/* * 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 #include #include #include #include #else #include 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-byte block * @mtd: MTD block structure (unused) * @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; 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; 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; } /* * handle the fact that we use longword operations * we'll bring rp4..rp14 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; /* * 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 * 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 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 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; } EXPORT_SYMBOL(nand_calculate_ecc); /** * nand_correct_data - [NAND Interface] Detect and correct bit error(s) * @mtd: MTD block structure (unused) * @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 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; 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 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) && (((b2 ^ (b2 >> 1)) & 0x54) == 0x54)) { /* single bit error */ /* * 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; } /* 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 "); MODULE_DESCRIPTION("Generic NAND ECC support");