[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
parent
a1b563d652
commit
819d6a32c3
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@ -23,6 +23,14 @@ config MTD_NAND_VERIFY_WRITE
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device thinks the write was successful, a bit could have been
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flipped accidentaly due to device wear or something else.
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config MTD_NAND_ECC_SMC
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bool "NAND ECC Smart Media byte order"
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depends on MTD_NAND
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default n
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help
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Software ECC according to the Smart Media Specification.
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The original Linux implementation had byte 0 and 1 swapped.
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config MTD_NAND_AUTCPU12
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tristate "SmartMediaCard on autronix autcpu12 board"
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depends on MTD_NAND && ARCH_AUTCPU12
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@ -7,6 +7,8 @@
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* Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
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* Toshiba America Electronics Components, Inc.
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*
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* Copyright (C) 2006 Thomas Gleixner <tglx@linutronix.de>
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*
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* $Id: nand_ecc.c,v 1.15 2005/11/07 11:14:30 gleixner Exp $
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*
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* This file is free software; you can redistribute it and/or modify it
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@ -63,87 +65,75 @@ static const u_char nand_ecc_precalc_table[] = {
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};
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/**
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* nand_trans_result - [GENERIC] create non-inverted ECC
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* @reg2: line parity reg 2
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* @reg3: line parity reg 3
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* @ecc_code: ecc
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*
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* Creates non-inverted ECC code from line parity
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*/
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static void nand_trans_result(u_char reg2, u_char reg3, u_char *ecc_code)
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{
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u_char a, b, i, tmp1, tmp2;
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/* Initialize variables */
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a = b = 0x80;
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tmp1 = tmp2 = 0;
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/* Calculate first ECC byte */
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for (i = 0; i < 4; i++) {
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if (reg3 & a) /* LP15,13,11,9 --> ecc_code[0] */
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tmp1 |= b;
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b >>= 1;
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if (reg2 & a) /* LP14,12,10,8 --> ecc_code[0] */
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tmp1 |= b;
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b >>= 1;
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a >>= 1;
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}
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/* Calculate second ECC byte */
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b = 0x80;
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for (i = 0; i < 4; i++) {
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if (reg3 & a) /* LP7,5,3,1 --> ecc_code[1] */
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tmp2 |= b;
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b >>= 1;
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if (reg2 & a) /* LP6,4,2,0 --> ecc_code[1] */
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tmp2 |= b;
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b >>= 1;
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a >>= 1;
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}
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/* Store two of the ECC bytes */
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ecc_code[0] = tmp1;
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ecc_code[1] = tmp2;
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}
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/**
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* nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
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* nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code
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* for 256 byte block
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* @mtd: MTD block structure
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* @dat: raw data
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* @ecc_code: buffer for ECC
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*/
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int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
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int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
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u_char *ecc_code)
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{
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u_char idx, reg1, reg2, reg3;
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int j;
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uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
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int i;
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/* Initialize variables */
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reg1 = reg2 = reg3 = 0;
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ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
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/* Build up column parity */
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for (j = 0; j < 256; j++) {
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for(i = 0; i < 256; i++) {
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/* Get CP0 - CP5 from table */
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idx = nand_ecc_precalc_table[dat[j]];
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idx = nand_ecc_precalc_table[*dat++];
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reg1 ^= (idx & 0x3f);
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/* All bit XOR = 1 ? */
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if (idx & 0x40) {
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reg3 ^= (u_char) j;
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reg2 ^= ~((u_char) j);
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reg3 ^= (uint8_t) i;
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reg2 ^= ~((uint8_t) i);
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}
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}
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/* Create non-inverted ECC code from line parity */
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nand_trans_result(reg2, reg3, ecc_code);
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tmp1 = (reg3 & 0x80) >> 0; /* B7 -> B7 */
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tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */
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tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */
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tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */
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tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */
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tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */
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tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */
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tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */
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tmp2 = (reg3 & 0x08) << 4; /* B3 -> B7 */
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tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */
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tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */
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tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */
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tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */
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tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */
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tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */
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tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */
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/* Calculate final ECC code */
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ecc_code[0] = ~ecc_code[0];
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ecc_code[1] = ~ecc_code[1];
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#ifdef CONFIG_NAND_ECC_SMC
