patch-2.4.6 linux/drivers/mtd/devices/docecc.c
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- Lines: 523
- Date:
Tue Jun 12 10:30:27 2001
- Orig file:
v2.4.5/linux/drivers/mtd/devices/docecc.c
- Orig date:
Wed Dec 31 16:00:00 1969
diff -u --recursive --new-file v2.4.5/linux/drivers/mtd/devices/docecc.c linux/drivers/mtd/devices/docecc.c
@@ -0,0 +1,522 @@
+/*
+ * ECC algorithm for M-systems disk on chip. We use the excellent Reed
+ * Solmon code of Phil Karn (karn@ka9q.ampr.org) available under the
+ * GNU GPL License. The rest is simply to convert the disk on chip
+ * syndrom into a standard syndom.
+ *
+ * Author: Fabrice Bellard (fabrice.bellard@netgem.com)
+ * Copyright (C) 2000 Netgem S.A.
+ *
+ * $Id: docecc.c,v 1.1 2000/11/03 12:43:43 dwmw2 Exp $
+ *
+ * This program 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 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <asm/errno.h>
+#include <asm/io.h>
+#include <asm/uaccess.h>
+#include <linux/miscdevice.h>
+#include <linux/pci.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/types.h>
+
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/doc2000.h>
+
+/* need to undef it (from asm/termbits.h) */
+#undef B0
+
+#define MM 10 /* Symbol size in bits */
+#define KK (1023-4) /* Number of data symbols per block */
+#define B0 510 /* First root of generator polynomial, alpha form */
+#define PRIM 1 /* power of alpha used to generate roots of generator poly */
+#define NN ((1 << MM) - 1)
+
+typedef unsigned short dtype;
+
+/* 1+x^3+x^10 */
+static const int Pp[MM+1] = { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1 };
+
+/* This defines the type used to store an element of the Galois Field
+ * used by the code. Make sure this is something larger than a char if
+ * if anything larger than GF(256) is used.
+ *
+ * Note: unsigned char will work up to GF(256) but int seems to run
+ * faster on the Pentium.
+ */
+typedef int gf;
+
+/* No legal value in index form represents zero, so
+ * we need a special value for this purpose
+ */
+#define A0 (NN)
+
+/* Compute x % NN, where NN is 2**MM - 1,
+ * without a slow divide
+ */
+static inline gf
+modnn(int x)
+{
+ while (x >= NN) {
+ x -= NN;
+ x = (x >> MM) + (x & NN);
+ }
+ return x;
+}
+
+#define min(a,b) ((a) < (b) ? (a) : (b))
+
+#define CLEAR(a,n) {\
+int ci;\
+for(ci=(n)-1;ci >=0;ci--)\
+(a)[ci] = 0;\
+}
+
+#define COPY(a,b,n) {\
+int ci;\
+for(ci=(n)-1;ci >=0;ci--)\
+(a)[ci] = (b)[ci];\
+}
+
+#define COPYDOWN(a,b,n) {\
+int ci;\
+for(ci=(n)-1;ci >=0;ci--)\
+(a)[ci] = (b)[ci];\
+}
+
+#define Ldec 1
+
+/* generate GF(2**m) from the irreducible polynomial p(X) in Pp[0]..Pp[m]
+ lookup tables: index->polynomial form alpha_to[] contains j=alpha**i;
+ polynomial form -> index form index_of[j=alpha**i] = i
+ alpha=2 is the primitive element of GF(2**m)
+ HARI's COMMENT: (4/13/94) alpha_to[] can be used as follows:
+ Let @ represent the primitive element commonly called "alpha" that
+ is the root of the primitive polynomial p(x). Then in GF(2^m), for any
+ 0 <= i <= 2^m-2,
+ @^i = a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1)
+ where the binary vector (a(0),a(1),a(2),...,a(m-1)) is the representation
+ of the integer "alpha_to[i]" with a(0) being the LSB and a(m-1) the MSB. Thus for
+ example the polynomial representation of @^5 would be given by the binary
+ representation of the integer "alpha_to[5]".
