2
* This file contains an ECC algorithm that detects and corrects 1 bit
3
* errors in a 256 byte block of data.
5
* drivers/mtd/nand/nand_ecc.c
7
* Copyright Ā© 2008 Koninklijke Philips Electronics NV.
8
* Author: Frans Meulenbroeks
10
* Completely replaces the previous ECC implementation which was written by:
11
* Steven J. Hill (sjhill@realitydiluted.com)
12
* Thomas Gleixner (tglx@linutronix.de)
14
* Information on how this algorithm works and how it was developed
15
* can be found in Documentation/mtd/nand_ecc.txt
17
* This file is free software; you can redistribute it and/or modify it
18
* under the terms of the GNU General Public License as published by the
19
* Free Software Foundation; either version 2 or (at your option) any
22
* This file is distributed in the hope that it will be useful, but WITHOUT
23
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
24
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
27
* You should have received a copy of the GNU General Public License along
28
* with this file; if not, write to the Free Software Foundation, Inc.,
29
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
34
* The STANDALONE macro is useful when running the code outside the kernel
35
* e.g. when running the code in a testbed or a benchmark program.
36
* When STANDALONE is used, the module related macros are commented out
37
* as well as the linux include files.
38
* Instead a private definition of mtd_info is given to satisfy the compiler
39
* (the code does not use mtd_info, so the code does not care)
42
#include <linux/types.h>
43
#include <linux/kernel.h>
44
#include <linux/module.h>
45
#include <linux/mtd/mtd.h>
46
#include <linux/mtd/nand.h>
47
#include <linux/mtd/nand_ecc.h>
48
#include <asm/byteorder.h>
52
#define EXPORT_SYMBOL(x) /* x */
54
#define MODULE_LICENSE(x) /* x */
55
#define MODULE_AUTHOR(x) /* x */
56
#define MODULE_DESCRIPTION(x) /* x */
63
* invparity is a 256 byte table that contains the odd parity
64
* for each byte. So if the number of bits in a byte is even,
65
* the array element is 1, and when the number of bits is odd
66
* the array eleemnt is 0.
68
static const char invparity[256] = {
69
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
70
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
71
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
72
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
73
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
74
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
75
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
76
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
77
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
78
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
79
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
80
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
81
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1,
82
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
83
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0,
84
1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1
88
* bitsperbyte contains the number of bits per byte
89
* this is only used for testing and repairing parity
90
* (a precalculated value slightly improves performance)
92
static const char bitsperbyte[256] = {
93
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
94
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
95
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
96
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
97
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
98
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
99
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
100
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
101
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
102
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
103
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
104
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
105
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
106
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
107
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
108
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
112
* addressbits is a lookup table to filter out the bits from the xor-ed
113
* ECC data that identify the faulty location.
114
* this is only used for repairing parity
115
* see the comments in nand_correct_data for more details
117
static const char addressbits[256] = {
118
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
119
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
120
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
121
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
122
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
123
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
124
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
125
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
126
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
127
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
128
0x00, 0x00, 0x01, 0x01, 0x00, 0x00, 0x01, 0x01,
129
0x02, 0x02, 0x03, 0x03, 0x02, 0x02, 0x03, 0x03,
130
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
131
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
132
0x04, 0x04, 0x05, 0x05, 0x04, 0x04, 0x05, 0x05,
133
0x06, 0x06, 0x07, 0x07, 0x06, 0x06, 0x07, 0x07,
134
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
135
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
136
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
137
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
138
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
139
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
140
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
141
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
142
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
143
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
144
0x08, 0x08, 0x09, 0x09, 0x08, 0x08, 0x09, 0x09,
145
0x0a, 0x0a, 0x0b, 0x0b, 0x0a, 0x0a, 0x0b, 0x0b,
146
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
147
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f,
148
0x0c, 0x0c, 0x0d, 0x0d, 0x0c, 0x0c, 0x0d, 0x0d,
149
0x0e, 0x0e, 0x0f, 0x0f, 0x0e, 0x0e, 0x0f, 0x0f
153
* __nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
155
* @buf: input buffer with raw data
156
* @eccsize: data bytes per ECC step (256 or 512)
157
* @code: output buffer with ECC
159
void __nand_calculate_ecc(const unsigned char *buf, unsigned int eccsize,
163
const uint32_t *bp = (uint32_t *)buf;
164
/* 256 or 512 bytes/ecc */
165
const uint32_t eccsize_mult = eccsize >> 8;
166
uint32_t cur; /* current value in buffer */
167
/* rp0..rp15..rp17 are the various accumulated parities (per byte) */
168
uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
169
uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
170
uint32_t uninitialized_var(rp17); /* to make compiler happy */
171
uint32_t par; /* the cumulative parity for all data */
172
uint32_t tmppar; /* the cumulative parity for this iteration;
173
for rp12, rp14 and rp16 at the end of the
186
* The loop is unrolled a number of times;
187
* This avoids if statements to decide on which rp value to update
188
* Also we process the data by longwords.
