1 /*
2 * This file contains an ECC algorithm that detects and corrects 1 bit
3 * errors in a 256 byte block of data.
4 *
5 * drivers/mtd/nand/nand_ecc.c
6 *
7 * Copyright © 2008 Koninklijke Philips Electronics NV.
8 * Author: Frans Meulenbroeks
9 *
10 * Completely replaces the previous ECC implementation which was written by:
11 * Steven J. Hill (sjhill@realitydiluted.com)
12 * Thomas Gleixner (tglx@linutronix.de)
13 *
14 * Information on how this algorithm works and how it was developed
15 * can be found in Documentation/mtd/nand_ecc.txt
16 *
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
20 * later version.
21 *
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
25 * for more details.
26 *
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.
30 *
31 */
32
33 /*
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)
40 */
41 #ifndef STANDALONE
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>
49 #else
50 #include <stdint.h>
51 struct mtd_info;
52 #define EXPORT_SYMBOL(x) /* x */
53
54 #define MODULE_LICENSE(x) /* x */
55 #define MODULE_AUTHOR(x) /* x */
56 #define MODULE_DESCRIPTION(x) /* x */
57
58 #define printk printf
59 #define KERN_ERR ""
60 #endif
61
62 /*
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.
67 */
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
85 };
86
87 /*
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)
91 */
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,
109 };
110
111 /*
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
116 */
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
150 };
151
152 /**
153 * nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
154 * block
155 * @mtd: MTD block structure
156 * @buf: input buffer with raw data
157 * @code: output buffer with ECC
158 */
nand_calculate_ecc(struct mtd_info * mtd,const unsigned char * buf,unsigned char * code)159 int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
160 unsigned char *code)
161 {
162 int i;
163 const uint32_t *bp = (uint32_t *)buf;
164 /* 256 or 512 bytes/ecc */
165 const uint32_t eccsize_mult =
166 (((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
167 uint32_t cur; /* current value in buffer */
168 /* rp0..rp15..rp17 are the various accumulated parities (per byte) */
169 uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
170 uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
171 uint32_t uninitialized_var(rp17); /* to make compiler happy */
172 uint32_t par; /* the cumulative parity for all data */
173 uint32_t tmppar; /* the cumulative parity for this iteration;
174 for rp12, rp14 and rp16 at the end of the
175 loop */
176
177 par = 0;
178 rp4 = 0;
179 rp6 = 0;
180 rp8 = 0;
181 rp10 = 0;
182 rp12 = 0;
183 rp14 = 0;
184 rp16 = 0;
185
186 /*
187 * The loop is unrolled a number of times;
188 * This avoids if statements to decide on which rp value to update
189 * Also we process the data by longwords.
190 * Note: passing unaligned data might give a performance penalty.
191 * It is assumed that the buffers are aligned.
192 * tmppar is the cumulative sum of this iteration.
193 * needed for calculating rp12, rp14, rp16 and par
194 * also used as a performance improvement for rp6, rp8 and rp10
195 */
196 for (i = 0; i < eccsize_mult << 2; i++) {
197 cur = *bp++;
198 tmppar = cur;
199 rp4 ^= cur;
200 cur = *bp++;
201 tmppar ^= cur;
202 rp6 ^= tmppar;
203 cur = *bp++;
204 tmppar ^= cur;
205 rp4 ^= cur;
206 cur = *bp++;
207 tmppar ^= cur;
208 rp8 ^= tmppar;
209
210 cur = *bp++;
211 tmppar ^= cur;
212 rp4 ^= cur;
213 rp6 ^= cur;
214 cur = *bp++;
215 tmppar ^= cur;
216 rp6 ^= cur;
217 cur = *bp++;
218 tmppar ^= cur;
219 rp4 ^= cur;
220 cur = *bp++;
221 tmppar ^= cur;
222 rp10 ^= tmppar;
223
224 cur = *bp++;
225 tmppar ^= cur;
226 rp4 ^= cur;
227 rp6 ^= cur;
228 rp8 ^= cur;
229 cur = *bp++;
230 tmppar ^= cur;
231 rp6 ^= cur;
232 rp8 ^= cur;
233 cur = *bp++;
234 tmppar ^= cur;
235 rp4 ^= cur;
236 rp8 ^= cur;
237 cur = *bp++;
238 tmppar ^= cur;
239 rp8 ^= cur;
240
241 cur = *bp++;
242 tmppar ^= cur;
243 rp4 ^= cur;
244 rp6 ^= cur;
245 cur = *bp++;
246 tmppar ^= cur;
247 rp6 ^= cur;
248 cur = *bp++;
249 tmppar ^= cur;
250 rp4 ^= cur;
251 cur = *bp++;
252 tmppar ^= cur;
253
254 par ^= tmppar;
255 if ((i & 0x1) == 0)
256 rp12 ^= tmppar;
257 if ((i & 0x2) == 0)
258 rp14 ^= tmppar;
259 if (eccsize_mult == 2 && (i & 0x4) == 0)
260 rp16 ^= tmppar;
261 }
262
263 /*
264 * handle the fact that we use longword operations
265 * we'll bring rp4..rp14..rp16 back to single byte entities by
266 * shifting and xoring first fold the upper and lower 16 bits,
267 * then the upper and lower 8 bits.
