[MTD] Improve software ECC calculation

Unrolling the loops produces denser and much faster code.
Add a config switch which allows to select the byte order of the
resulting ecc code. The current Linux implementation has a byte
swap versus the SmartMedia specification

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2006-05-23 11:32:45 +02:00
parent a1b563d652
commit 819d6a32c3
2 changed files with 95 additions and 133 deletions

View File

@ -23,6 +23,14 @@ config MTD_NAND_VERIFY_WRITE
device thinks the write was successful, a bit could have been
flipped accidentaly due to device wear or something else.
config MTD_NAND_ECC_SMC
bool "NAND ECC Smart Media byte order"
depends on MTD_NAND
default n
help
Software ECC according to the Smart Media Specification.
The original Linux implementation had byte 0 and 1 swapped.
config MTD_NAND_AUTCPU12
tristate "SmartMediaCard on autronix autcpu12 board"
depends on MTD_NAND && ARCH_AUTCPU12

View File

@ -7,6 +7,8 @@
* Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
* Toshiba America Electronics Components, Inc.
*
* Copyright (C) 2006 Thomas Gleixner <tglx@linutronix.de>
*
* $Id: nand_ecc.c,v 1.15 2005/11/07 11:14:30 gleixner Exp $
*
* This file is free software; you can redistribute it and/or modify it
@ -63,87 +65,75 @@ static const u_char nand_ecc_precalc_table[] = {
};
/**
* nand_trans_result - [GENERIC] create non-inverted ECC
* @reg2: line parity reg 2
* @reg3: line parity reg 3
* @ecc_code: ecc
*
* Creates non-inverted ECC code from line parity
*/
static void nand_trans_result(u_char reg2, u_char reg3, u_char *ecc_code)
{
u_char a, b, i, tmp1, tmp2;
/* Initialize variables */
a = b = 0x80;
tmp1 = tmp2 = 0;
/* Calculate first ECC byte */
for (i = 0; i < 4; i++) {
if (reg3 & a) /* LP15,13,11,9 --> ecc_code[0] */
tmp1 |= b;
b >>= 1;
if (reg2 & a) /* LP14,12,10,8 --> ecc_code[0] */
tmp1 |= b;
b >>= 1;
a >>= 1;
}
/* Calculate second ECC byte */
b = 0x80;
for (i = 0; i < 4; i++) {
if (reg3 & a) /* LP7,5,3,1 --> ecc_code[1] */
tmp2 |= b;
b >>= 1;
if (reg2 & a) /* LP6,4,2,0 --> ecc_code[1] */
tmp2 |= b;
b >>= 1;
a >>= 1;
}
/* Store two of the ECC bytes */
ecc_code[0] = tmp1;
ecc_code[1] = tmp2;
}
/**
* nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
* nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code
* for 256 byte block
* @mtd: MTD block structure
* @dat: raw data
* @ecc_code: buffer for ECC
*/
int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
u_char *ecc_code)
{
u_char idx, reg1, reg2, reg3;
int j;
uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
int i;
/* Initialize variables */
reg1 = reg2 = reg3 = 0;
ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
/* Build up column parity */
for (j = 0; j < 256; j++) {
for(i = 0; i < 256; i++) {
/* Get CP0 - CP5 from table */
idx = nand_ecc_precalc_table[dat[j]];
idx = nand_ecc_precalc_table[*dat++];
reg1 ^= (idx & 0x3f);
/* All bit XOR = 1 ? */
if (idx & 0x40) {
reg3 ^= (u_char) j;
reg2 ^= ~((u_char) j);
reg3 ^= (uint8_t) i;
reg2 ^= ~((uint8_t) i);
}
}
/* Create non-inverted ECC code from line parity */
nand_trans_result(reg2, reg3, ecc_code);
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 */
ecc_code[0] = ~ecc_code[0];
ecc_code[1] = ~ecc_code[1];
#ifdef CONFIG_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;
}
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)
@ -154,90 +144,54 @@ int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code
*
* Detect and correct a 1 bit error for 256 byte block
*/
int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
int nand_correct_data(struct mtd_info *mtd, u_char *dat,
u_char *read_ecc, u_char *calc_ecc)
{
u_char a, b, c, d1, d2, d3, add, bit, i;
uint8_t s0, s1, s2;
/* Do error detection */
d1 = calc_ecc[0] ^ read_ecc[0];
d2 = calc_ecc[1] ^ read_ecc[1];
d3 = calc_ecc[2] ^ read_ecc[2];
if ((d1 | d2 | d3) == 0) {
/* No errors */
#ifdef CONFIG_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;
} else {
a = (d1 ^ (d1 >> 1)) & 0x55;
b = (d2 ^ (d2 >> 1)) & 0x55;
c = (d3 ^ (d3 >> 1)) & 0x54;
/* Found and will correct single bit error in the data */
if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
c = 0x80;
add = 0;
a = 0x80;
for (i = 0; i < 4; i++) {
if (d1 & c)
add |= a;
c >>= 2;
a >>= 1;
}
c = 0x80;
for (i = 0; i < 4; i++) {
if (d2 & c)
add |= a;
c >>= 2;
a >>= 1;
}
bit = 0;
b = 0x04;
c = 0x80;
for (i = 0; i < 3; i++) {
if (d3 & c)
bit |= b;
c >>= 2;
b >>= 1;
}
b = 0x01;
a = dat[add];
a ^= (b << bit);
dat[add] = a;
return 1;
} else {
i = 0;
while (d1) {
if (d1 & 0x01)
++i;
d1 >>= 1;
}
while (d2) {
if (d2 & 0x01)
++i;
d2 >>= 1;
}
while (d3) {
if (d3 & 0x01)
++i;
d3 >>= 1;
}
if (i == 1) {
/* ECC Code Error Correction */
read_ecc[0] = calc_ecc[0];
read_ecc[1] = calc_ecc[1];
read_ecc[2] = calc_ecc[2];
return 2;
} else {
/* Uncorrectable Error */
return -1;
}
}
/* 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;
}
/* Should never happen */
if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1)
return 1;
return -1;
}
EXPORT_SYMBOL(nand_calculate_ecc);
EXPORT_SYMBOL(nand_correct_data);
MODULE_LICENSE("GPL");