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Christian Hitz4c6de852011-10-12 09:31:59 +02001/*
2 * Generic binary BCH encoding/decoding library
3 *
Tom Rini5b8031c2016-01-14 22:05:13 -05004 * SPDX-License-Identifier: GPL-2.0
Christian Hitz4c6de852011-10-12 09:31:59 +02005 *
6 * Copyright © 2011 Parrot S.A.
7 *
8 * Author: Ivan Djelic <ivan.djelic@parrot.com>
9 *
10 * Description:
11 *
12 * This library provides runtime configurable encoding/decoding of binary
13 * Bose-Chaudhuri-Hocquenghem (BCH) codes.
14 *
15 * Call init_bch to get a pointer to a newly allocated bch_control structure for
16 * the given m (Galois field order), t (error correction capability) and
17 * (optional) primitive polynomial parameters.
18 *
19 * Call encode_bch to compute and store ecc parity bytes to a given buffer.
20 * Call decode_bch to detect and locate errors in received data.
21 *
22 * On systems supporting hw BCH features, intermediate results may be provided
23 * to decode_bch in order to skip certain steps. See decode_bch() documentation
24 * for details.
25 *
26 * Option CONFIG_BCH_CONST_PARAMS can be used to force fixed values of
27 * parameters m and t; thus allowing extra compiler optimizations and providing
28 * better (up to 2x) encoding performance. Using this option makes sense when
29 * (m,t) are fixed and known in advance, e.g. when using BCH error correction
30 * on a particular NAND flash device.
31 *
32 * Algorithmic details:
33 *
34 * Encoding is performed by processing 32 input bits in parallel, using 4
35 * remainder lookup tables.
36 *
37 * The final stage of decoding involves the following internal steps:
38 * a. Syndrome computation
39 * b. Error locator polynomial computation using Berlekamp-Massey algorithm
40 * c. Error locator root finding (by far the most expensive step)
41 *
42 * In this implementation, step c is not performed using the usual Chien search.
43 * Instead, an alternative approach described in [1] is used. It consists in
44 * factoring the error locator polynomial using the Berlekamp Trace algorithm
45 * (BTA) down to a certain degree (4), after which ad hoc low-degree polynomial
46 * solving techniques [2] are used. The resulting algorithm, called BTZ, yields
47 * much better performance than Chien search for usual (m,t) values (typically
48 * m >= 13, t < 32, see [1]).
49 *
50 * [1] B. Biswas, V. Herbert. Efficient root finding of polynomials over fields
51 * of characteristic 2, in: Western European Workshop on Research in Cryptology
52 * - WEWoRC 2009, Graz, Austria, LNCS, Springer, July 2009, to appear.
53 * [2] [Zin96] V.A. Zinoviev. On the solution of equations of degree 10 over
54 * finite fields GF(2^q). In Rapport de recherche INRIA no 2829, 1996.
55 */
56
Maxime Ripard71d2c072017-02-27 18:22:01 +010057#ifndef USE_HOSTCC
Christian Hitz4c6de852011-10-12 09:31:59 +020058#include <common.h>
59#include <ubi_uboot.h>
60
61#include <linux/bitops.h>
Maxime Ripard71d2c072017-02-27 18:22:01 +010062#else
63#include <errno.h>
Emmanuel Vadot4ecc9882017-06-20 09:02:29 +020064#if defined(__FreeBSD__)
65#include <sys/endian.h>
66#else
Maxime Ripard71d2c072017-02-27 18:22:01 +010067#include <endian.h>
Emmanuel Vadot4ecc9882017-06-20 09:02:29 +020068#endif
Maxime Ripard71d2c072017-02-27 18:22:01 +010069#include <stdint.h>
70#include <stdlib.h>
71#include <string.h>
72
73#undef cpu_to_be32
74#define cpu_to_be32 htobe32
75#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
76#define kmalloc(size, flags) malloc(size)
77#define kzalloc(size, flags) calloc(1, size)
78#define kfree free
79#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
80#endif
81
Christian Hitz4c6de852011-10-12 09:31:59 +020082#include <asm/byteorder.h>
83#include <linux/bch.h>
84
85#if defined(CONFIG_BCH_CONST_PARAMS)
86#define GF_M(_p) (CONFIG_BCH_CONST_M)
87#define GF_T(_p) (CONFIG_BCH_CONST_T)
88#define GF_N(_p) ((1 << (CONFIG_BCH_CONST_M))-1)
89#else
90#define GF_M(_p) ((_p)->m)
91#define GF_T(_p) ((_p)->t)
92#define GF_N(_p) ((_p)->n)
93#endif
94
95#define BCH_ECC_WORDS(_p) DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 32)
96#define BCH_ECC_BYTES(_p) DIV_ROUND_UP(GF_M(_p)*GF_T(_p), 8)
97
98#ifndef dbg
99#define dbg(_fmt, args...) do {} while (0)
100#endif
101
102/*
103 * represent a polynomial over GF(2^m)
104 */
105struct gf_poly {
106 unsigned int deg; /* polynomial degree */
107 unsigned int c[0]; /* polynomial terms */
108};
109
110/* given its degree, compute a polynomial size in bytes */
111#define GF_POLY_SZ(_d) (sizeof(struct gf_poly)+((_d)+1)*sizeof(unsigned int))
112
113/* polynomial of degree 1 */
114struct gf_poly_deg1 {
115 struct gf_poly poly;
116 unsigned int c[2];
117};
118
Maxime Ripard71d2c072017-02-27 18:22:01 +0100119#ifdef USE_HOSTCC
Emmanuel Vadot4ecc9882017-06-20 09:02:29 +0200120#ifndef __BSD_VISIBLE
Maxime Ripard71d2c072017-02-27 18:22:01 +0100121static int fls(int x)
122{
123 int r = 32;
124
125 if (!x)
126 return 0;
127 if (!(x & 0xffff0000u)) {
128 x <<= 16;
129 r -= 16;
130 }
131 if (!(x & 0xff000000u)) {
132 x <<= 8;
133 r -= 8;
134 }
135 if (!(x & 0xf0000000u)) {
136 x <<= 4;