+ Similarily, index_of[] can be used as follows:
+ As above, let @ represent the primitive element of GF(2^m) that is
+ the root of the primitive polynomial p(x). In order to find the power
+ of @ (alpha) that has the polynomial representation
+ a(0) + a(1) @ + a(2) @^2 + ... + a(m-1) @^(m-1)
+ we consider the integer "i" whose binary representation with a(0) being LSB
+ and a(m-1) MSB is (a(0),a(1),...,a(m-1)) and locate the entry
+ "index_of[i]". Now, @^index_of[i] is that element whose polynomial
+ representation is (a(0),a(1),a(2),...,a(m-1)).
+ NOTE:
+ The element alpha_to[2^m-1] = 0 always signifying that the
+ representation of "@^infinity" = 0 is (0,0,0,...,0).
+ Similarily, the element index_of[0] = A0 always signifying
+ that the power of alpha which has the polynomial representation
+ (0,0,...,0) is "infinity".
+
+*/
+
+static void
+generate_gf(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1])
+{
+ register int i, mask;
+
+ mask = 1;
+ Alpha_to[MM] = 0;
+ for (i = 0; i < MM; i++) {
+ Alpha_to[i] = mask;
+ Index_of[Alpha_to[i]] = i;
+ /* If Pp[i] == 1 then, term @^i occurs in poly-repr of @^MM */
+ if (Pp[i] != 0)
+ Alpha_to[MM] ^= mask; /* Bit-wise EXOR operation */
+ mask <<= 1; /* single left-shift */
+ }
+ Index_of[Alpha_to[MM]] = MM;
+ /*
+ * Have obtained poly-repr of @^MM. Poly-repr of @^(i+1) is given by
+ * poly-repr of @^i shifted left one-bit and accounting for any @^MM
+ * term that may occur when poly-repr of @^i is shifted.
+ */
+ mask >>= 1;
+ for (i = MM + 1; i < NN; i++) {
+ if (Alpha_to[i - 1] >= mask)
+ Alpha_to[i] = Alpha_to[MM] ^ ((Alpha_to[i - 1] ^ mask) << 1);
+ else
+ Alpha_to[i] = Alpha_to[i - 1] << 1;
+ Index_of[Alpha_to[i]] = i;
+ }
+ Index_of[0] = A0;
+ Alpha_to[NN] = 0;
+}
+
+/*
+ * Performs ERRORS+ERASURES decoding of RS codes. bb[] is the content
+ * of the feedback shift register after having processed the data and
+ * the ECC.
+ *
+ * Return number of symbols corrected, or -1 if codeword is illegal
+ * or uncorrectable. If eras_pos is non-null, the detected error locations
+ * are written back. NOTE! This array must be at least NN-KK elements long.
+ * The corrected data are written in eras_val[]. They must be xor with the data
+ * to retrieve the correct data : data[erase_pos[i]] ^= erase_val[i] .
+ *
+ * First "no_eras" erasures are declared by the calling program. Then, the
+ * maximum # of errors correctable is t_after_eras = floor((NN-KK-no_eras)/2).
+ * If the number of channel errors is not greater than "t_after_eras" the
+ * transmitted codeword will be recovered. Details of algorithm can be found
+ * in R. Blahut's "Theory ... of Error-Correcting Codes".
+
+ * Warning: the eras_pos[] array must not contain duplicate entries; decoder failure
+ * will result. The decoder *could* check for this condition, but it would involve
+ * extra time on every decoding operation.
