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- /*
- * Reed-Solomon ECC handling for the Marvell Kirkwood SOC
- * Copyright (C) 2009 Marvell Semiconductor, Inc.
- *
- * Authors: Lennert Buytenhek <buytenh@wantstofly.org>
- * Nicolas Pitre <nico@fluxnic.net>
- *
- * 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.
- */
-
- #ifdef HAVE_CONFIG_H
- #include "config.h"
- #endif
-
- #include "core.h"
-
- /*****************************************************************************
- * Arithmetic in GF(2^10) ("F") modulo x^10 + x^3 + 1.
- *
- * For multiplication, a discrete log/exponent table is used, with
- * primitive element x (F is a primitive field, so x is primitive).
- */
- #define MODPOLY 0x409 /* x^10 + x^3 + 1 in binary */
-
- /*
- * Maps an integer a [0..1022] to a polynomial b = gf_exp[a] in
- * GF(2^10) mod x^10 + x^3 + 1 such that b = x ^ a. There's two
- * identical copies of this array back-to-back so that we can save
- * the mod 1023 operation when doing a GF multiplication.
- */
- static uint16_t gf_exp[1023 + 1023];
-
- /*
- * Maps a polynomial b in GF(2^10) mod x^10 + x^3 + 1 to an index
- * a = gf_log[b] in [0..1022] such that b = x ^ a.
- */
- static uint16_t gf_log[1024];
-
- static void gf_build_log_exp_table(void)
- {
- int i;
- int p_i;
-
- /*
- * p_i = x ^ i
- *
- * Initialise to 1 for i = 0.
- */
- p_i = 1;
-
- for (i = 0; i < 1023; i++) {
- gf_exp[i] = p_i;
- gf_exp[i + 1023] = p_i;
- gf_log[p_i] = i;
-
- /*
- * p_i = p_i * x
- */
- p_i <<= 1;
- if (p_i & (1 << 10))
- p_i ^= MODPOLY;
- }
- }
-
-
- /*****************************************************************************
- * Reed-Solomon code
- *
- * This implements a (1023,1015) Reed-Solomon ECC code over GF(2^10)
- * mod x^10 + x^3 + 1, shortened to (520,512). The ECC data consists
- * of 8 10-bit symbols, or 10 8-bit bytes.
- *
- * Given 512 bytes of data, computes 10 bytes of ECC.
- *
- * This is done by converting the 512 bytes to 512 10-bit symbols
- * (elements of F), interpreting those symbols as a polynomial in F[X]
- * by taking symbol 0 as the coefficient of X^8 and symbol 511 as the
- * coefficient of X^519, and calculating the residue of that polynomial
- * divided by the generator polynomial, which gives us the 8 ECC symbols
- * as the remainder. Finally, we convert the 8 10-bit ECC symbols to 10
- * 8-bit bytes.
- *
- * The generator polynomial is hardcoded, as that is faster, but it
- * can be computed by taking the primitive element a = x (in F), and
- * constructing a polynomial in F[X] with roots a, a^2, a^3, ..., a^8
- * by multiplying the minimal polynomials for those roots (which are
- * just 'x - a^i' for each i).
- *
- * Note: due to unfortunate circumstances, the bootrom in the Kirkwood SOC
- * expects the ECC to be computed backward, i.e. from the last byte down
- * to the first one.
- */
- int nand_calculate_ecc_kw(struct nand_device *nand, const uint8_t *data, uint8_t *ecc)
- {
- unsigned int r7, r6, r5, r4, r3, r2, r1, r0;
- int i;
- static int tables_initialized = 0;
-
- if (!tables_initialized) {
- gf_build_log_exp_table();
- tables_initialized = 1;
- }
-
- /*
- * Load bytes 504..511 of the data into r.
- */
- r0 = data[504];
- r1 = data[505];
- r2 = data[506];
- r3 = data[507];
- r4 = data[508];
- r5 = data[509];
- r6 = data[510];
- r7 = data[511];
-
-
- /*
- * Shift bytes 503..0 (in that order) into r0, followed
- * by eight zero bytes, while reducing the polynomial by the
- * generator polynomial in every step.
- */
- for (i = 503; i >= -8; i--) {
- unsigned int d;
-
- d = 0;
- if (i >= 0)
- d = data[i];
-
- if (r7) {
- uint16_t *t = gf_exp + gf_log[r7];
-
- r7 = r6 ^ t[0x21c];
- r6 = r5 ^ t[0x181];
- r5 = r4 ^ t[0x18e];
- r4 = r3 ^ t[0x25f];
- r3 = r2 ^ t[0x197];
- r2 = r1 ^ t[0x193];
- r1 = r0 ^ t[0x237];
- r0 = d ^ t[0x024];
- } else {
- r7 = r6;
- r6 = r5;
- r5 = r4;
- r4 = r3;
- r3 = r2;
- r2 = r1;
- r1 = r0;
- r0 = d;
- }
- }
-
- ecc[0] = r0;
- ecc[1] = (r0 >> 8) | (r1 << 2);
- ecc[2] = (r1 >> 6) | (r2 << 4);
- ecc[3] = (r2 >> 4) | (r3 << 6);
- ecc[4] = (r3 >> 2);
- ecc[5] = r4;
- ecc[6] = (r4 >> 8) | (r5 << 2);
- ecc[7] = (r5 >> 6) | (r6 << 4);
- ecc[8] = (r6 >> 4) | (r7 << 6);
- ecc[9] = (r7 >> 2);
-
- return 0;
- }
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