137 r -= 4;
138 }
139 if (!(x & 0xc0000000u)) {
140 x <<= 2;
141 r -= 2;
142 }
143 if (!(x & 0x80000000u)) {
144 x <<= 1;
145 r -= 1;
146 }
147 return r;
148}
149#endif
Emmanuel Vadot4ecc9882017-06-20 09:02:29 +0200150#endif
Maxime Ripard71d2c072017-02-27 18:22:01 +0100151
Christian Hitz4c6de852011-10-12 09:31:59 +0200152/*
153 * same as encode_bch(), but process input data one byte at a time
154 */
155static void encode_bch_unaligned(struct bch_control *bch,
156 const unsigned char *data, unsigned int len,
157 uint32_t *ecc)
158{
159 int i;
160 const uint32_t *p;
161 const int l = BCH_ECC_WORDS(bch)-1;
162
163 while (len--) {
164 p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(*data++)) & 0xff);
165
166 for (i = 0; i < l; i++)
167 ecc[i] = ((ecc[i] << 8)|(ecc[i+1] >> 24))^(*p++);
168
169 ecc[l] = (ecc[l] << 8)^(*p);
170 }
171}
172
173/*
174 * convert ecc bytes to aligned, zero-padded 32-bit ecc words
175 */
176static void load_ecc8(struct bch_control *bch, uint32_t *dst,
177 const uint8_t *src)
178{
179 uint8_t pad[4] = {0, 0, 0, 0};
180 unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
181
182 for (i = 0; i < nwords; i++, src += 4)
183 dst[i] = (src[0] << 24)|(src[1] << 16)|(src[2] << 8)|src[3];
184
185 memcpy(pad, src, BCH_ECC_BYTES(bch)-4*nwords);
186 dst[nwords] = (pad[0] << 24)|(pad[1] << 16)|(pad[2] << 8)|pad[3];
187}
188
189/*
190 * convert 32-bit ecc words to ecc bytes
191 */
192static void store_ecc8(struct bch_control *bch, uint8_t *dst,
193 const uint32_t *src)
194{
195 uint8_t pad[4];
196 unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
197
198 for (i = 0; i < nwords; i++) {
199 *dst++ = (src[i] >> 24);
200 *dst++ = (src[i] >> 16) & 0xff;
201 *dst++ = (src[i] >> 8) & 0xff;
202 *dst++ = (src[i] >> 0) & 0xff;
203 }
204 pad[0] = (src[nwords] >> 24);
205 pad[1] = (src[nwords] >> 16) & 0xff;
206 pad[2] = (src[nwords] >> 8) & 0xff;
207 pad[3] = (src[nwords] >> 0) & 0xff;
208 memcpy(dst, pad, BCH_ECC_BYTES(bch)-4*nwords);
209}
210
211/**
212 * encode_bch - calculate BCH ecc parity of data
213 * @bch: BCH control structure
214 * @data: data to encode
215 * @len: data length in bytes
216 * @ecc: ecc parity data, must be initialized by caller
217 *
218 * The @ecc parity array is used both as input and output parameter, in order to
219 * allow incremental computations. It should be of the size indicated by member
220 * @ecc_bytes of @bch, and should be initialized to 0 before the first call.
221 *
222 * The exact number of computed ecc parity bits is given by member @ecc_bits of
223 * @bch; it may be less than m*t for large values of t.
224 */
225void encode_bch(struct bch_control *bch, const uint8_t *data,
226 unsigned int len, uint8_t *ecc)
227{
228 const unsigned int l = BCH_ECC_WORDS(bch)-1;
229 unsigned int i, mlen;
230 unsigned long m;
231 uint32_t w, r[l+1];
232 const uint32_t * const tab0 = bch->mod8_tab;
233 const uint32_t * const tab1 = tab0 + 256*(l+1);
234 const uint32_t * const tab2 = tab1 + 256*(l+1);
235 const uint32_t * const tab3 = tab2 + 256*(l+1);
236 const uint32_t *pdata, *p0, *p1, *p2, *p3;
237
238 if (ecc) {
239 /* load ecc parity bytes into internal 32-bit buffer */
240 load_ecc8(bch, bch->ecc_buf, ecc);
241 } else {
242 memset(bch->ecc_buf, 0, sizeof(r));
243 }
244
245 /* process first unaligned data bytes */
246 m = ((unsigned long)data) & 3;
247 if (m) {
248 mlen = (len < (4-m)) ? len : 4-m;
249 encode_bch_unaligned(bch, data, mlen, bch->ecc_buf);
250 data += mlen;
251 len -= mlen;
252 }
253
254 /* process 32-bit aligned data words */
255 pdata = (uint32_t *)data;
256 mlen = len/4;
257 data += 4*mlen;
258 len -= 4*mlen;
259 memcpy(r, bch->ecc_buf, sizeof(r));
260
261 /*
262 * split each 32-bit word into 4 polynomials of weight 8 as follows:
263 *
264 * 31 ...24 23 ...16 15 ... 8 7 ... 0
265 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt
266 * tttttttt mod g = r0 (precomputed)
267 * zzzzzzzz 00000000 mod g = r1 (precomputed)
268 * yyyyyyyy 00000000 00000000 mod g = r2 (precomputed)
269 * xxxxxxxx 00000000 00000000 00000000 mod g = r3 (precomputed)
270 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt mod g = r0^r1^r2^r3
271 */
272 while (mlen--) {
273 /* input data is read in big-endian format */
274 w = r[0]^cpu_to_be32(*pdata++);
275 p0 = tab0 + (l+1)*((w >> 0) & 0xff);
276 p1 = tab1 + (l+1)*((w >> 8) & 0xff);
277 p2 = tab2 + (l+1)*((w >> 16) & 0xff);
278 p3 = tab3 + (l+1)*((w >> 24) & 0xff);
279
280 for (i = 0; i < l; i++)
281 r[i] = r[i+1]^p0[i]^p1[i]^p2[i]^p3[i];
282
283 r[l] = p0[l]^p1[l]^p2[l]^p3[l];
284 }
285 memcpy(bch->ecc_buf, r, sizeof(r));
286
287 /* process last unaligned bytes */
288 if (len)
289 encode_bch_unaligned(bch, data, len, bch->ecc_buf);
290
291 /* store ecc parity bytes into original parity buffer */
292 if (ecc)
293 store_ecc8(bch, ecc, bch->ecc_buf);
294}
295
296static inline int modulo(struct bch_control *bch, unsigned int v)
297{
298 const unsigned int n = GF_N(bch);
299 while (v >= n) {
300 v -= n;
301 v = (v & n) + (v >> GF_M(bch));
302 }
303 return v;
304}
305
306/*
307 * shorter and faster modulo function, only works when v < 2N.