+ * */
+static int
+eras_dec_rs(dtype Alpha_to[NN + 1], dtype Index_of[NN + 1],
+ gf bb[NN - KK + 1], gf eras_val[NN-KK], int eras_pos[NN-KK],
+ int no_eras)
+{
+ int deg_lambda, el, deg_omega;
+ int i, j, r,k;
+ gf u,q,tmp,num1,num2,den,discr_r;
+ gf lambda[NN-KK + 1], s[NN-KK + 1]; /* Err+Eras Locator poly
+ * and syndrome poly */
+ gf b[NN-KK + 1], t[NN-KK + 1], omega[NN-KK + 1];
+ gf root[NN-KK], reg[NN-KK + 1], loc[NN-KK];
+ int syn_error, count;
+
+ syn_error = 0;
+ for(i=0;i<NN-KK;i++)
+ syn_error |= bb[i];
+
+ if (!syn_error) {
+ /* if remainder is zero, data[] is a codeword and there are no
+ * errors to correct. So return data[] unmodified
+ */
+ count = 0;
+ goto finish;
+ }
+
+ for(i=1;i<=NN-KK;i++){
+ s[i] = bb[0];
+ }
+ for(j=1;j<NN-KK;j++){
+ if(bb[j] == 0)
+ continue;
+ tmp = Index_of[bb[j]];
+
+ for(i=1;i<=NN-KK;i++)
+ s[i] ^= Alpha_to[modnn(tmp + (B0+i-1)*PRIM*j)];
+ }
+
+ /* undo the feedback register implicit multiplication and convert
+ syndromes to index form */
+
+ for(i=1;i<=NN-KK;i++) {
+ tmp = Index_of[s[i]];
+ if (tmp != A0)
+ tmp = modnn(tmp + 2 * KK * (B0+i-1)*PRIM);
+ s[i] = tmp;
+ }
+
+ CLEAR(&lambda[1],NN-KK);
+ lambda[0] = 1;
+
+ if (no_eras > 0) {
+ /* Init lambda to be the erasure locator polynomial */
+ lambda[1] = Alpha_to[modnn(PRIM * eras_pos[0])];
+ for (i = 1; i < no_eras; i++) {
+ u = modnn(PRIM*eras_pos[i]);
+ for (j = i+1; j > 0; j--) {
+ tmp = Index_of[lambda[j - 1]];
+ if(tmp != A0)
+ lambda[j] ^= Alpha_to[modnn(u + tmp)];
+ }
+ }
+#if DEBUG >= 1
+ /* Test code that verifies the erasure locator polynomial just constructed
+ Needed only for decoder debugging. */
+
+ /* find roots of the erasure location polynomial */
+ for(i=1;i<=no_eras;i++)
+ reg[i] = Index_of[lambda[i]];
+ count = 0;
+ for (i = 1,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) {
+ q = 1;
+ for (j = 1; j <= no_eras; j++)
+ if (reg[j] != A0) {
+ reg[j] = modnn(reg[j] + j);
+ q ^= Alpha_to[reg[j]];
+ }
+ if (q != 0)
+ continue;
+ /* store root and error location number indices */
+ root[count] = i;
+ loc[count] = k;
+ count++;
+ }
+ if (count != no_eras) {
+ printf("\n lambda(x) is WRONG\n");
+ count = -1;
+ goto finish;
+ }
+#if DEBUG >= 2
+ printf("\n Erasure positions as determined by roots of Eras Loc Poly:\n");
+ for (i = 0; i < count; i++)
+ printf("%d ", loc[i]);
+ printf("\n");
+#endif
+#endif
+ }
+ for(i=0;i<NN-KK+1;i++)
+ b[i] = Index_of[lambda[i]];
+
+ /*
+ * Begin Berlekamp-Massey algorithm to determine error+erasure
+ * locator polynomial
+ */
+ r = no_eras;
+ el = no_eras;
+ while (++r <= NN-KK) { /* r is the step number */
+ /* Compute discrepancy at the r-th step in poly-form */
+ discr_r = 0;
+ for (i = 0; i < r; i++){
+ if ((lambda[i] != 0) && (s[r - i] != A0)) {
+ discr_r ^= Alpha_to[modnn(Index_of[lambda[i]] + s[r - i])];
+ }
+ }