189
* Note: passing unaligned data might give a performance penalty.
190
* It is assumed that the buffers are aligned.
191
* tmppar is the cumulative sum of this iteration.
192
* needed for calculating rp12, rp14, rp16 and par
193
* also used as a performance improvement for rp6, rp8 and rp10
195
for (i = 0; i < eccsize_mult << 2; i++) {
258
if (eccsize_mult == 2 && (i & 0x4) == 0)
263
* handle the fact that we use longword operations
264
* we'll bring rp4..rp14..rp16 back to single byte entities by
265
* shifting and xoring first fold the upper and lower 16 bits,
266
* then the upper and lower 8 bits.
277
rp10 ^= (rp10 >> 16);
280
rp12 ^= (rp12 >> 16);
283
rp14 ^= (rp14 >> 16);
286
if (eccsize_mult == 2) {
287
rp16 ^= (rp16 >> 16);
293
* we also need to calculate the row parity for rp0..rp3
294
* This is present in par, because par is now
295
* rp3 rp3 rp2 rp2 in little endian and
296
* rp2 rp2 rp3 rp3 in big endian
298
* rp1 rp0 rp1 rp0 in little endian and
299
* rp0 rp1 rp0 rp1 in big endian
300
* First calculate rp2 and rp3
318
/* reduce par to 16 bits then calculate rp1 and rp0 */
321
rp0 = (par >> 8) & 0xff;
324
rp1 = (par >> 8) & 0xff;
328
/* finally reduce par to 8 bits */
333
* and calculate rp5..rp15..rp17
334
* note that par = rp4 ^ rp5 and due to the commutative property
335
* of the ^ operator we can say:
337
* The & 0xff seems superfluous, but benchmarking learned that
338
* leaving it out gives slightly worse results. No idea why, probably
339
* it has to do with the way the pipeline in pentium is organized.
341
rp5 = (par ^ rp4) & 0xff;
342
rp7 = (par ^ rp6) & 0xff;
343
rp9 = (par ^ rp8) & 0xff;
344
rp11 = (par ^ rp10) & 0xff;
345
rp13 = (par ^ rp12) & 0xff;
346
rp15 = (par ^ rp14) & 0xff;
347
if (eccsize_mult == 2)
348
rp17 = (par ^ rp16) & 0xff;
351
* Finally calculate the ECC bits.
352
* Again here it might seem that there are performance optimisations
353
* possible, but benchmarks showed that on the system this is developed
354
* the code below is the fastest
356
#ifdef CONFIG_MTD_NAND_ECC_SMC
358
(invparity[rp7] << 7) |
359
(invparity[rp6] << 6) |
360
(invparity[rp5] << 5) |
361
(invparity[rp4] << 4) |
362
(invparity[rp3] << 3) |
363
(invparity[rp2] << 2) |
364
(invparity[rp1] << 1) |
367
(invparity[rp15] << 7) |
368
(invparity[rp14] << 6) |
369
(invparity[rp13] << 5) |
370
(invparity[rp12] << 4) |
371
(invparity[rp11] << 3) |
372
(invparity[rp10] << 2) |
373
(invparity[rp9] << 1) |
377
(invparity[rp7] << 7) |
378
(invparity[rp6] << 6) |
379
(invparity[rp5] << 5) |
380
(invparity[rp4] << 4) |
381
(invparity[rp3] << 3) |
382
(invparity[rp2] << 2) |
383
(invparity[rp1] << 1) |
386
(invparity[rp15] << 7) |
387
(invparity[rp14] << 6) |
388
(invparity[rp13] << 5) |
389
(invparity[rp12] << 4) |
390
(invparity[rp11] << 3) |
391
(invparity[rp10] << 2) |
392
(invparity[rp9] << 1) |
395
if (eccsize_mult == 1)
397
(invparity[par & 0xf0] << 7) |
398
(invparity[par & 0x0f] << 6) |
399
(invparity[par & 0xcc] << 5) |
400
(invparity[par & 0x33] << 4) |
401
(invparity[par & 0xaa] << 3) |
402
(invparity[par & 0x55] << 2) |
406
(invparity[par & 0xf0] << 7) |
407
(invparity[par & 0x0f] << 6) |
408
(invparity[par & 0xcc] << 5) |
409
(invparity[par & 0x33] << 4) |
410
(invparity[par & 0xaa] << 3) |
411
(invparity[par & 0x55] << 2) |
412
(invparity[rp17] << 1) |
413
(invparity[rp16] << 0);
415
EXPORT_SYMBOL(__nand_calculate_ecc);
418
* nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
420
* @mtd: MTD block structure
421
* @buf: input buffer with raw data
422