268 */
269 rp4 ^= (rp4 >> 16);
270 rp4 ^= (rp4 >> 8);
271 rp4 &= 0xff;
272 rp6 ^= (rp6 >> 16);
273 rp6 ^= (rp6 >> 8);
274 rp6 &= 0xff;
275 rp8 ^= (rp8 >> 16);
276 rp8 ^= (rp8 >> 8);
277 rp8 &= 0xff;
278 rp10 ^= (rp10 >> 16);
279 rp10 ^= (rp10 >> 8);
280 rp10 &= 0xff;
281 rp12 ^= (rp12 >> 16);
282 rp12 ^= (rp12 >> 8);
283 rp12 &= 0xff;
284 rp14 ^= (rp14 >> 16);
285 rp14 ^= (rp14 >> 8);
286 rp14 &= 0xff;
287 if (eccsize_mult == 2) {
288 rp16 ^= (rp16 >> 16);
289 rp16 ^= (rp16 >> 8);
290 rp16 &= 0xff;
291 }
292
293 /*
294 * we also need to calculate the row parity for rp0..rp3
295 * This is present in par, because par is now
296 * rp3 rp3 rp2 rp2 in little endian and
297 * rp2 rp2 rp3 rp3 in big endian
298 * as well as
299 * rp1 rp0 rp1 rp0 in little endian and
300 * rp0 rp1 rp0 rp1 in big endian
301 * First calculate rp2 and rp3
302 */
303 #ifdef __BIG_ENDIAN
304 rp2 = (par >> 16);
305 rp2 ^= (rp2 >> 8);
306 rp2 &= 0xff;
307 rp3 = par & 0xffff;
308 rp3 ^= (rp3 >> 8);
309 rp3 &= 0xff;
310 #else
311 rp3 = (par >> 16);
312 rp3 ^= (rp3 >> 8);
313 rp3 &= 0xff;
314 rp2 = par & 0xffff;
315 rp2 ^= (rp2 >> 8);
316 rp2 &= 0xff;
317 #endif
318
319 /* reduce par to 16 bits then calculate rp1 and rp0 */
320 par ^= (par >> 16);
321 #ifdef __BIG_ENDIAN
322 rp0 = (par >> 8) & 0xff;
323 rp1 = (par & 0xff);
324 #else
325 rp1 = (par >> 8) & 0xff;
326 rp0 = (par & 0xff);
327 #endif
328
329 /* finally reduce par to 8 bits */
330 par ^= (par >> 8);
331 par &= 0xff;
332
333 /*
334 * and calculate rp5..rp15..rp17
335 * note that par = rp4 ^ rp5 and due to the commutative property
336 * of the ^ operator we can say:
337 * rp5 = (par ^ rp4);
338 * The & 0xff seems superfluous, but benchmarking learned that
339 * leaving it out gives slightly worse results. No idea why, probably
340 * it has to do with the way the pipeline in pentium is organized.
341 */
342 rp5 = (par ^ rp4) & 0xff;
343 rp7 = (par ^ rp6) & 0xff;
344 rp9 = (par ^ rp8) & 0xff;
345 rp11 = (par ^ rp10) & 0xff;
346 rp13 = (par ^ rp12) & 0xff;
347 rp15 = (par ^ rp14) & 0xff;
348 if (eccsize_mult == 2)
349 rp17 = (par ^ rp16) & 0xff;
350
351 /*
352 * Finally calculate the ecc bits.
