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  * Copyright (C) 2006 Thomas Gleixner <tglx@linutronix.de>
  11  *
  12  * $Id: nand_ecc.c,v 1.15 2005/11/07 11:14:30 gleixner Exp $
  13  *
  14  * This file is free software; you can redistribute it and/or modify it
  15  * under the terms of the GNU General Public License as published by the
  16  * Free Software Foundation; either version 2 or (at your option) any
  17  * later version.
  18  *
  19  * This file is distributed in the hope that it will be useful, but WITHOUT
  20  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  21  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  22  * for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License along
  25  * with this file; if not, write to the Free Software Foundation, Inc.,
  26  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  27  *
  28  * As a special exception, if other files instantiate templates or use
  29  * macros or inline functions from these files, or you compile these
  30  * files and link them with other works to produce a work based on these
  31  * files, these files do not by themselves cause the resulting work to be
  32  * covered by the GNU General Public License. However the source code for
  33  * these files must still be made available in accordance with section (3)
  34  * of the GNU General Public License.
  35  *
  36  * This exception does not invalidate any other reasons why a work based on
  37  * this file might be covered by the GNU General Public License.
  38  */
  39
  40 #include <linux/types.h>
  41 #include <linux/kernel.h>
  42 #include <linux/module.h>
  43 #include <linux/mtd/nand_ecc.h>
  44
  45 /*
  46  * Pre-calculated 256-way 1 byte column parity
  47  */
  48 static const u_char nand_ecc_precalc_table[] = {
  49         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
  50         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  51         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  52         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  53         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  54         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  55         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  56         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  57         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  58         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  59         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  60         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  61         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  62         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  63         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  64         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
  65 };
  66
  67 /**
  68  * nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256-byte block
  69  * @mtd:        MTD block structure
  70  * @dat:        raw data
  71  * @ecc_code:   buffer for ECC
  72  */
  73 int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
  74                        u_char *ecc_code)
  75 {
  76         uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
  77         int i;
  78
  79         /* Initialize variables */
  80         reg1 = reg2 = reg3 = 0;
  81
  82         /* Build up column parity */
  83         for(i = 0; i < 256; i++) {
  84                 /* Get CP0 - CP5 from table */
  85                 idx = nand_ecc_precalc_table[*dat++];
  86                 reg1 ^= (idx & 0x3f);
  87
  88                 /* All bit XOR = 1 ? */
  89                 if (idx & 0x40) {
  90                         reg3 ^= (uint8_t) i;
  91                         reg2 ^= ~((uint8_t) i);
  92                 }
  93         }
  94
  95         /* Create non-inverted ECC code from line parity */
  96         tmp1  = (reg3 & 0x80) >> 0; /* B7 -> B7 */
  97         tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */
  98         tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */
  99         tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */
 100         tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */
 101         tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */
 102         tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */
 103         tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */
 104
 105         tmp2  = (reg3 & 0x08) << 4; /* B3 -> B7 */
 106         tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */
 107         tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */
 108         tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */
 109         tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */
 110         tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */
 111         tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */
 112         tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */
 113
 114         /* Calculate final ECC code */
 115 #ifdef CONFIG_MTD_NAND_ECC_SMC
 116         ecc_code[0] = ~tmp2;
 117         ecc_code[1] = ~tmp1;
 118 #else
 119         ecc_code[0] = ~tmp1;
 120         ecc_code[1] = ~tmp2;
 121 #endif
 122         ecc_code[2] = ((~reg1) << 2) | 0x03;
 123
 124         return 0;
 125 }
 126 EXPORT_SYMBOL(nand_calculate_ecc);
 127
 128 static inline int countbits(uint32_t byte)
 129 {
 130         int res = 0;
 131
 132         for (;byte; byte >>= 1)
 133                 res += byte & 0x01;
 134         return res;
 135 }
 136
 137 /**
 138  * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
 139  * @mtd:        MTD block structure
 140  * @dat:        raw data read from the chip
 141  * @read_ecc:   ECC from the chip
 142  * @calc_ecc:   the ECC calculated from raw data
 143  *
 144  * Detect and correct a 1 bit error for 256 byte block
 145  */
 146 int nand_correct_data(struct mtd_info *mtd, u_char *dat,
 147                       u_char *read_ecc, u_char *calc_ecc)
 148 {
 149         uint8_t s0, s1, s2;
 150
 151 #ifdef CONFIG_MTD_NAND_ECC_SMC
 152         s0 = calc_ecc[0] ^ read_ecc[0];
 153         s1 = calc_ecc[1] ^ read_ecc[1];
 154         s2 = calc_ecc[2] ^ read_ecc[2];
 155 #else
 156         s1 = calc_ecc[0] ^ read_ecc[0];
 157         s0 = calc_ecc[1] ^ read_ecc[1];
 158         s2 = calc_ecc[2] ^ read_ecc[2];
 159 #endif
 160         if ((s0 | s1 | s2) == 0)
 161                 return 0;
 162
 163         /* Check for a single bit error */
 164         if( ((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
 165             ((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
 166             ((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {
 167
 168                 uint32_t byteoffs, bitnum;
 169
 170                 byteoffs = (s1 << 0) & 0x80;
 171                 byteoffs |= (s1 << 1) & 0x40;
 172                 byteoffs |= (s1 << 2) & 0x20;
 173                 byteoffs |= (s1 << 3) & 0x10;
 174
 175                 byteoffs |= (s0 >> 4) & 0x08;
 176                 byteoffs |= (s0 >> 3) & 0x04;
 177                 byteoffs |= (s0 >> 2) & 0x02;
 178                 byteoffs |= (s0 >> 1) & 0x01;
 179
 180                 bitnum = (s2 >> 5) & 0x04;
 181                 bitnum |= (s2 >> 4) & 0x02;
 182                 bitnum |= (s2 >> 3) & 0x01;
 183
 184                 dat[byteoffs] ^= (1 << bitnum);
 185
 186                 return 1;
 187         }
 188
 189         if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1)
 190                 return 1;
 191
 192         return -1;
 193 }
 194 EXPORT_SYMBOL(nand_correct_data);
 195
 196 MODULE_LICENSE("GPL");
 197 MODULE_AUTHOR("Steven J. Hill <sjhill@realitydiluted.com>");
 198 MODULE_DESCRIPTION("Generic NAND ECC support");