+/*\r
+ * Reed-Solomon ECC handling for the Marvell Kirkwood SOC\r
+ * Copyright (C) 2009 Marvell Semiconductor, Inc.\r
+ *\r
+ * Authors: Lennert Buytenhek <buytenh@wantstofly.org>\r
+ * Nicolas Pitre <nico@cam.org>\r
+ *\r
+ * This file is free software; you can redistribute it and/or modify it\r
+ * under the terms of the GNU General Public License as published by the\r
+ * Free Software Foundation; either version 2 or (at your option) any\r
+ * later version.\r
+ *\r
+ * This file is distributed in the hope that it will be useful, but WITHOUT\r
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or\r
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License\r
+ * for more details.\r
+ */\r
+\r
+#ifdef HAVE_CONFIG_H\r
+#include "config.h"\r
+#endif\r
+\r
+#include <sys/types.h>\r
+#include "nand.h"\r
+\r
+\r
+/*****************************************************************************\r
+ * Arithmetic in GF(2^10) ("F") modulo x^10 + x^3 + 1.\r
+ *\r
+ * For multiplication, a discrete log/exponent table is used, with\r
+ * primitive element x (F is a primitive field, so x is primitive).\r
+ */\r
+#define MODPOLY 0x409 /* x^10 + x^3 + 1 in binary */\r
+\r
+/*\r
+ * Maps an integer a [0..1022] to a polynomial b = gf_exp[a] in\r
+ * GF(2^10) mod x^10 + x^3 + 1 such that b = x ^ a. There's two\r
+ * identical copies of this array back-to-back so that we can save\r
+ * the mod 1023 operation when doing a GF multiplication.\r
+ */\r
+static uint16_t gf_exp[1023 + 1023];\r
+\r
+/*\r
+ * Maps a polynomial b in GF(2^10) mod x^10 + x^3 + 1 to an index\r
+ * a = gf_log[b] in [0..1022] such that b = x ^ a.\r
+ */\r
+static uint16_t gf_log[1024];\r
+\r
+static void gf_build_log_exp_table(void)\r
+{\r
+ int i;\r
+ int p_i;\r
+\r
+ /*\r
+ * p_i = x ^ i\r
+ *\r
+ * Initialise to 1 for i = 0.\r
+ */\r
+ p_i = 1;\r
+\r
+ for (i = 0; i < 1023; i++) {\r
+ gf_exp[i] = p_i;\r
+ gf_exp[i + 1023] = p_i;\r
+ gf_log[p_i] = i;\r
+\r
+ /*\r
+ * p_i = p_i * x\r
+ */\r
+ p_i <<= 1;\r
+ if (p_i & (1 << 10))\r
+ p_i ^= MODPOLY;\r
+ }\r
+}\r
+\r
+\r
+/*****************************************************************************\r
+ * Reed-Solomon code\r
+ *\r
+ * This implements a (1023,1015) Reed-Solomon ECC code over GF(2^10)\r
+ * mod x^10 + x^3 + 1, shortened to (520,512). The ECC data consists\r
+ * of 8 10-bit symbols, or 10 8-bit bytes.\r
+ *\r
+ * Given 512 bytes of data, computes 10 bytes of ECC.\r
+ *\r
+ * This is done by converting the 512 bytes to 512 10-bit symbols\r
+ * (elements of F), interpreting those symbols as a polynomial in F[X]\r
+ * by taking symbol 0 as the coefficient of X^8 and symbol 511 as the\r
+ * coefficient of X^519, and calculating the residue of that polynomial\r
+ * divided by the generator polynomial, which gives us the 8 ECC symbols\r
+ * as the remainder. Finally, we convert the 8 10-bit ECC symbols to 10\r
+ * 8-bit bytes.\r
+ *\r
+ * The generator polynomial is hardcoded, as that is faster, but it\r
+ * can be computed by taking the primitive element a = x (in F), and\r
+ * constructing a polynomial in F[X] with roots a, a^2, a^3, ..., a^8\r
+ * by multiplying the minimal polynomials for those roots (which are\r
+ * just 'x - a^i' for each i).\r
+ *\r
+ * Note: due to unfortunate circumstances, the bootrom in the Kirkwood SOC\r
+ * expects the ECC to be computed backward, i.e. from the last byte down\r
+ * to the first one.\r
+ */\r
+int nand_calculate_ecc_kw(struct nand_device_s *device, const u8 *data, u8 *ecc)\r
+{\r
+ unsigned int r7, r6, r5, r4, r3, r2, r1, r0;\r
+ int i;\r
+ static int tables_initialized = 0;\r
+\r
+ if (!tables_initialized) {\r
+ gf_build_log_exp_table();\r
+ tables_initialized = 1;\r
+ }\r
+\r
+ /*\r
+ * Load bytes 504..511 of the data into r.\r
+ */\r
+ r0 = data[504];\r
+ r1 = data[505];\r
+ r2 = data[506];\r
+ r3 = data[507];\r
+ r4 = data[508];\r
+ r5 = data[509];\r
+ r6 = data[510];\r
+ r7 = data[511];\r
+\r
+\r
+ /*\r
+ * Shift bytes 503..0 (in that order) into r0, followed\r
+ * by eight zero bytes, while reducing the polynomial by the\r
+ * generator polynomial in every step.\r
+ */\r
+ for (i = 503; i >= -8; i--) {\r
+ unsigned int d;\r
+\r
+ d = 0;\r
+ if (i >= 0)\r
+ d = data[i];\r
+\r
+ if (r7) {\r
+ u16 *t = gf_exp + gf_log[r7];\r
+\r
+ r7 = r6 ^ t[0x21c];\r
+ r6 = r5 ^ t[0x181];\r
+ r5 = r4 ^ t[0x18e];\r
+ r4 = r3 ^ t[0x25f];\r
+ r3 = r2 ^ t[0x197];\r
+ r2 = r1 ^ t[0x193];\r
+ r1 = r0 ^ t[0x237];\r
+ r0 = d ^ t[0x024];\r
+ } else {\r
+ r7 = r6;\r
+ r6 = r5;\r
+ r5 = r4;\r
+ r4 = r3;\r
+ r3 = r2;\r
+ r2 = r1;\r
+ r1 = r0;\r
+ r0 = d;\r
+ }\r
+ }\r
+\r
+ ecc[0] = r0;\r
+ ecc[1] = (r0 >> 8) | (r1 << 2);\r
+ ecc[2] = (r1 >> 6) | (r2 << 4);\r
+ ecc[3] = (r2 >> 4) | (r3 << 6);\r
+ ecc[4] = (r3 >> 2);\r
+ ecc[5] = r4;\r
+ ecc[6] = (r4 >> 8) | (r5 << 2);\r
+ ecc[7] = (r5 >> 6) | (r6 << 4);\r
+ ecc[8] = (r6 >> 4) | (r7 << 6);\r
+ ecc[9] = (r7 >> 2);\r
+\r
+ return 0;\r
+}\r