patch-2.4.6 linux/drivers/mtd/docecc.c
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- Lines: 523
- Date:
Wed Dec 31 16:00:00 1969
- Orig file:
v2.4.5/linux/drivers/mtd/docecc.c
- Orig date:
Fri Feb 9 11:30:23 2001
diff -u --recursive --new-file v2.4.5/linux/drivers/mtd/docecc.c linux/drivers/mtd/docecc.c
@@ -1,522 +0,0 @@
-/*
- * 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)