308 */
309static inline int mod_s(struct bch_control *bch, unsigned int v)
310{
311 const unsigned int n = GF_N(bch);
312 return (v < n) ? v : v-n;
313}
314
315static inline int deg(unsigned int poly)
316{
317 /* polynomial degree is the most-significant bit index */
318 return fls(poly)-1;
319}
320
321static inline int parity(unsigned int x)
322{
323 /*
324 * public domain code snippet, lifted from
325 * http://www-graphics.stanford.edu/~seander/bithacks.html
326 */
327 x ^= x >> 1;
328 x ^= x >> 2;
329 x = (x & 0x11111111U) * 0x11111111U;
330 return (x >> 28) & 1;
331}
332
333/* Galois field basic operations: multiply, divide, inverse, etc. */
334
335static inline unsigned int gf_mul(struct bch_control *bch, unsigned int a,
336 unsigned int b)
337{
338 return (a && b) ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
339 bch->a_log_tab[b])] : 0;
340}
341
342static inline unsigned int gf_sqr(struct bch_control *bch, unsigned int a)
343{
344 return a ? bch->a_pow_tab[mod_s(bch, 2*bch->a_log_tab[a])] : 0;
345}
346
347static inline unsigned int gf_div(struct bch_control *bch, unsigned int a,
348 unsigned int b)
349{
350 return a ? bch->a_pow_tab[mod_s(bch, bch->a_log_tab[a]+
351 GF_N(bch)-bch->a_log_tab[b])] : 0;
352}
353
354static inline unsigned int gf_inv(struct bch_control *bch, unsigned int a)
355{
356 return bch->a_pow_tab[GF_N(bch)-bch->a_log_tab[a]];
357}
358
359static inline unsigned int a_pow(struct bch_control *bch, int i)
360{
361 return bch->a_pow_tab[modulo(bch, i)];
362}
363
364static inline int a_log(struct bch_control *bch, unsigned int x)
365{
366 return bch->a_log_tab[x];
367}
368
369static inline int a_ilog(struct bch_control *bch, unsigned int x)
370{
371 return mod_s(bch, GF_N(bch)-bch->a_log_tab[x]);
372}
373
374/*
375 * compute 2t syndromes of ecc polynomial, i.e. ecc(a^j) for j=1..2t
376 */
377static void compute_syndromes(struct bch_control *bch, uint32_t *ecc,
378 unsigned int *syn)
379{
380 int i, j, s;
381 unsigned int m;
382 uint32_t poly;
383 const int t = GF_T(bch);
384
385 s = bch->ecc_bits;
386
387 /* make sure extra bits in last ecc word are cleared */
388 m = ((unsigned int)s) & 31;
389 if (m)
390 ecc[s/32] &= ~((1u << (32-m))-1);
391 memset(syn, 0, 2*t*sizeof(*syn));
392
393 /* compute v(a^j) for j=1 .. 2t-1 */
394 do {
395 poly = *ecc++;
396 s -= 32;
397 while (poly) {
398 i = deg(poly);
399 for (j = 0; j < 2*t; j += 2)
400 syn[j] ^= a_pow(bch, (j+1)*(i+s));
401
402 poly ^= (1 << i);
403 }
404 } while (s > 0);
405
406 /* v(a^(2j)) = v(a^j)^2 */
407 for (j = 0; j < t; j++)
408 syn[2*j+1] = gf_sqr(bch, syn[j]);
409}
410
411static void gf_poly_copy(struct gf_poly *dst, struct gf_poly *src)
412{
413 memcpy(dst, src, GF_POLY_SZ(src->deg));
414}
415
416static int compute_error_locator_polynomial(struct bch_control *bch,
417 const unsigned int *syn)
418{
419 const unsigned int t = GF_T(bch);
420 const unsigned int n = GF_N(bch);
421 unsigned int i, j, tmp, l, pd = 1, d = syn[0];
422 struct gf_poly *elp = bch->elp;
423 struct gf_poly *pelp = bch->poly_2t[0];
424 struct gf_poly *elp_copy = bch->poly_2t[1];
425 int k, pp = -1;
426
427 memset(pelp, 0, GF_POLY_SZ(2*t));
428 memset(elp, 0, GF_POLY_SZ(2*t));
429
430 pelp->deg = 0;
431 pelp->c[0] = 1;
432 elp->deg = 0;
433 elp->c[0] = 1;
434
435 /* use simplified binary Berlekamp-Massey algorithm */
436 for (i = 0; (i < t) && (elp->deg <= t); i++) {
437 if (d) {
438 k = 2*i-pp;
439 gf_poly_copy(elp_copy, elp);
440 /* e[i+1](X) = e[i](X)+di*dp^-1*X^2(i-p)*e[p](X) */
441 tmp = a_log(bch, d)+n-a_log(bch, pd);
442 for (j = 0; j <= pelp->deg; j++) {
443 if (pelp->c[j]) {
444 l = a_log(bch, pelp->c[j]);
445 elp->c[j+k] ^= a_pow(bch, tmp+l);
446 }
447 }
448 /* compute l[i+1] = max(l[i]->c[l[p]+2*(i-p]) */
449 tmp = pelp->deg+k;
450 if (tmp > elp->deg) {
451 elp->deg = tmp;
452 gf_poly_copy(pelp, elp_copy);
453 pd = d;
454 pp = 2*i;
455 }
456 }
457 /* di+1 = S(2i+3)+elp[i+1].1*S(2i+2)+...+elp[i+1].lS(2i+3-l) */
458 if (i < t-1) {
459 d = syn[2*i+2];
460 for (j = 1; j <= elp->deg; j++)
461 d ^= gf_mul(bch, elp->c[j], syn[2*i+2-j]);
462 }
463 }
464 dbg("elp=%s\n", gf_poly_str(elp));
465 return (elp->deg > t) ? -1 : (int)elp->deg;
466}
467
468/*
469 * solve a m x m linear system in GF(2) with an expected number of solutions,
470 * and return the number of found solutions
471 */
472static int solve_linear_system(struct bch_control *bch, unsigned int *rows,
473 unsigned int *sol, int nsol)
474{
475 const int m = GF_M(bch);
476 unsigned int tmp, mask;
477 int rem, c, r, p, k, param[m];
478
479 k = 0;
480 mask = 1 << m;
481
482 /* Gaussian elimination */
483 for (c = 0; c < m; c++) {
484 rem = 0;
485 p = c-k;
486 /* find suitable row for elimination */
487 for (r = p; r < m; r++) {
488 if (rows[r] & mask) {
489 if (r != p) {
490 tmp = rows[r];
491 rows[r] = rows[p];
492 rows[p] = tmp;
493 }
494 rem = r+1;
495 break;
496 }
497 }
498 if (rem) {
499 /* perform elimination on remaining rows */
500 tmp = rows[p];
501 for (r = rem; r < m; r++) {
502 if (rows[r] & mask)
503 rows[r] ^= tmp;
504 }
505 } else {
506 /* elimination not needed, store defective row index */
507 param[k++] = c;
508 }
509 mask >>= 1;
510 }
511 /* rewrite system, inserting fake parameter rows */
512 if (k > 0) {
513 p = k;
514 for (r = m-1; r >= 0; r--) {
515 if ((r > m-1-k) && rows[r])
516 /* system has no solution */
517 return 0;
518
519 rows[r] = (p && (r == param[p-1])) ?
