/*
* This file contains an ECC algorithm that detects and corrects 1 bit
* errors in a 256 byte block of data.
*
* drivers/mtd/nand/nand_ecc.c
*
* Copyright © 2008 Koninklijke Philips Electronics NV.
* Author: Frans Meulenbroeks
*
* Completely replaces the previous ECC implementation which was written by:
* Steven J. Hill (sjhill@realitydiluted.com)
* Thomas Gleixner (tglx@linutronix.de)
*
* Information on how this algorithm works and how it was developed
* can be found in Documentation/mtd/nand_ecc.txt
*
* This file is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 or (at your option) any
* later version.
*
* This file is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this file; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*
*/
/*
* The STANDALONE macro is useful when running the code outside the kernel
* e.g. when running the code in a testbed or a benchmark program.
* When STANDALONE is used, the module related macros are commented out
* as well as the linux include files.
* Instead a private definition of mtd_info is given to satisfy the compiler
* (the code does not use mtd_info, so the code does not care)
*/
#ifndef STANDALONE
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_ecc.h>
#include <asm/byteorder.h>
#else
#include <stdint.h>
struct mtd_info;
#define EXPORT_SYMBOL(x) /* x */
#define MODULE_LICENSE(x) /* x */
#define MODULE_AUTHOR(x) /* x */
#define MODULE_DESCRIPTION(x) /* x */
#define printk printf
#define KERN_ERR ""
#endif
/*
* invparity is a 256 byte table that contains the odd parity
* for each byte. So if the number of bits in a byte is even,
* the array element is 1, and when the number of bits is odd
* the array eleemnt is 0.
*/
static const char invparity[256] = {
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1
};
/*
* bitsperbyte contains the number of bits per byte
* this is only used for testing and repairing parity
* (a precalculated value slightly improves performance)
*/
static const char bitsperbyte[256] = {
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
};
/*
* addressbits is a lookup table to filter out the bits from the xor-ed
* ecc data that identify the faulty location.
* this is only used for repairing parity
* see the comments in nand_correct_data for more details
*/
static const char addressbits[256] = {
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f
};
/**
* nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
* block
* @mtd: MTD block structure
* @buf: input buffer with raw data
* @code: output buffer with ECC
*/
int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
unsigned char *code)
{
int i;
const uint32_t *bp = (uint32_t *)buf;
/* 256 or 512 bytes/ecc */
const uint32_t eccsize_mult =
(((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
uint32_t cur; /* current value in buffer */
/* rp0..rp15..rp17 are the various accumulated parities (per byte) */
uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
uint32_t uninitialized_var(rp17); /* to make compiler happy */
uint32_t par; /* the cumulative parity for all data */
uint32_t tmppar; /* the cumulative parity for this iteration;
for rp12, rp14 and rp16 at the end of the
loop */
par = 0;
rp4 = 0;
rp6 = 0;
rp8 = 0;
rp10 = 0;
rp12 = 0;
rp14 = 0;
rp16 = 0;
/*
* The loop is unrolled a number of times;
* This avoids if statements to decide on which rp value to update
* Also we process the data by longwords.
* Note: passing unaligned data might give a performance penalty.
* It is assumed that the buffers are aligned.
* tmppar is the cumulative sum of this iteration.
* needed for calculating rp12, rp14, rp16 and par
* also used as a performance improvement for rp6, rp8 and rp10
*/
for (i = 0; i < eccsize_mult << 2; i++) {
cur = *bp++;
tmppar = cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp8 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp10 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
par ^= tmppar;
if ((i & 0x1) == 0)
rp12 ^= tmppar;
if ((i & 0x2) == 0)
rp14 ^= tmppar;
if (eccsize_mult == 2 && (i & 0x4) == 0)
rp16 ^= tmppar;
}
/*
* handle the fact that we use longword operations
* we'll bring rp4..rp14..rp16 back to single byte entities by
* shifting and xoring first fold the upper and lower 16 bits,
* then the upper and lower 8 bits.
*/
rp4 ^= (rp4 >> 16);
rp4 ^= (rp4 >> 8);
rp4 &= 0xff;
rp6 ^= (rp6 >> 16);
rp6 ^= (rp6 >> 8);
rp6 &= 0xff;
rp8 ^= (rp8 >> 16);
rp8 ^= (rp8 >> 8);
rp8 &= 0xff;
rp10 ^= (rp10 >> 16);
rp10 ^= (rp10 >> 8);
rp10 &= 0xff;
rp12 ^= (rp12 >> 16);
rp12 ^= (rp12 >> 8);
rp12 &= 0xff;
rp14 ^= (rp14 >> 16);
rp14 ^= (rp14 >> 8);
rp14 &= 0xff;
if (eccsize_mult == 2) {
rp16 ^= (rp16 >> 16);
rp16 ^= (rp16 >> 8);
rp16 &= 0xff;
}
/*
* we also need to calculate the row parity for rp0..rp3
* This is present in par, because par is now
* rp3 rp3 rp2 rp2 in little endian and
* rp2 rp2 rp3 rp3 in big endian
* as well as
* rp1 rp0 rp1 rp0 in little endian and
* rp0 rp1 rp0 rp1 in big endian
* First calculate rp2 and rp3
*/
#ifdef __BIG_ENDIAN
rp2 = (par >> 16);
rp2 ^= (rp2 >> 8);
rp2 &= 0xff;
rp3 = par & 0xffff;
rp3 ^= (rp3 >> 8);
rp3 &= 0xff;
#else
rp3 = (par >> 16);
rp3 ^= (rp3 >> 8);
rp3 &= 0xff;
rp2 = par & 0xffff;
rp2 ^= (rp2 >> 8);
rp2 &= 0xff;
#endif
/* reduce par to 16 bits then calculate rp1 and rp0 */
par ^= (par >> 16);
#ifdef __BIG_ENDIAN
rp0 = (par >> 8) & 0xff;
rp1 = (par & 0xff);
#else
rp1 = (par >> 8) & 0xff;
rp0 = (par & 0xff);
#endif
/* finally reduce par to 8 bits */
par ^= (par >> 8);
par &= 0xff;
/*
* and calculate rp5..rp15..rp17
* note that par = rp4 ^ rp5 and due to the commutative property
* of the ^ operator we can say:
* rp5 = (par ^ rp4);
* The & 0xff seems superfluous, but benchmarking learned that
* leaving it out gives slightly worse results. No idea why, probably
* it has to do with the way the pipeline in pentium is organized.