+ discr_r = Index_of[discr_r]; /* Index form */
+ if (discr_r == A0) {
+ /* 2 lines below: B(x) <-- x*B(x) */
+ COPYDOWN(&b[1],b,NN-KK);
+ b[0] = A0;
+ } else {
+ /* 7 lines below: T(x) <-- lambda(x) - discr_r*x*b(x) */
+ t[0] = lambda[0];
+ for (i = 0 ; i < NN-KK; i++) {
+ if(b[i] != A0)
+ t[i+1] = lambda[i+1] ^ Alpha_to[modnn(discr_r + b[i])];
+ else
+ t[i+1] = lambda[i+1];
+ }
+ if (2 * el <= r + no_eras - 1) {
+ el = r + no_eras - el;
+ /*
+ * 2 lines below: B(x) <-- inv(discr_r) *
+ * lambda(x)
+ */
+ for (i = 0; i <= NN-KK; i++)
+ b[i] = (lambda[i] == 0) ? A0 : modnn(Index_of[lambda[i]] - discr_r + NN);
+ } else {
+ /* 2 lines below: B(x) <-- x*B(x) */
+ COPYDOWN(&b[1],b,NN-KK);
+ b[0] = A0;
+ }
+ COPY(lambda,t,NN-KK+1);
+ }
+ }
+
+ /* Convert lambda to index form and compute deg(lambda(x)) */
+ deg_lambda = 0;
+ for(i=0;i<NN-KK+1;i++){
+ lambda[i] = Index_of[lambda[i]];
+ if(lambda[i] != A0)
+ deg_lambda = i;
+ }
+ /*
+ * Find roots of the error+erasure locator polynomial by Chien
+ * Search
+ */
+ COPY(®[1],&lambda[1],NN-KK);
+ count = 0; /* Number of roots of lambda(x) */
+ for (i = 1,k=NN-Ldec; i <= NN; i++,k = modnn(NN+k-Ldec)) {
+ q = 1;
+ for (j = deg_lambda; j > 0; j--){
+ if (reg[j] != A0) {
+ reg[j] = modnn(reg[j] + j);
+ q ^= Alpha_to[reg[j]];
+ }
+ }
+ if (q != 0)
+ continue;
+ /* store root (index-form) and error location number */
+ root[count] = i;
+ loc[count] = k;
+ /* If we've already found max possible roots,
+ * abort the search to save time
+ */
+ if(++count == deg_lambda)
+ break;
+ }
+ if (deg_lambda != count) {
+ /*
+ * deg(lambda) unequal to number of roots => uncorrectable
+ * error detected
+ */
+ count = -1;
+ goto finish;
+ }
+ /*
+ * Compute err+eras evaluator poly omega(x) = s(x)*lambda(x) (modulo
+ * x**(NN-KK)). in index form. Also find deg(omega).
+ */
+ deg_omega = 0;
+ for (i = 0; i < NN-KK;i++){
+ tmp = 0;
+ j = (deg_lambda < i) ? deg_lambda : i;
+ for(;j >= 0; j--){
+ if ((s[i + 1 - j] != A0) && (lambda[j] != A0))
+ tmp ^= Alpha_to[modnn(s[i + 1 - j] + lambda[j])];
+ }
+ if(tmp != 0)
+ deg_omega = i;
+ omega[i] = Index_of[tmp];
+ }
+ omega[NN-KK] = A0;
+
+ /*
+ * Compute error values in poly-form. num1 = omega(inv(X(l))), num2 =
+ * inv(X(l))**(B0-1) and den = lambda_pr(inv(X(l))) all in poly-form
+ */
+ for (j = count-1; j >=0; j--) {
+ num1 = 0;
+ for (i = deg_omega; i >= 0; i--) {
+ if (omega[i] != A0)
+ num1 ^= Alpha_to[modnn(omega[i] + i * root[j])];
+ }
+ num2 = Alpha_to[modnn(root[j] * (B0 - 1) + NN)];
+ den = 0;
+
+ /* lambda[i+1] for i even is the formal derivative lambda_pr of lambda[i] */
+ for (i = min(deg_lambda,NN-KK-1) & ~1; i >= 0; i -=2) {
+ if(lambda[i+1] != A0)
+ den ^= Alpha_to[modnn(lambda[i+1] + i * root[j])];
+ }
+ if (den == 0) {
+#if DEBUG >= 1
+ printf("\n ERROR: denominator = 0\n");
+#endif
+ /* Convert to dual- basis */