520 p--, 1u << (m-r) : rows[r-p];
521 }
522 }
523
524 if (nsol != (1 << k))
525 /* unexpected number of solutions */
526 return 0;
527
528 for (p = 0; p < nsol; p++) {
529 /* set parameters for p-th solution */
530 for (c = 0; c < k; c++)
531 rows[param[c]] = (rows[param[c]] & ~1)|((p >> c) & 1);
532
533 /* compute unique solution */
534 tmp = 0;
535 for (r = m-1; r >= 0; r--) {
536 mask = rows[r] & (tmp|1);
537 tmp |= parity(mask) << (m-r);
538 }
539 sol[p] = tmp >> 1;
540 }
541 return nsol;
542}
543
544/*
545 * this function builds and solves a linear system for finding roots of a degree
546 * 4 affine monic polynomial X^4+aX^2+bX+c over GF(2^m).
547 */
548static int find_affine4_roots(struct bch_control *bch, unsigned int a,
549 unsigned int b, unsigned int c,
550 unsigned int *roots)
551{
552 int i, j, k;
553 const int m = GF_M(bch);
554 unsigned int mask = 0xff, t, rows[16] = {0,};
555
556 j = a_log(bch, b);
557 k = a_log(bch, a);
558 rows[0] = c;
559
560 /* buid linear system to solve X^4+aX^2+bX+c = 0 */
561 for (i = 0; i < m; i++) {
562 rows[i+1] = bch->a_pow_tab[4*i]^
563 (a ? bch->a_pow_tab[mod_s(bch, k)] : 0)^
564 (b ? bch->a_pow_tab[mod_s(bch, j)] : 0);
565 j++;
566 k += 2;
567 }
568 /*
569 * transpose 16x16 matrix before passing it to linear solver
570 * warning: this code assumes m < 16
571 */
572 for (j = 8; j != 0; j >>= 1, mask ^= (mask << j)) {
573 for (k = 0; k < 16; k = (k+j+1) & ~j) {
574 t = ((rows[k] >> j)^rows[k+j]) & mask;
575 rows[k] ^= (t << j);
576 rows[k+j] ^= t;
577 }
578 }
579 return solve_linear_system(bch, rows, roots, 4);
580}
581
582/*
583 * compute root r of a degree 1 polynomial over GF(2^m) (returned as log(1/r))
584 */
585static int find_poly_deg1_roots(struct bch_control *bch, struct gf_poly *poly,
586 unsigned int *roots)
587{
588 int n = 0;
589
590 if (poly->c[0])
591 /* poly[X] = bX+c with c!=0, root=c/b */
592 roots[n++] = mod_s(bch, GF_N(bch)-bch->a_log_tab[poly->c[0]]+
593 bch->a_log_tab[poly->c[1]]);
594 return n;
595}
596
597/*
598 * compute roots of a degree 2 polynomial over GF(2^m)
599 */
600static int find_poly_deg2_roots(struct bch_control *bch, struct gf_poly *poly,
601 unsigned int *roots)
602{
603 int n = 0, i, l0, l1, l2;
604 unsigned int u, v, r;
605
606 if (poly->c[0] && poly->c[1]) {
607
608 l0 = bch->a_log_tab[poly->c[0]];
609 l1 = bch->a_log_tab[poly->c[1]];
610 l2 = bch->a_log_tab[poly->c[2]];
611
612 /* using z=a/bX, transform aX^2+bX+c into z^2+z+u (u=ac/b^2) */
613 u = a_pow(bch, l0+l2+2*(GF_N(bch)-l1));
614 /*
615 * let u = sum(li.a^i) i=0..m-1; then compute r = sum(li.xi):
616 * r^2+r = sum(li.(xi^2+xi)) = sum(li.(a^i+Tr(a^i).a^k)) =
617 * u + sum(li.Tr(a^i).a^k) = u+a^k.Tr(sum(li.a^i)) = u+a^k.Tr(u)
618 * i.e. r and r+1 are roots iff Tr(u)=0
619 */
620 r = 0;
621 v = u;
622 while (v) {
623 i = deg(v);
624 r ^= bch->xi_tab[i];
625 v ^= (1 << i);
626 }
627 /* verify root */
628 if ((gf_sqr(bch, r)^r) == u) {
629 /* reverse z=a/bX transformation and compute log(1/r) */
630 roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
631 bch->a_log_tab[r]+l2);
632 roots[n++] = modulo(bch, 2*GF_N(bch)-l1-
633 bch->a_log_tab[r^1]+l2);
634 }
635 }
636 return n;
637}
638
639/*
640 * compute roots of a degree 3 polynomial over GF(2^m)
641 */
642static int find_poly_deg3_roots(struct bch_control *bch, struct gf_poly *poly,
643 unsigned int *roots)
644{
645 int i, n = 0;
646 unsigned int a, b, c, a2, b2, c2, e3, tmp[4];
647
648 if (poly->c[0]) {
649 /* transform polynomial into monic X^3 + a2X^2 + b2X + c2 */
650 e3 = poly->c[3];
651 c2 = gf_div(bch, poly->c[0], e3);
652 b2 = gf_div(bch, poly->c[1], e3);
653 a2 = gf_div(bch, poly->c[2], e3);
654
655 /* (X+a2)(X^3+a2X^2+b2X+c2) = X^4+aX^2+bX+c (affine) */
656 c = gf_mul(bch, a2, c2); /* c = a2c2 */
657 b = gf_mul(bch, a2, b2)^c2; /* b = a2b2 + c2 */
658 a = gf_sqr(bch, a2)^b2; /* a = a2^2 + b2 */
659
660 /* find the 4 roots of this affine polynomial */
661 if (find_affine4_roots(bch, a, b, c, tmp) == 4) {
662 /* remove a2 from final list of roots */
663 for (i = 0; i < 4; i++) {
664 if (tmp[i] != a2)
665 roots[n++] = a_ilog(bch, tmp[i]);
666 }
667 }
668 }
669 return n;
670}
671
672/*
673 * compute roots of a degree 4 polynomial over GF(2^m)
674 */
675static int find_poly_deg4_roots(struct bch_control *bch, struct gf_poly *poly,
676 unsigned int *roots)
677{
678 int i, l, n = 0;
679 unsigned int a, b, c, d, e = 0, f, a2, b2, c2, e4;
680
681 if (poly->c[0] == 0)
682 return 0;
683
684 /* transform polynomial into monic X^4 + aX^3 + bX^2 + cX + d */
685 e4 = poly->c[4];
686 d = gf_div(bch, poly->c[0], e4);
687 c = gf_div(bch, poly->c[1], e4);
688 b = gf_div(bch, poly->c[2], e4);
689 a = gf_div(bch, poly->c[3], e4);
690
691 /* use Y=1/X transformation to get an affine polynomial */