*/
rp5 = (par ^ rp4) & 0xff;
rp7 = (par ^ rp6) & 0xff;
rp9 = (par ^ rp8) & 0xff;
rp11 = (par ^ rp10) & 0xff;
rp13 = (par ^ rp12) & 0xff;
rp15 = (par ^ rp14) & 0xff;
if (eccsize_mult == 2)
rp17 = (par ^ rp16) & 0xff;
/*
* Finally calculate the ecc bits.
* Again here it might seem that there are performance optimisations
* possible, but benchmarks showed that on the system this is developed
* the code below is the fastest
*/
#ifdef CONFIG_MTD_NAND_ECC_SMC
code[0] =
(invparity[rp7] << 7) |
(invparity[rp6] << 6) |
(invparity[rp5] << 5) |
(invparity[rp4] << 4) |
(invparity[rp3] << 3) |
(invparity[rp2] << 2) |
(invparity[rp1] << 1) |
(invparity[rp0]);
code[1] =
(invparity[rp15] << 7) |
(invparity[rp14] << 6) |
(invparity[rp13] << 5) |
(invparity[rp12] << 4) |
(invparity[rp11] << 3) |
(invparity[rp10] << 2) |
(invparity[rp9] << 1) |
(invparity[rp8]);
#else
code[1] =
(invparity[rp7] << 7) |
(invparity[rp6] << 6) |
(invparity[rp5] << 5) |
(invparity[rp4] << 4) |
(invparity[rp3] << 3) |
(invparity[rp2] << 2) |
(invparity[rp1] << 1) |
(invparity[rp0]);
code[0] =
(invparity[rp15] << 7) |
(invparity[rp14] << 6) |
(invparity[rp13] << 5) |
(invparity[rp12] << 4) |
(invparity[rp11] << 3) |
(invparity[rp10] << 2) |
(invparity[rp9] << 1) |
(invparity[rp8]);
#endif
if (eccsize_mult == 1)
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
3;
else
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
(invparity[rp17] << 1) |
(invparity[rp16] << 0);
return 0;
}
EXPORT_SYMBOL(nand_calculate_ecc);
/**
* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
* @mtd: MTD block structure
* @buf: raw data read from the chip
* @read_ecc: ECC from the chip
* @calc_ecc: the ECC calculated from raw data
*
* Detect and correct a 1 bit error for 256/512 byte block
*/
int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
unsigned char *read_ecc, unsigned char *calc_ecc)
{
unsigned char b0, b1, b2;
unsigned char byte_addr, bit_addr;
/* 256 or 512 bytes/ecc */
const uint32_t eccsize_mult =
(((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
/*
* b0 to b2 indicate which bit is faulty (if any)
* we might need the xor result more than once,
* so keep them in a local var
*/
#ifdef CONFIG_MTD_NAND_ECC_SMC
b0 = read_ecc[0] ^ calc_ecc[0];
b1 = read_ecc[1] ^ calc_ecc[1];
#else
b0 = read_ecc[1] ^ calc_ecc[1];
b1 = read_ecc[0] ^ calc_ecc[0];
#endif
b2 = read_ecc[2] ^ calc_ecc[2];
/* check if there are any bitfaults */
/* repeated if statements are slightly more efficient than switch ... */
/* ordered in order of likelihood */
if ((b0 | b1 | b2) == 0)
return 0; /* no error */
if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
(((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
(eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
/* single bit error */
/*
* rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
* byte, cp 5/3/1 indicate the faulty bit.
* A lookup table (called addressbits) is used to filter
* the bits from the byte they are in.
* A marginal optimisation is possible by having three
* different lookup tables.
* One as we have now (for b0), one for b2
* (that would avoid the >> 1), and one for b1 (with all values
* << 4). However it was felt that introducing two more tables
* hardly justify the gain.
*
* The b2 shift is there to get rid of the lowest two bits.
* We could also do addressbits[b2] >> 1 but for the
* performace it does not make any difference
*/
if (eccsize_mult == 1)
byte_addr = (addressbits[b1] << 4) + addressbits[b0];
else
byte_addr = (addressbits[b2 & 0x3] << 8) +
(addressbits[b1] << 4) + addressbits[b0];
bit_addr = addressbits[b2 >> 2];
/* flip the bit */
buf[byte_addr] ^= (1 << bit_addr);
return 1;
}
/* count nr of bits; use table lookup, faster than calculating it */
if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
return 1; /* error in ecc data; no action needed */
printk(KERN_ERR "uncorrectable error : ");
return -1;
}
EXPORT_SYMBOL(nand_correct_data);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
MODULE_DESCRIPTION("Generic NAND ECC support");