+ count = -1;
+ goto finish;
+ }
+ /* Apply error to data */
+ if (num1 != 0) {
+ eras_val[j] = Alpha_to[modnn(Index_of[num1] + Index_of[num2] + NN - Index_of[den])];
+ } else {
+ eras_val[j] = 0;
+ }
+ }
+ finish:
+ for(i=0;i<count;i++)
+ eras_pos[i] = loc[i];
+ return count;
+}
+
+/***************************************************************************/
+/* The DOC specific code begins here */
+
+#define SECTOR_SIZE 512
+/* The sector bytes are packed into NB_DATA MM bits words */
+#define NB_DATA (((SECTOR_SIZE + 1) * 8 + 6) / MM)
+
+/*
+ * Correct the errors in 'sector[]' by using 'ecc1[]' which is the
+ * content of the feedback shift register applyied to the sector and
+ * the ECC. Return the number of errors corrected (and correct them in
+ * sector), or -1 if error
+ */
+int doc_decode_ecc(unsigned char sector[SECTOR_SIZE], unsigned char ecc1[6])
+{
+ int parity, i, nb_errors;
+ gf bb[NN - KK + 1];
+ gf error_val[NN-KK];
+ int error_pos[NN-KK], pos, bitpos, index, val;
+ dtype *Alpha_to, *Index_of;
+
+ /* init log and exp tables here to save memory. However, it is slower */
+ Alpha_to = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL);
+ if (!Alpha_to)
+ return -1;
+
+ Index_of = kmalloc((NN + 1) * sizeof(dtype), GFP_KERNEL);
+ if (!Index_of) {
+ kfree(Alpha_to);
+ return -1;
+ }
+
+ generate_gf(Alpha_to, Index_of);
+
+ parity = ecc1[1];
+
+ bb[0] = (ecc1[4] & 0xff) | ((ecc1[5] & 0x03) << 8);
+ bb[1] = ((ecc1[5] & 0xfc) >> 2) | ((ecc1[2] & 0x0f) << 6);
+ bb[2] = ((ecc1[2] & 0xf0) >> 4) | ((ecc1[3] & 0x3f) << 4);
+ bb[3] = ((ecc1[3] & 0xc0) >> 6) | ((ecc1[0] & 0xff) << 2);
+
+ nb_errors = eras_dec_rs(Alpha_to, Index_of, bb,
+ error_val, error_pos, 0);
+ if (nb_errors <= 0)
+ goto the_end;
+
+ /* correct the errors */
+ for(i=0;i<nb_errors;i++) {
+ pos = error_pos[i];
+ if (pos >= NB_DATA && pos < KK) {
+ nb_errors = -1;
+ goto the_end;
+ }
+ if (pos < NB_DATA) {
+ /* extract bit position (MSB first) */
+ pos = 10 * (NB_DATA - 1 - pos) - 6;
+ /* now correct the following 10 bits. At most two bytes
+ can be modified since pos is even */
+ index = (pos >> 3) ^ 1;
+ bitpos = pos & 7;
+ if ((index >= 0 && index < SECTOR_SIZE) ||
+ index == (SECTOR_SIZE + 1)) {
+ val = error_val[i] >> (2 + bitpos);
+ parity ^= val;
+ if (index < SECTOR_SIZE)
+ sector[index] ^= val;
+ }
+ index = ((pos >> 3) + 1) ^ 1;
+ bitpos = (bitpos + 10) & 7;
+ if (bitpos == 0)
+ bitpos = 8;
+ if ((index >= 0 && index < SECTOR_SIZE) ||
+ index == (SECTOR_SIZE + 1)) {
+ val = error_val[i] << (8 - bitpos);
+ parity ^= val;
+ if (index < SECTOR_SIZE)
+ sector[index] ^= val;
+ }
+ }
+ }
+
+ /* use parity to test extra errors */
+ if ((parity & 0xff) != 0)
+ nb_errors = -1;
+
+ the_end:
+ kfree(Alpha_to);
+ kfree(Index_of);
+ return nb_errors;
+}
+
FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)