692 if (a) {
693 /* first, eliminate cX by using z=X+e with ae^2+c=0 */
694 if (c) {
695 /* compute e such that e^2 = c/a */
696 f = gf_div(bch, c, a);
697 l = a_log(bch, f);
698 l += (l & 1) ? GF_N(bch) : 0;
699 e = a_pow(bch, l/2);
700 /*
701 * use transformation z=X+e:
702 * z^4+e^4 + a(z^3+ez^2+e^2z+e^3) + b(z^2+e^2) +cz+ce+d
703 * z^4 + az^3 + (ae+b)z^2 + (ae^2+c)z+e^4+be^2+ae^3+ce+d
704 * z^4 + az^3 + (ae+b)z^2 + e^4+be^2+d
705 * z^4 + az^3 + b'z^2 + d'
706 */
707 d = a_pow(bch, 2*l)^gf_mul(bch, b, f)^d;
708 b = gf_mul(bch, a, e)^b;
709 }
710 /* now, use Y=1/X to get Y^4 + b/dY^2 + a/dY + 1/d */
711 if (d == 0)
712 /* assume all roots have multiplicity 1 */
713 return 0;
714
715 c2 = gf_inv(bch, d);
716 b2 = gf_div(bch, a, d);
717 a2 = gf_div(bch, b, d);
718 } else {
719 /* polynomial is already affine */
720 c2 = d;
721 b2 = c;
722 a2 = b;
723 }
724 /* find the 4 roots of this affine polynomial */
725 if (find_affine4_roots(bch, a2, b2, c2, roots) == 4) {
726 for (i = 0; i < 4; i++) {
727 /* post-process roots (reverse transformations) */
728 f = a ? gf_inv(bch, roots[i]) : roots[i];
729 roots[i] = a_ilog(bch, f^e);
730 }
731 n = 4;
732 }
733 return n;
734}
735
736/*
737 * build monic, log-based representation of a polynomial
738 */
739static void gf_poly_logrep(struct bch_control *bch,
740 const struct gf_poly *a, int *rep)
741{
742 int i, d = a->deg, l = GF_N(bch)-a_log(bch, a->c[a->deg]);
743
744 /* represent 0 values with -1; warning, rep[d] is not set to 1 */
745 for (i = 0; i < d; i++)
746 rep[i] = a->c[i] ? mod_s(bch, a_log(bch, a->c[i])+l) : -1;
747}
748
749/*
750 * compute polynomial Euclidean division remainder in GF(2^m)[X]
751 */
752static void gf_poly_mod(struct bch_control *bch, struct gf_poly *a,
753 const struct gf_poly *b, int *rep)
754{
755 int la, p, m;
756 unsigned int i, j, *c = a->c;
757 const unsigned int d = b->deg;
758
759 if (a->deg < d)
760 return;
761
762 /* reuse or compute log representation of denominator */
763 if (!rep) {
764 rep = bch->cache;
765 gf_poly_logrep(bch, b, rep);
766 }
767
768 for (j = a->deg; j >= d; j--) {
769 if (c[j]) {
770 la = a_log(bch, c[j]);
771 p = j-d;
772 for (i = 0; i < d; i++, p++) {
773 m = rep[i];
774 if (m >= 0)
775 c[p] ^= bch->a_pow_tab[mod_s(bch,
776 m+la)];
777 }
778 }
779 }
780 a->deg = d-1;
781 while (!c[a->deg] && a->deg)
782 a->deg--;
783}
784
785/*
786 * compute polynomial Euclidean division quotient in GF(2^m)[X]
787 */
788static void gf_poly_div(struct bch_control *bch, struct gf_poly *a,
789 const struct gf_poly *b, struct gf_poly *q)
790{
791 if (a->deg >= b->deg) {
792 q->deg = a->deg-b->deg;
793 /* compute a mod b (modifies a) */
794 gf_poly_mod(bch, a, b, NULL);
795 /* quotient is stored in upper part of polynomial a */
796 memcpy(q->c, &a->c[b->deg], (1+q->deg)*sizeof(unsigned int));
797 } else {
798 q->deg = 0;
799 q->c[0] = 0;
800 }
801}
802
803/*
804 * compute polynomial GCD (Greatest Common Divisor) in GF(2^m)[X]
805 */
806static struct gf_poly *gf_poly_gcd(struct bch_control *bch, struct gf_poly *a,
807 struct gf_poly *b)
808{
809 struct gf_poly *tmp;
810
811 dbg("gcd(%s,%s)=", gf_poly_str(a), gf_poly_str(b));
812
813 if (a->deg < b->deg) {
814 tmp = b;
815 b = a;
816 a = tmp;
817 }
818
819 while (b->deg > 0) {
820 gf_poly_mod(bch, a, b, NULL);
821 tmp = b;
822 b = a;
823 a = tmp;
824 }
825
826 dbg("%s\n", gf_poly_str(a));
827
828 return a;
829}
830
831/*
832 * Given a polynomial f and an integer k, compute Tr(a^kX) mod f
833 * This is used in Berlekamp Trace algorithm for splitting polynomials
834 */
835static void compute_trace_bk_mod(struct bch_control *bch, int k,
836 const struct gf_poly *f, struct gf_poly *z,
837 struct gf_poly *out)
838{
839 const int m = GF_M(bch);
840 int i, j;
841
842 /* z contains z^2j mod f */
843 z->deg = 1;
844 z->c[0] = 0;
845 z->c[1] = bch->a_pow_tab[k];
846
847 out->deg = 0;
848 memset(out, 0, GF_POLY_SZ(f->deg));
849
850 /* compute f log representation only once */
851 gf_poly_logrep(bch, f, bch->cache);
852
853 for (i = 0; i < m; i++) {
854 /* add a^(k*2^i)(z^(2^i) mod f) and compute (z^(2^i) mod f)^2 */
855 for (j = z->deg; j >= 0; j--) {
856 out->c[j] ^= z->c[j];
857 z->c[2*j] = gf_sqr(bch, z->c[j]);
858 z->c[2*j+1] = 0;
859 }
860 if (z->deg > out->deg)
861 out->deg = z->deg;
862
863 if (i < m-1) {
864 z->deg *= 2;
865 /* z^(2(i+1)) mod f = (z^(2^i) mod f)^2 mod f */
866 gf_poly_mod(bch, z, f, bch->cache);
867 }
868 }
869 while (!out->c[out->deg] && out->deg)
870 out->deg--;
871
872 dbg("Tr(a^%d.X) mod f = %s\n", k, gf_poly_str(out));
873}
874
875/*
876 * factor a polynomial using Berlekamp Trace algorithm (BTA)
877 */
878static void factor_polynomial(struct bch_control *bch, int k, struct gf_poly *f,
879 struct gf_poly **g, struct gf_poly **h)
