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提交 e6cf5df1 编写于 作者: F frans 提交者： David Woodhouse
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[MTD] [NAND] nand_ecc.c: rewrite for improved performance 

This patch improves the performance of the ecc generation code by a 
factor of 18 on an INTEL D920 CPU, a factor of 7 on MIPS and a factor of 5 
on ARM (NSLU2)
Signed-off-by: NFrans Meulenbroeks <fransmeulenbroeks@gmail.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>
上级 782b7a36
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Documentation/mtd/nand_ecc.txt 0 → 100644
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drivers/mtd/nand/nand_ecc.c
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/* /*
* This file contains an ECC algorithm from Toshiba that detects and * This file contains an ECC algorithm that detects and corrects 1 bit
* corrects 1 bit errors in a 256 byte block of data. * errors in a 256 byte block of data.
* *
* drivers/mtd/nand/nand_ecc.c * drivers/mtd/nand/nand_ecc.c
* *
* Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com) * Copyright (C) 2008 Koninklijke Philips Electronics NV.
* Toshiba America Electronics Components, Inc. * Author: Frans Meulenbroeks
* *
* Copyright (C) 2006 Thomas Gleixner <tglx@linutronix.de> * 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/nand/ecc.txt
* *
* This file is free software; you can redistribute it and/or modify it * 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 * under the terms of the GNU General Public License as published by the
...@@ -23,174 +28,417 @@ ...@@ -23,174 +28,417 @@
* with this file; if not, write to the Free Software Foundation, Inc., * with this file; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
* *
* As a special exception, if other files instantiate templates or use
* macros or inline functions from these files, or you compile these
* files and link them with other works to produce a work based on these
* files, these files do not by themselves cause the resulting work to be
* covered by the GNU General Public License. However the source code for
* these files must still be made available in accordance with section (3)
* of the GNU General Public License.
*
* This exception does not invalidate any other reasons why a work based on
* this file might be covered by the GNU General Public License.
*/ */
/*
* 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_into 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/types.h>
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/mtd/nand_ecc.h> #include <linux/mtd/nand_ecc.h>
#else
typedef uint32_t unsigned long
struct mtd_info {
int dummy;
};
#define EXPORT_SYMBOL(x) /* x */
#define MODULE_LICENSE(x) /* x */
#define MODULE_AUTHOR(x) /* x */
#define MODULE_DESCRIPTION(x) /* x */
#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
};
/* /*
* Pre-calculated 256-way 1 byte column parity * 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 u_char nand_ecc_precalc_table[] = { static const char bitsperbyte[256] = {
0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00, 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00 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-byte block * nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256-byte block
* @mtd: MTD block structure * @mtd: MTD block structure (unused)
* @dat: raw data * @dat: raw data
* @ecc_code: buffer for ECC * @ecc_code: buffer for ECC
*/ */
int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
u_char *ecc_code) unsigned char *code)
{ {
uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
int i; int i;
const uint32_t *bp = (uint32_t *)buf;
uint32_t cur; /* current value in buffer */
/* rp0..rp15 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;
uint32_t par; /* the cumulative parity for all data */
uint32_t tmppar; /* the cumulative parity for this iteration;
for rp12 and rp14 at the end of the loop */
par = 0;
rp4 = 0;
rp6 = 0;
rp8 = 0;
rp10 = 0;
rp12 = 0;
rp14 = 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 and par
* also used as a performance improvement for rp6, rp8 and rp10
*/
for (i = 0; i < 4; 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;
/* Initialize variables */ cur = *bp++;
reg1 = reg2 = reg3 = 0; tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp10 ^= tmppar;
/* Build up column parity */ cur = *bp++;
for(i = 0; i < 256; i++) { tmppar ^= cur;
/* Get CP0 - CP5 from table */ rp4 ^= cur;
idx = nand_ecc_precalc_table[*dat++]; rp6 ^= cur;
reg1 ^= (idx & 0x3f); rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp8 ^= cur;
/* All bit XOR = 1 ? */ cur = *bp++;
if (idx & 0x40) { tmppar ^= cur;
reg3 ^= (uint8_t) i; rp4 ^= cur;
reg2 ^= ~((uint8_t) i); 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;
} }
/* Create non-inverted ECC code from line parity */ /*
tmp1 = (reg3 & 0x80) >> 0; /* B7 -> B7 */ * handle the fact that we use longword operations
tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */ * we'll bring rp4..rp14 back to single byte entities by shifting and
tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */ * xoring first fold the upper and lower 16 bits,
tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */ * then the upper and lower 8 bits.
tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */ */
tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */ rp4 ^= (rp4 >> 16);
tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */ rp4 ^= (rp4 >> 8);
tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */ rp4 &= 0xff;
rp6 ^= (rp6 >> 16);
tmp2 = (reg3 & 0x08) << 4; /* B3 -> B7 */ rp6 ^= (rp6 >> 8);
tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */ rp6 &= 0xff;
tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */ rp8 ^= (rp8 >> 16);
tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */ rp8 ^= (rp8 >> 8);
tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */ rp8 &= 0xff;
tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */ rp10 ^= (rp10 >> 16);
tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */ rp10 ^= (rp10 >> 8);
tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */ rp10 &= 0xff;
rp12 ^= (rp12 >> 16);
/* Calculate final ECC code */ rp12 ^= (rp12 >> 8);
rp12 &= 0xff;
rp14 ^= (rp14 >> 16);
rp14 ^= (rp14 >> 8);
rp14 &= 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
* as well as
* rp1 rp0 rp1 rp0
* First calculate rp2 and rp3
* (and yes: rp2 = (par ^ rp3) & 0xff; but doing that did not
* give a performance improvement)
*/
rp3 = (par >> 16);
rp3 ^= (rp3 >> 8);
rp3 &= 0xff;
rp2 = par & 0xffff;
rp2 ^= (rp2 >> 8);
rp2 &= 0xff;
/* reduce par to 16 bits then calculate rp1 and rp0 */
par ^= (par >> 16);
rp1 = (par >> 8) & 0xff;
rp0 = (par & 0xff);
/* finally reduce par to 8 bits */
par ^= (par >> 8);
par &= 0xff;
/*
* and calculate rp5..rp15
* 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;
/*
* 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 #ifdef CONFIG_MTD_NAND_ECC_SMC
ecc_code[0] = ~tmp2; code[0] =
ecc_code[1] = ~tmp1; (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 #else
ecc_code[0] = ~tmp1; code[1] =
ecc_code[1] = ~tmp2; (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 #endif
ecc_code[2] = ((~reg1) << 2) | 0x03; 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;
return 0; return 0;
} }
EXPORT_SYMBOL(nand_calculate_ecc); EXPORT_SYMBOL(nand_calculate_ecc);
static inline int countbits(uint32_t byte)
{
int res = 0;
for (;byte; byte >>= 1)
res += byte & 0x01;
return res;
}
/** /**
* nand_correct_data - [NAND Interface] Detect and correct bit error(s) * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
* @mtd: MTD block structure * @mtd: MTD block structure (unused)
* @dat: raw data read from the chip * @dat: raw data read from the chip
* @read_ecc: ECC from the chip * @read_ecc: ECC from the chip
* @calc_ecc: the ECC calculated from raw data * @calc_ecc: the ECC calculated from raw data
* *
* Detect and correct a 1 bit error for 256 byte block * Detect and correct a 1 bit error for 256 byte block
*/ */
int nand_correct_data(struct mtd_info *mtd, u_char *dat, int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
u_char *read_ecc, u_char *calc_ecc) unsigned char *read_ecc, unsigned char *calc_ecc)
{ {
uint8_t s0, s1, s2; int nr_bits;
unsigned char b0, b1, b2;
unsigned char byte_addr, bit_addr;
/*
* 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 #ifdef CONFIG_MTD_NAND_ECC_SMC
s0 = calc_ecc[0] ^ read_ecc[0]; b0 = read_ecc[0] ^ calc_ecc[0];
s1 = calc_ecc[1] ^ read_ecc[1]; b1 = read_ecc[1] ^ calc_ecc[1];
s2 = calc_ecc[2] ^ read_ecc[2];
#else #else
s1 = calc_ecc[0] ^ read_ecc[0]; b0 = read_ecc[1] ^ calc_ecc[1];
s0 = calc_ecc[1] ^ read_ecc[1]; b1 = read_ecc[0] ^ calc_ecc[0];
s2 = calc_ecc[2] ^ read_ecc[2];
#endif #endif
if ((s0 | s1 | s2) == 0) b2 = read_ecc[2] ^ calc_ecc[2];
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; /* check if there are any bitfaults */
byteoffs |= (s1 << 1) & 0x40;
byteoffs |= (s1 << 2) & 0x20;
byteoffs |= (s1 << 3) & 0x10;
byteoffs |= (s0 >> 4) & 0x08; /* count nr of bits; use table lookup, faster than calculating it */
byteoffs |= (s0 >> 3) & 0x04; nr_bits = bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2];
byteoffs |= (s0 >> 2) & 0x02;
byteoffs |= (s0 >> 1) & 0x01;
bitnum = (s2 >> 5) & 0x04; /* repeated if statements are slightly more efficient than switch ... */
bitnum |= (s2 >> 4) & 0x02; /* ordered in order of likelihood */
bitnum |= (s2 >> 3) & 0x01; if (nr_bits == 0)
return (0); /* no error */
dat[byteoffs] ^= (1 << bitnum); if (nr_bits == 11) { /* correctable error */
/*
return 1; * 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
*/
byte_addr = (addressbits[b1] << 4) + addressbits[b0];
bit_addr = addressbits[b2 >> 2];
/* flip the bit */
buf[byte_addr] ^= (1 << bit_addr);
return (1);
} }
if (nr_bits == 1)
if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1) return (1); /* error in ecc data; no action needed */
return 1; return -1;
return -EBADMSG;
} }
EXPORT_SYMBOL(nand_correct_data); EXPORT_SYMBOL(nand_correct_data);
MODULE_LICENSE("GPL"); MODULE_LICENSE("GPL");
MODULE_AUTHOR("Steven J. Hill <sjhill@realitydiluted.com>"); MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
MODULE_DESCRIPTION("Generic NAND ECC support"); MODULE_DESCRIPTION("Generic NAND ECC support");
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