/* *  drivers/mtd/nand_ecc.c * *  Copyright (C) 2000 Steven J. Hill (sjhill@cotw.com) *                     Toshiba America Electronics Components, Inc. * * $Id: nand_ecc.c,v 1.1.1.1 2004/02/04 10:37:37 laputa Exp $ * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * This file contains an ECC algorithm from Toshiba that detects and * corrects 1 bit errors in a 256 byte block of data. */#include <types.h>/* * Pre-calculated 256-way 1 byte column parity */static const u_char 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};/* * 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;}/* * Calculate 3 byte ECC code for 256 byte block */void nand_calculate_ecc (const u_char *dat, u_char *ecc_code){	u_char idx, reg1, reg2, reg3;	int j;		/* 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++) {				/* Get CP0 - CP5 from table */		idx = nand_ecc_precalc_table[dat[j]];		reg1 ^= (idx & 0x3f);				/* All bit XOR = 1 ? */		if (idx & 0x40) {			reg3 ^= (u_char) j;			reg2 ^= ~((u_char) j);		}	}		/* Create non-inverted ECC code from line parity */	nand_trans_result(reg2, reg3, ecc_code);		/* Calculate final ECC code */	ecc_code[0] = ~ecc_code[0];	ecc_code[1] = ~ecc_code[1];	ecc_code[2] = ((~reg1) << 2) | 0x03;}/* * Detect and correct a 1 bit error for 256 byte block */int nand_correct_data (u_char *dat, u_char *read_ecc, u_char *calc_ecc){	u_char a, b, c, d1, d2, d3, add, bit, i;		/* 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 */		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;			}		}	}		/* Should never happen */	return -1;}