880{
881 struct gf_poly *f2 = bch->poly_2t[0];
882 struct gf_poly *q = bch->poly_2t[1];
883 struct gf_poly *tk = bch->poly_2t[2];
884 struct gf_poly *z = bch->poly_2t[3];
885 struct gf_poly *gcd;
886
887 dbg("factoring %s...\n", gf_poly_str(f));
888
889 *g = f;
890 *h = NULL;
891
892 /* tk = Tr(a^k.X) mod f */
893 compute_trace_bk_mod(bch, k, f, z, tk);
894
895 if (tk->deg > 0) {
896 /* compute g = gcd(f, tk) (destructive operation) */
897 gf_poly_copy(f2, f);
898 gcd = gf_poly_gcd(bch, f2, tk);
899 if (gcd->deg < f->deg) {
900 /* compute h=f/gcd(f,tk); this will modify f and q */
901 gf_poly_div(bch, f, gcd, q);
902 /* store g and h in-place (clobbering f) */
903 *h = &((struct gf_poly_deg1 *)f)[gcd->deg].poly;
904 gf_poly_copy(*g, gcd);
905 gf_poly_copy(*h, q);
906 }
907 }
908}
909
910/*
911 * find roots of a polynomial, using BTZ algorithm; see the beginning of this
912 * file for details
913 */
914static int find_poly_roots(struct bch_control *bch, unsigned int k,
915 struct gf_poly *poly, unsigned int *roots)
916{
917 int cnt;
918 struct gf_poly *f1, *f2;
919
920 switch (poly->deg) {
921 /* handle low degree polynomials with ad hoc techniques */
922 case 1:
923 cnt = find_poly_deg1_roots(bch, poly, roots);
924 break;
925 case 2:
926 cnt = find_poly_deg2_roots(bch, poly, roots);
927 break;
928 case 3:
929 cnt = find_poly_deg3_roots(bch, poly, roots);
930 break;
931 case 4:
932 cnt = find_poly_deg4_roots(bch, poly, roots);
933 break;
934 default:
935 /* factor polynomial using Berlekamp Trace Algorithm (BTA) */
936 cnt = 0;
937 if (poly->deg && (k <= GF_M(bch))) {
938 factor_polynomial(bch, k, poly, &f1, &f2);
939 if (f1)
940 cnt += find_poly_roots(bch, k+1, f1, roots);
941 if (f2)
942 cnt += find_poly_roots(bch, k+1, f2, roots+cnt);
943 }
944 break;
945 }
946 return cnt;
947}
948
949#if defined(USE_CHIEN_SEARCH)
950/*
951 * exhaustive root search (Chien) implementation - not used, included only for
952 * reference/comparison tests
953 */
954static int chien_search(struct bch_control *bch, unsigned int len,
955 struct gf_poly *p, unsigned int *roots)
956{
957 int m;
958 unsigned int i, j, syn, syn0, count = 0;
959 const unsigned int k = 8*len+bch->ecc_bits;
960
961 /* use a log-based representation of polynomial */
962 gf_poly_logrep(bch, p, bch->cache);
963 bch->cache[p->deg] = 0;
964 syn0 = gf_div(bch, p->c[0], p->c[p->deg]);
965
966 for (i = GF_N(bch)-k+1; i <= GF_N(bch); i++) {
967 /* compute elp(a^i) */
968 for (j = 1, syn = syn0; j <= p->deg; j++) {
969 m = bch->cache[j];
970 if (m >= 0)
971 syn ^= a_pow(bch, m+j*i);
972 }
973 if (syn == 0) {
974 roots[count++] = GF_N(bch)-i;
975 if (count == p->deg)
976 break;
977 }
978 }
979 return (count == p->deg) ? count : 0;
980}
981#define find_poly_roots(_p, _k, _elp, _loc) chien_search(_p, len, _elp, _loc)
982#endif /* USE_CHIEN_SEARCH */
983
984/**
985 * decode_bch - decode received codeword and find bit error locations
986 * @bch: BCH control structure
987 * @data: received data, ignored if @calc_ecc is provided
988 * @len: data length in bytes, must always be provided
989 * @recv_ecc: received ecc, if NULL then assume it was XORed in @calc_ecc
990 * @calc_ecc: calculated ecc, if NULL then calc_ecc is computed from @data
991 * @syn: hw computed syndrome data (if NULL, syndrome is calculated)
992 * @errloc: output array of error locations
993 *
994 * Returns:
995 * The number of errors found, or -EBADMSG if decoding failed, or -EINVAL if
996 * invalid parameters were provided
997 *
998 * Depending on the available hw BCH support and the need to compute @calc_ecc
999 * separately (using encode_bch()), this function should be called with one of
1000 * the following parameter configurations -
1001 *
1002 * by providing @data and @recv_ecc only:
1003 * decode_bch(@bch, @data, @len, @recv_ecc, NULL, NULL, @errloc)
1004 *
1005 * by providing @recv_ecc and @calc_ecc:
1006 * decode_bch(@bch, NULL, @len, @recv_ecc, @calc_ecc, NULL, @errloc)
1007 *
1008 * by providing ecc = recv_ecc XOR calc_ecc:
1009 * decode_bch(@bch, NULL, @len, NULL, ecc, NULL, @errloc)
1010 *
1011 * by providing syndrome results @syn:
1012 * decode_bch(@bch, NULL, @len, NULL, NULL, @syn, @errloc)
1013 *
1014 * Once decode_bch() has successfully returned with a positive value, error
1015 * locations returned in array @errloc should be interpreted as follows -
1016 *
1017 * if (errloc[n] >= 8*len), then n-th error is located in ecc (no need for
1018 * data correction)
1019 *
1020 * if (errloc[n] < 8*len), then n-th error is located in data and can be
1021 * corrected with statement data[errloc[n]/8] ^= 1 << (errloc[n] % 8);
1022 *
1023 * Note that this function does not perform any data correction by itself, it
1024 * merely indicates error locations.