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ecc_code[0] = ~tmp2;
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ecc_code[1] = ~tmp1;
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#else
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ecc_code[0] = ~tmp1;
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ecc_code[1] = ~tmp2;
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#endif
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ecc_code[2] = ((~reg1) << 2) | 0x03;
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return 0;
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}
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EXPORT_SYMBOL(nand_calculate_ecc);
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static inline int countbits(uint32_t byte)
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{
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int res = 0;
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for (;byte; byte >>= 1)
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res += byte & 0x01;
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return res;
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}
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/**
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* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
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@ -154,90 +144,54 @@ int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code
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*
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* Detect and correct a 1 bit error for 256 byte block
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*/
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int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
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int nand_correct_data(struct mtd_info *mtd, u_char *dat,
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u_char *read_ecc, u_char *calc_ecc)
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{
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u_char a, b, c, d1, d2, d3, add, bit, i;
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uint8_t s0, s1, s2;
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/* Do error detection */
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d1 = calc_ecc[0] ^ read_ecc[0];
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d2 = calc_ecc[1] ^ read_ecc[1];
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d3 = calc_ecc[2] ^ read_ecc[2];
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if ((d1 | d2 | d3) == 0) {
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/* No errors */
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#ifdef CONFIG_NAND_ECC_SMC
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s0 = calc_ecc[0] ^ read_ecc[0];
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s1 = calc_ecc[1] ^ read_ecc[1];
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s2 = calc_ecc[2] ^ read_ecc[2];
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#else
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s1 = calc_ecc[0] ^ read_ecc[0];
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s0 = calc_ecc[1] ^ read_ecc[1];
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s2 = calc_ecc[2] ^ read_ecc[2];
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#endif
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if ((s0 | s1 | s2) == 0)
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return 0;
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} else {
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a = (d1 ^ (d1 >> 1)) & 0x55;
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b = (d2 ^ (d2 >> 1)) & 0x55;
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c = (d3 ^ (d3 >> 1)) & 0x54;
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/* Found and will correct single bit error in the data */
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if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
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c = 0x80;
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add = 0;
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a = 0x80;
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for (i = 0; i < 4; i++) {
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if (d1 & c)
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add |= a;
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c >>= 2;
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a >>= 1;
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}
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c = 0x80;
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for (i = 0; i < 4; i++) {
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if (d2 & c)
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add |= a;
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c >>= 2;
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a >>= 1;
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}
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bit = 0;
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b = 0x04;
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c = 0x80;
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for (i = 0; i < 3; i++) {
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if (d3 & c)
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bit |= b;
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c >>= 2;
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b >>= 1;
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}
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b = 0x01;
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a = dat[add];
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a ^= (b << bit);
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dat[add] = a;
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return 1;
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} else {
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i = 0;
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while (d1) {
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if (d1 & 0x01)
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++i;
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d1 >>= 1;
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}
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while (d2) {
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if (d2 & 0x01)
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++i;
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d2 >>= 1;
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}
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while (d3) {
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if (d3 & 0x01)
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++i;
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d3 >>= 1;
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}
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if (i == 1) {
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/* ECC Code Error Correction */
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read_ecc[0] = calc_ecc[0];
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read_ecc[1] = calc_ecc[1];
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read_ecc[2] = calc_ecc[2];
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return 2;
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} else {
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/* Uncorrectable Error */
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return -1;
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}
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}
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/* Check for a single bit error */
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if( ((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
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((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
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((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {
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uint32_t byteoffs, bitnum;
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byteoffs = (s1 << 0) & 0x80;
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byteoffs |= (s1 << 1) & 0x40;
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byteoffs |= (s1 << 2) & 0x20;
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byteoffs |= (s1 << 3) & 0x10;
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byteoffs |= (s0 >> 4) & 0x08;
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byteoffs |= (s0 >> 3) & 0x04;
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byteoffs |= (s0 >> 2) & 0x02;
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byteoffs |= (s0 >> 1) & 0x01;
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bitnum = (s2 >> 5) & 0x04;
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bitnum |= (s2 >> 4) & 0x02;
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bitnum |= (s2 >> 3) & 0x01;
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dat[byteoffs] ^= (1 << bitnum);
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return 1;
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}
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/* Should never happen */
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if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1)
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return 1;
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return -1;
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}
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EXPORT_SYMBOL(nand_calculate_ecc);
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EXPORT_SYMBOL(nand_correct_data);
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MODULE_LICENSE("GPL");
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