* @code: output buffer with ECC
424
int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
427
__nand_calculate_ecc(buf,
428
((struct nand_chip *)mtd->priv)->ecc.size, code);
432
EXPORT_SYMBOL(nand_calculate_ecc);
435
* __nand_correct_data - [NAND Interface] Detect and correct bit error(s)
436
* @buf: raw data read from the chip
437
* @read_ecc: ECC from the chip
438
* @calc_ecc: the ECC calculated from raw data
439
* @eccsize: data bytes per ECC step (256 or 512)
441
* Detect and correct a 1 bit error for eccsize byte block
443
int __nand_correct_data(unsigned char *buf,
444
unsigned char *read_ecc, unsigned char *calc_ecc,
445
unsigned int eccsize)
447
unsigned char b0, b1, b2, bit_addr;
448
unsigned int byte_addr;
449
/* 256 or 512 bytes/ecc */
450
const uint32_t eccsize_mult = eccsize >> 8;
453
* b0 to b2 indicate which bit is faulty (if any)
454
* we might need the xor result more than once,
455
* so keep them in a local var
457
#ifdef CONFIG_MTD_NAND_ECC_SMC
458
b0 = read_ecc[0] ^ calc_ecc[0];
459
b1 = read_ecc[1] ^ calc_ecc[1];
461
b0 = read_ecc[1] ^ calc_ecc[1];
462
b1 = read_ecc[0] ^ calc_ecc[0];
464
b2 = read_ecc[2] ^ calc_ecc[2];
466
/* check if there are any bitfaults */
468
/* repeated if statements are slightly more efficient than switch ... */
469
/* ordered in order of likelihood */
471
if ((b0 | b1 | b2) == 0)
472
return 0; /* no error */
474
if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
475
(((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
476
((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
477
(eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
478
/* single bit error */
480
* rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
481
* byte, cp 5/3/1 indicate the faulty bit.
482
* A lookup table (called addressbits) is used to filter
483
* the bits from the byte they are in.
484
* A marginal optimisation is possible by having three
485
* different lookup tables.
486
* One as we have now (for b0), one for b2
487
* (that would avoid the >> 1), and one for b1 (with all values
488
* << 4). However it was felt that introducing two more tables
489
* hardly justify the gain.
491
* The b2 shift is there to get rid of the lowest two bits.
492
* We could also do addressbits[b2] >> 1 but for the
493
* performance it does not make any difference
495
if (eccsize_mult == 1)
496
byte_addr = (addressbits[b1] << 4) + addressbits[b0];
498
byte_addr = (addressbits[b2 & 0x3] << 8) +
499
(addressbits[b1] << 4) + addressbits[b0];
500
bit_addr = addressbits[b2 >> 2];
502
buf[byte_addr] ^= (1 << bit_addr);
506
/* count nr of bits; use table lookup, faster than calculating it */
507
if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
508
return 1; /* error in ECC data; no action needed */
510
printk(KERN_ERR "uncorrectable error : ");
513
EXPORT_SYMBOL(__nand_correct_data);
516
* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
517
* @mtd: MTD block structure
518
* @buf: raw data read from the chip
519
* @read_ecc: ECC from the chip
520
* @calc_ecc: the ECC calculated from raw data
522
* Detect and correct a 1 bit error for 256/512 byte block
524
int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
525
unsigned char *read_ecc, unsigned char *calc_ecc)
527
return __nand_correct_data(buf, read_ecc, calc_ecc,
528
((struct nand_chip *)mtd->priv)->ecc.size);
530
EXPORT_SYMBOL(nand_correct_data);
532
MODULE_LICENSE("GPL");
533
MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
534
MODULE_DESCRIPTION("Generic NAND ECC support");