1025 */
1026int decode_bch(struct bch_control *bch, const uint8_t *data, unsigned int len,
1027 const uint8_t *recv_ecc, const uint8_t *calc_ecc,
1028 const unsigned int *syn, unsigned int *errloc)
1029{
1030 const unsigned int ecc_words = BCH_ECC_WORDS(bch);
1031 unsigned int nbits;
1032 int i, err, nroots;
1033 uint32_t sum;
1034
1035 /* sanity check: make sure data length can be handled */
1036 if (8*len > (bch->n-bch->ecc_bits))
1037 return -EINVAL;
1038
1039 /* if caller does not provide syndromes, compute them */
1040 if (!syn) {
1041 if (!calc_ecc) {
1042 /* compute received data ecc into an internal buffer */
1043 if (!data || !recv_ecc)
1044 return -EINVAL;
1045 encode_bch(bch, data, len, NULL);
1046 } else {
1047 /* load provided calculated ecc */
1048 load_ecc8(bch, bch->ecc_buf, calc_ecc);
1049 }
1050 /* load received ecc or assume it was XORed in calc_ecc */
1051 if (recv_ecc) {
1052 load_ecc8(bch, bch->ecc_buf2, recv_ecc);
1053 /* XOR received and calculated ecc */
1054 for (i = 0, sum = 0; i < (int)ecc_words; i++) {
1055 bch->ecc_buf[i] ^= bch->ecc_buf2[i];
1056 sum |= bch->ecc_buf[i];
1057 }
1058 if (!sum)
1059 /* no error found */
1060 return 0;
1061 }
1062 compute_syndromes(bch, bch->ecc_buf, bch->syn);
1063 syn = bch->syn;
1064 }
1065
1066 err = compute_error_locator_polynomial(bch, syn);
1067 if (err > 0) {
1068 nroots = find_poly_roots(bch, 1, bch->elp, errloc);
1069 if (err != nroots)
1070 err = -1;
1071 }
1072 if (err > 0) {
1073 /* post-process raw error locations for easier correction */
1074 nbits = (len*8)+bch->ecc_bits;
1075 for (i = 0; i < err; i++) {
1076 if (errloc[i] >= nbits) {
1077 err = -1;
1078 break;
1079 }
1080 errloc[i] = nbits-1-errloc[i];
1081 errloc[i] = (errloc[i] & ~7)|(7-(errloc[i] & 7));
1082 }
1083 }
1084 return (err >= 0) ? err : -EBADMSG;
1085}
1086
1087/*
1088 * generate Galois field lookup tables
1089 */
1090static int build_gf_tables(struct bch_control *bch, unsigned int poly)
1091{
1092 unsigned int i, x = 1;
1093 const unsigned int k = 1 << deg(poly);
1094
1095 /* primitive polynomial must be of degree m */
1096 if (k != (1u << GF_M(bch)))
1097 return -1;
1098
1099 for (i = 0; i < GF_N(bch); i++) {
1100 bch->a_pow_tab[i] = x;
1101 bch->a_log_tab[x] = i;
1102 if (i && (x == 1))
1103 /* polynomial is not primitive (a^i=1 with 0<i<2^m-1) */
1104 return -1;
1105 x <<= 1;
1106 if (x & k)
1107 x ^= poly;
1108 }
1109 bch->a_pow_tab[GF_N(bch)] = 1;
1110 bch->a_log_tab[0] = 0;
1111
1112 return 0;
1113}
1114
1115/*
1116 * compute generator polynomial remainder tables for fast encoding
1117 */
1118static void build_mod8_tables(struct bch_control *bch, const uint32_t *g)
1119{
1120 int i, j, b, d;
1121 uint32_t data, hi, lo, *tab;
1122 const int l = BCH_ECC_WORDS(bch);
1123 const int plen = DIV_ROUND_UP(bch->ecc_bits+1, 32);
1124 const int ecclen = DIV_ROUND_UP(bch->ecc_bits, 32);
1125
1126 memset(bch->mod8_tab, 0, 4*256*l*sizeof(*bch->mod8_tab));
1127
1128 for (i = 0; i < 256; i++) {
1129 /* p(X)=i is a small polynomial of weight <= 8 */
1130 for (b = 0; b < 4; b++) {
1131 /* we want to compute (p(X).X^(8*b+deg(g))) mod g(X) */
1132 tab = bch->mod8_tab + (b*256+i)*l;
1133 data = i << (8*b);
1134 while (data) {
1135 d = deg(data);
1136 /* subtract X^d.g(X) from p(X).X^(8*b+deg(g)) */
1137 data ^= g[0] >> (31-d);
1138 for (j = 0; j < ecclen; j++) {
1139 hi = (d < 31) ? g[j] << (d+1) : 0;
1140 lo = (j+1 < plen) ?
1141 g[j+1] >> (31-d) : 0;
1142 tab[j] ^= hi|lo;
1143 }
1144 }
1145 }
1146 }
1147}
1148
1149/*
1150 * build a base for factoring degree 2 polynomials
1151 */
1152static int build_deg2_base(struct bch_control *bch)
1153{
1154 const int m = GF_M(bch);
1155 int i, j, r;
1156 unsigned int sum, x, y, remaining, ak = 0, xi[m];
1157
1158 /* find k s.t. Tr(a^k) = 1 and 0 <= k < m */
1159 for (i = 0; i < m; i++) {
1160 for (j = 0, sum = 0; j < m; j++)
1161 sum ^= a_pow(bch, i*(1 << j));
1162
1163 if (sum) {
1164 ak = bch->a_pow_tab[i];
1165 break;
1166 }
1167 }
1168 /* find xi, i=0..m-1 such that xi^2+xi = a^i+Tr(a^i).a^k */
1169 remaining = m;
1170 memset(xi, 0, sizeof(xi));
1171
1172 for (x = 0; (x <= GF_N(bch)) && remaining; x++) {
1173 y = gf_sqr(bch, x)^x;
1174 for (i = 0; i < 2; i++) {
1175 r = a_log(bch, y);
1176 if (y && (r < m) && !xi[r]) {
1177 bch->xi_tab[r] = x;
1178 xi[r] = 1;
1179 remaining--;
1180 dbg("x%d = %x\n", r, x);
1181 break;
1182 }
1183 y ^= ak;
1184 }
1185 }
1186 /* should not happen but check anyway */
1187 return remaining ? -1 : 0;
1188}
1189
1190static void *bch_alloc(size_t size, int *err)
1191{
1192 void *ptr;
1193
1194 ptr = kmalloc(size, GFP_KERNEL);
1195 if (ptr == NULL)
1196 *err = 1;
1197 return ptr;
1198}
1199
1200/*
1201 * compute generator polynomial for given (m,t) parameters.
