drivers/mtd/nand/nand_ecc.c - kernel/msm-4.9 - Gitiles

 /*
  * 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, bit_addr;
 	unsigned int byte_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");
	/*
	* 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, bit_addr;
	unsigned int byte_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");