0x3f);
 132
 133                 /* All bit XOR = 1 ? */
 134                 if (idx & 0x40) {
 135                         reg3 ^= (u_char) j;
 136                         reg2 ^= ~((u_char) j);
 137                 }
 138         }
 139
 140         /* Create non-inverted ECC code from line parity */
 141         nand_trans_result(reg2, reg3, ecc_code);
 142
 143         /* Calculate final ECC code */
 144         ecc_code[0] = ~ecc_code[0];
 145         ecc_code[1] = ~ecc_code[1];
 146         ecc_code[2] = ((~reg1) << 2) | 0x03;
 147         return 0;
 148 }
 149
 150 /**
 151  * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 152  * @mtd:        MTD block structure
 153  * @dat:        raw data read from the chip
 154  * @read_ecc:   ECC from the chip
 155  * @calc_ecc:   the ECC calculated from raw data
 156  *
 157  * Detect and correct a 1 bit error for 256 byte block
 158  */
 159 int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
 160 {
 161         u_char a, b, c, d1, d2, d3, add, bit, i;
 162
 163         /* Do error detection */
 164         d1 = calc_ecc[0] ^ read_ecc[0];
 165         d2 = calc_ecc[1] ^ read_ecc[1];
 166         d3 = calc_ecc[2] ^ read_ecc[2];
 167
 168         if ((d1 | d2 | d3) == 0) {
 169                 /* No errors */
 170                 return 0;
 171         }
 172         else {
 173                 a = (d1 ^ (d1 >> 1)) & 0x55;
 174                 b = (d2 ^ (d2 >> 1)) & 0x55;
 175                 c = (d3 ^ (d3 >> 1)) & 0x54;
 176
 177                 /* Found and will correct single bit error in the data */
 178                 if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
 179                         c = 0x80;
 180                         add = 0;
 181                         a = 0x80;
 182                         for (i=0; i<4; i++) {
 183                                 if (d1 & c)
 184                                         add |= a;
 185                                 c >>= 2;
 186                                 a >>= 1;
 187                         }
 188                         c = 0x80;
 189                         for (i=0; i<4; i++) {
 190                                 if (d2 & c)
 191                                         add |= a;
 192                                 c >>= 2;
 193                                 a >>= 1;
 194                         }
 195                         bit = 0;
 196                         b = 0x04;
 197                         c = 0x80;
 198                         for (i=0; i<3; i++) {
 199                                 if (d3 & c)
 200                                         bit |= b;
 201                                 c >>= 2;
 202                                 b >>= 1;
 203                         }
 204                         b = 0x01;
 205                         a = dat[add];
 206                         a ^= (b << bit);
 207                         dat[add] = a;
 208                         return 1;
 209                 }
 210                 else {
 211                         i = 0;
 212                         while (d1) {
 213                                 if (d1 & 0x01)
 214                                         ++i;
 215                                 d1 >>= 1;
 216                         }
 217                         while (d2) {
 218                                 if (d2 & 0x01)
 219                                         ++i;
 220                                 d2 >>= 1;
 221                         }
 222                         while (d3) {
 223                                 if (d3 & 0x01)
 224                                         ++i;
 225                                 d3 >>= 1;
 226                         }
 227                         if (i == 1) {
 228                                 /* ECC Code Error Correction */
 229                                 read_ecc[0] = calc_ecc[0];
 230                                 read_ecc[1] = calc_ecc[1];
 231                                 read_ecc[2] = calc_ecc[2];
 232                                 return 2;
 233                         }
 234                         else {
 235                                 /* Uncorrectable Error */
 236                                 return -1;
 237                         }
 238                 }
 239         }
 240
 241         /* Should never happen */
 242         return -1;
 243 }
 244
 245 EXPORT_SYMBOL(nand_calculate_ecc);
 246 EXPORT_SYMBOL(nand_correct_data);
 247
 248 MODULE_LICENSE("GPL");
 249 MODULE_AUTHOR("Steven J. Hill <sjhill@realitydiluted.com>");
 250 MODULE_DESCRIPTION("Generic NAND ECC support");