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 1.15 2005/11/07 11:14:30 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  * nand_trans_result - [GENERIC] create non-inverted ECC
  67  * @reg2:       line parity reg 2
  68  * @reg3:       line parity reg 3
  69  * @ecc_code:   ecc
  70  *
  71  * Creates non-inverted ECC code from line parity
  72  */
  73 static void nand_trans_result(u_char reg2, u_char reg3, u_char *ecc_code)
  74 {
  75         u_char a, b, i, tmp1, tmp2;
  76
  77         /* Initialize variables */
  78         a = b = 0x80;
  79         tmp1 = tmp2 = 0;
  80
  81         /* Calculate first ECC byte */
  82         for (i = 0; i < 4; i++) {
  83                 if (reg3 & a)   /* LP15,13,11,9 --> ecc_code[0] */
  84                         tmp1 |= b;
  85                 b >>= 1;
  86                 if (reg2 & a)   /* LP14,12,10,8 --> ecc_code[0] */
  87                         tmp1 |= b;
  88                 b >>= 1;
  89                 a >>= 1;
  90         }
  91
  92         /* Calculate second ECC byte */
  93         b = 0x80;
  94         for (i = 0; i < 4; i++) {
  95                 if (reg3 & a)   /* LP7,5,3,1 --> ecc_code[1] */
  96                         tmp2 |= b;
  97                 b >>= 1;
  98                 if (reg2 & a)   /* LP6,4,2,0 --> ecc_code[1] */
  99                         tmp2 |= b;
 100                 b >>= 1;
 101                 a >>= 1;
 102         }
 103
 104         /* Store two of the ECC bytes */
 105         ecc_code[0] = tmp1;
 106         ecc_code[1] = tmp2;
 107 }
 108
 109 /**
 110  * nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
 111  * @mtd:        MTD block structure
 112  * @dat:        raw data
 113  * @ecc_code:   buffer for ECC
 114  */
 115 int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
 116 {
 117         u_char idx, reg1, reg2, reg3;
 118         int j;
 119
 120         /* Initialize variables */
 121         reg1 = reg2 = reg3 = 0;
 122         ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
 123
 124         /* Build up column parity */
 125         for (j = 0; j < 256; j++) {
 126
 127                 /* Get CP0 - CP5 from table */
 128                 idx = nand_ecc_precalc_table[dat[j]];
 129                 reg1 ^= (idx & 0x3f);
 130
 131                 /* All bit XOR = 1 ? */
 132                 if (idx & 0x40) {
 133                         reg3 ^= (u_char) j;
 134                         reg2 ^= ~((u_char) j);
 135                 }
 136         }
 137
 138         /* Create non-inverted ECC code from line parity */
 139         nand_trans_result(reg2, reg3, ecc_code);
 140
 141         /* Calculate final ECC code */
 142         ecc_code[0] = ~ecc_code[0];
 143         ecc_code[1] = ~ecc_code[1];
 144         ecc_code[2] = ((~reg1) << 2) | 0x03;
 145         return 0;
 146 }
 147
 148 /**
 149  * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 150  * @mtd:        MTD block structure
 151  * @dat:        raw data read from the chip
 152  * @read_ecc:   ECC from the chip
 153  * @calc_ecc:   the ECC calculated from raw data
 154  *
 155  * Detect and correct a 1 bit error for 256 byte block
 156  */
 157 int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
 158 {
 159         u_char a, b, c, d1, d2, d3, add, bit, i;
 160
 161         /* Do error detection */
 162         d1 = calc_ecc[0] ^ read_ecc[0];
 163         d2 = calc_ecc[1] ^ read_ecc[1];
 164         d3 = calc_ecc[2] ^ read_ecc[2];
 165
 166         if ((d1 | d2 | d3) == 0) {
 167                 /* No errors */
 168                 return 0;
 169         } else {
 170                 a = (d1 ^ (d1 >> 1)) & 0x55;
 171                 b = (d2 ^ (d2 >> 1)) & 0x55;
 172                 c = (d3 ^ (d3 >> 1)) & 0x54;
 173
 174                 /* Found and will correct single bit error in the data */
 175                 if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
 176                         c = 0x80;
 177                         add = 0;
 178                         a = 0x80;
 179                         for (i = 0; i < 4; i++) {
 180                                 if (d1 & c)
 181                                         add |= a;
 182                                 c >>= 2;
 183                                 a >>= 1;
 184                         }
 185                         c = 0x80;
 186                         for (i = 0; i < 4; i++) {
 187                                 if (d2 & c)
 188                                         add |= a;
 189                                 c >>= 2;
 190                                 a >>= 1;
 191                         }
 192                         bit = 0;
 193                         b = 0x04;
 194                         c = 0x80;
 195                         for (i = 0; i < 3; i++) {
 196                                 if (d3 & c)
 197                                         bit |= b;
 198                                 c >>= 2;
 199                                 b >>= 1;
 200                         }
 201                         b = 0x01;
 202                         a = dat[add];
 203                         a ^= (b << bit);
 204                         dat[add] = a;
 205                         return 1;
 206                 } else {
 207                         i = 0;
 208                         while (d1) {
 209                                 if (d1 & 0x01)
 210                                         ++i;
 211                                 d1 >>= 1;
 212                         }
 213                         while (d2) {
 214                                 if (d2 & 0x01)
 215                                         ++i;
 216                                 d2 >>= 1;
 217                         }
 218                         while (d3) {
 219                                 if (d3 & 0x01)
 220                                         ++i;
 221                                 d3 >>= 1;
 222                         }
 223                         if (i == 1) {
 224                                 /* ECC Code Error Correction */
 225                                 read_ecc[0] = calc_ecc[0];
 226                                 read_ecc[1] = calc_ecc[1];
 227                                 read_ecc[2] = calc_ecc[2];
 228                                 return 2;
 229                         } else {
 230                                 /* Uncorrectable Error */
 231                                 return -1;
 232                         }
 233                 }
 234         }
 235
 236         /* Should never happen */
 237         return -1;
 238 }
 239
 240 EXPORT_SYMBOL(nand_calculate_ecc);
 241 EXPORT_SYMBOL(nand_correct_data);
 242
 243 MODULE_LICENSE("GPL");
 244 MODULE_AUTHOR("Steven J. Hill <sjhill@realitydiluted.com>");
 245 MODULE_DESCRIPTION("Generic NAND ECC support");