1202 */
1203static uint32_t *compute_generator_polynomial(struct bch_control *bch)
1204{
1205 const unsigned int m = GF_M(bch);
1206 const unsigned int t = GF_T(bch);
1207 int n, err = 0;
1208 unsigned int i, j, nbits, r, word, *roots;
1209 struct gf_poly *g;
1210 uint32_t *genpoly;
1211
1212 g = bch_alloc(GF_POLY_SZ(m*t), &err);
1213 roots = bch_alloc((bch->n+1)*sizeof(*roots), &err);
1214 genpoly = bch_alloc(DIV_ROUND_UP(m*t+1, 32)*sizeof(*genpoly), &err);
1215
1216 if (err) {
1217 kfree(genpoly);
1218 genpoly = NULL;
1219 goto finish;
1220 }
1221
1222 /* enumerate all roots of g(X) */
1223 memset(roots , 0, (bch->n+1)*sizeof(*roots));
1224 for (i = 0; i < t; i++) {
1225 for (j = 0, r = 2*i+1; j < m; j++) {
1226 roots[r] = 1;
1227 r = mod_s(bch, 2*r);
1228 }
1229 }
1230 /* build generator polynomial g(X) */
1231 g->deg = 0;
1232 g->c[0] = 1;
1233 for (i = 0; i < GF_N(bch); i++) {
1234 if (roots[i]) {
1235 /* multiply g(X) by (X+root) */
1236 r = bch->a_pow_tab[i];
1237 g->c[g->deg+1] = 1;
1238 for (j = g->deg; j > 0; j--)
1239 g->c[j] = gf_mul(bch, g->c[j], r)^g->c[j-1];
1240
1241 g->c[0] = gf_mul(bch, g->c[0], r);
1242 g->deg++;
1243 }
1244 }
1245 /* store left-justified binary representation of g(X) */
1246 n = g->deg+1;
1247 i = 0;
1248
1249 while (n > 0) {
1250 nbits = (n > 32) ? 32 : n;
1251 for (j = 0, word = 0; j < nbits; j++) {
1252 if (g->c[n-1-j])
1253 word |= 1u << (31-j);
1254 }
1255 genpoly[i++] = word;
1256 n -= nbits;
1257 }
1258 bch->ecc_bits = g->deg;
1259
1260finish:
1261 kfree(g);
1262 kfree(roots);
1263
1264 return genpoly;
1265}
1266
1267/**
1268 * init_bch - initialize a BCH encoder/decoder
1269 * @m: Galois field order, should be in the range 5-15
1270 * @t: maximum error correction capability, in bits
1271 * @prim_poly: user-provided primitive polynomial (or 0 to use default)
1272 *
1273 * Returns:
1274 * a newly allocated BCH control structure if successful, NULL otherwise
1275 *
1276 * This initialization can take some time, as lookup tables are built for fast
1277 * encoding/decoding; make sure not to call this function from a time critical
1278 * path. Usually, init_bch() should be called on module/driver init and
1279 * free_bch() should be called to release memory on exit.
1280 *
1281 * You may provide your own primitive polynomial of degree @m in argument
1282 * @prim_poly, or let init_bch() use its default polynomial.
1283 *
1284 * Once init_bch() has successfully returned a pointer to a newly allocated
1285 * BCH control structure, ecc length in bytes is given by member @ecc_bytes of
1286 * the structure.
1287 */
1288struct bch_control *init_bch(int m, int t, unsigned int prim_poly)
1289{
1290 int err = 0;
1291 unsigned int i, words;
1292 uint32_t *genpoly;
1293 struct bch_control *bch = NULL;
1294
1295 const int min_m = 5;
1296 const int max_m = 15;
1297
1298 /* default primitive polynomials */
1299 static const unsigned int prim_poly_tab[] = {
1300 0x25, 0x43, 0x83, 0x11d, 0x211, 0x409, 0x805, 0x1053, 0x201b,
1301 0x402b, 0x8003,
1302 };
1303
1304#if defined(CONFIG_BCH_CONST_PARAMS)
1305 if ((m != (CONFIG_BCH_CONST_M)) || (t != (CONFIG_BCH_CONST_T))) {
1306 printk(KERN_ERR "bch encoder/decoder was configured to support "
1307 "parameters m=%d, t=%d only!\n",
1308 CONFIG_BCH_CONST_M, CONFIG_BCH_CONST_T);
1309 goto fail;
1310 }
1311#endif
1312 if ((m < min_m) || (m > max_m))
1313 /*
1314 * values of m greater than 15 are not currently supported;
1315 * supporting m > 15 would require changing table base type
1316 * (uint16_t) and a small patch in matrix transposition
1317 */
1318 goto fail;
1319
1320 /* sanity checks */
1321 if ((t < 1) || (m*t >= ((1 << m)-1)))
1322 /* invalid t value */
1323 goto fail;
1324
1325 /* select a primitive polynomial for generating GF(2^m) */
1326 if (prim_poly == 0)
1327 prim_poly = prim_poly_tab[m-min_m];
1328
1329 bch = kzalloc(sizeof(*bch), GFP_KERNEL);
1330 if (bch == NULL)
1331 goto fail;
1332
1333 bch->m = m;
1334 bch->t = t;
1335 bch->n = (1 << m)-1;
1336 words = DIV_ROUND_UP(m*t, 32);
1337 bch->ecc_bytes = DIV_ROUND_UP(m*t, 8);
1338 bch->a_pow_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_pow_tab), &err);
1339 bch->a_log_tab = bch_alloc((1+bch->n)*sizeof(*bch->a_log_tab), &err);
1340 bch->mod8_tab = bch_alloc(words*1024*sizeof(*bch->mod8_tab), &err);
1341 bch->ecc_buf = bch_alloc(words*sizeof(*bch->ecc_buf), &err);
1342 bch->ecc_buf2 = bch_alloc(words*sizeof(*bch->ecc_buf2), &err);
1343 bch->xi_tab = bch_alloc(m*sizeof(*bch->xi_tab), &err);
1344 bch->syn = bch_alloc(2*t*sizeof(*bch->syn), &err);
1345 bch->cache = bch_alloc(2*t*sizeof(*bch->cache), &err);
1346 bch->elp = bch_alloc((t+1)*sizeof(struct gf_poly_deg1), &err);
1347
1348 for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
1349 bch->poly_2t[i] = bch_alloc(GF_POLY_SZ(2*t), &err);
1350
1351 if (err)
1352 goto fail;
1353
1354 err = build_gf_tables(bch, prim_poly);
1355 if (err)
1356 goto fail;
1357
1358 /* use generator polynomial for computing encoding tables */
1359 genpoly = compute_generator_polynomial(bch);
1360 if (genpoly == NULL)
1361 goto fail;
1362
1363 build_mod8_tables(bch, genpoly);
1364 kfree(genpoly);
1365
1366 err = build_deg2_base(bch);
1367 if (err)
1368 goto fail;
1369
1370 return bch;
1371
1372fail:
1373 free_bch(bch);
1374 return NULL;
1375}
1376
1377/**
1378 * free_bch - free the BCH control structure
1379 * @bch: BCH control structure to release
1380 */
1381void free_bch(struct bch_control *bch)
1382{
1383 unsigned int i;
1384
1385 if (bch) {
1386 kfree(bch->a_pow_tab);
1387 kfree(bch->a_log_tab);
1388 kfree(bch->mod8_tab);
1389 kfree(bch->ecc_buf);
1390 kfree(bch->ecc_buf2);
1391 kfree(bch->xi_tab);
1392 kfree(bch->syn);
1393 kfree(bch->cache);
1394 kfree(bch->elp);
1395
1396 for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
1397 kfree(bch->poly_2t[i]);
1398
1399 kfree(bch);
1400 }
1401}