ecc.c

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// SPDX-License-Identifier: GPL-2.0-or-later WITH eCos-exception-2.0
 
/*
 * This file contains an ECC algorithm from Toshiba that allows for detection
 * and correction of 1-bit errors in a 256 byte block of data.
 *
 * [ Extracted from the initial code found in some early Linux versions.
 *   The current Linux code is bigger while being faster, but this is of
 *   no real benefit when the bottleneck largely remains the JTAG link.  ]
 *
 * Copyright (C) 2000-2004 Steven J. Hill (sjhill at realitydiluted.com)
 *                         Toshiba America Electronics Components, Inc.
 *
 * Copyright (C) 2006 Thomas Gleixner <tglx at linutronix.de>
 */
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include "core.h"
 
/*
 * Pre-calculated 256-way 1 byte column parity
 */
static const uint8_t nand_ecc_precalc_table[] = {
    0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
    0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
    0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
    0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
    0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
    0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
    0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
    0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
    0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
    0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
    0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
    0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
    0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
    0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
    0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
    0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
};
 
/*
 * nand_calculate_ecc - Calculate 3-byte ECC for 256-byte block
 */
int nand_calculate_ecc(struct nand_device *nand, const uint8_t *dat, uint8_t *ecc_code)
{
    uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
    int i;
 
    /* Initialize variables */
    reg1 = reg2 = reg3 = 0;
 
    /* Build up column parity */
    for (i = 0; i < 256; i++) {
        /* Get CP0 - CP5 from table */
        idx = nand_ecc_precalc_table[*dat++];
        reg1 ^= (idx & 0x3f);
 
        /* All bit XOR = 1 ? */
        if (idx & 0x40) {
            reg3 ^= (uint8_t) i;
            reg2 ^= ~((uint8_t) i);
        }
    }
 
    /* Create non-inverted ECC code from line parity */
    tmp1  = (reg3 & 0x80) >> 0; /* B7 -> B7 */
    tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */
    tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */
    tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */
    tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */
    tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */
    tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */
    tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */
 
    tmp2  = (reg3 & 0x08) << 4; /* B3 -> B7 */
    tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */
    tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */
    tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */
    tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */
    tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */
    tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */
    tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */
 
    /* Calculate final ECC code */
#ifdef NAND_ECC_SMC
    ecc_code[0] = ~tmp2;
    ecc_code[1] = ~tmp1;
#else
    ecc_code[0] = ~tmp1;
    ecc_code[1] = ~tmp2;
#endif
    ecc_code[2] = ((~reg1) << 2) | 0x03;
 
    return 0;
}
 
static inline int countbits(uint32_t b)
{
    int res = 0;
 
    for (; b; b >>= 1)
        res += b & 0x01;
    return res;
}
 
int nand_correct_data(struct nand_device *nand, u_char *dat,
        u_char *read_ecc, u_char *calc_ecc)
{
    uint8_t s0, s1, s2;
 
#ifdef NAND_ECC_SMC
    s0 = calc_ecc[0] ^ read_ecc[0];
    s1 = calc_ecc[1] ^ read_ecc[1];
    s2 = calc_ecc[2] ^ read_ecc[2];
#else
    s1 = calc_ecc[0] ^ read_ecc[0];
    s0 = calc_ecc[1] ^ read_ecc[1];
    s2 = calc_ecc[2] ^ read_ecc[2];
#endif
    if ((s0 | s1 | s2) == 0)
        return 0;
 
    /* Check for a single bit error */
    if (((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
            ((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
            ((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {
 
        uint32_t byteoffs, bitnum;
 
        byteoffs = (s1 << 0) & 0x80;
        byteoffs |= (s1 << 1) & 0x40;
        byteoffs |= (s1 << 2) & 0x20;
        byteoffs |= (s1 << 3) & 0x10;
 
        byteoffs |= (s0 >> 4) & 0x08;
        byteoffs |= (s0 >> 3) & 0x04;
        byteoffs |= (s0 >> 2) & 0x02;
        byteoffs |= (s0 >> 1) & 0x01;
 
        bitnum = (s2 >> 5) & 0x04;
        bitnum |= (s2 >> 4) & 0x02;
        bitnum |= (s2 >> 3) & 0x01;
 
        dat[byteoffs] ^= (1 << bitnum);
 
        return 1;
    }
 
    if (countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 << 16)) == 1)
        return 1;
 
    return -1;
}