353 * Again here it might seem that there are performance optimisations
354 * possible, but benchmarks showed that on the system this is developed
355 * the code below is the fastest
356 */
357 #ifdef CONFIG_MTD_NAND_ECC_SMC
358 code[0] =
359 (invparity[rp7] << 7) |
360 (invparity[rp6] << 6) |
361 (invparity[rp5] << 5) |
362 (invparity[rp4] << 4) |
363 (invparity[rp3] << 3) |
364 (invparity[rp2] << 2) |
365 (invparity[rp1] << 1) |
366 (invparity[rp0]);
367 code[1] =
368 (invparity[rp15] << 7) |
369 (invparity[rp14] << 6) |
370 (invparity[rp13] << 5) |
371 (invparity[rp12] << 4) |
372 (invparity[rp11] << 3) |
373 (invparity[rp10] << 2) |
374 (invparity[rp9] << 1) |
375 (invparity[rp8]);
376 #else
377 code[1] =
378 (invparity[rp7] << 7) |
379 (invparity[rp6] << 6) |
380 (invparity[rp5] << 5) |
381 (invparity[rp4] << 4) |
382 (invparity[rp3] << 3) |
383 (invparity[rp2] << 2) |
384 (invparity[rp1] << 1) |
385 (invparity[rp0]);
386 code[0] =
387 (invparity[rp15] << 7) |
388 (invparity[rp14] << 6) |
389 (invparity[rp13] << 5) |
390 (invparity[rp12] << 4) |
391 (invparity[rp11] << 3) |
392 (invparity[rp10] << 2) |
393 (invparity[rp9] << 1) |
394 (invparity[rp8]);
395 #endif
396 if (eccsize_mult == 1)
397 code[2] =
398 (invparity[par & 0xf0] << 7) |
399 (invparity[par & 0x0f] << 6) |
400 (invparity[par & 0xcc] << 5) |
401 (invparity[par & 0x33] << 4) |
402 (invparity[par & 0xaa] << 3) |
403 (invparity[par & 0x55] << 2) |
404 3;
405 else
406 code[2] =
407 (invparity[par & 0xf0] << 7) |
408 (invparity[par & 0x0f] << 6) |
409 (invparity[par & 0xcc] << 5) |
410 (invparity[par & 0x33] << 4) |
411 (invparity[par & 0xaa] << 3) |
412 (invparity[par & 0x55] << 2) |
413 (invparity[rp17] << 1) |
414 (invparity[rp16] << 0);
415 return 0;
416 }
417 EXPORT_SYMBOL(nand_calculate_ecc);
418
419 /**
420 * nand_correct_data - [NAND Interface] Detect and correct bit error(s)
421 * @mtd: MTD block structure
422 * @buf: raw data read from the chip
423 * @read_ecc: ECC from the chip
424 * @calc_ecc: the ECC calculated from raw data
425 *
426 * Detect and correct a 1 bit error for 256/512 byte block
427 */
nand_correct_data(struct mtd_info * mtd,unsigned char * buf,unsigned char * read_ecc,unsigned char * calc_ecc)428 int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
429 unsigned char *read_ecc, unsigned char *calc_ecc)
430 {
431 unsigned char b0, b1, b2;
432 unsigned char byte_addr, bit_addr;
433 /* 256 or 512 bytes/ecc */
434 const uint32_t eccsize_mult =
435 (((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
436
437 /*
438 * b0 to b2 indicate which bit is faulty (if any)
439 * we might need the xor result more than once,
440 * so keep them in a local var
441 */
442 #ifdef CONFIG_MTD_NAND_ECC_SMC
443 b0 = read_ecc[0] ^ calc_ecc[0];
444 b1 = read_ecc[1] ^ calc_ecc[1];
445 #else
446 b0 = read_ecc[1] ^ calc_ecc[1];
447 b1 = read_ecc[0] ^ calc_ecc[0];
448 #endif
449 b2 = read_ecc[2] ^ calc_ecc[2];
450
451 /* check if there are any bitfaults */
452
453 /* repeated if statements are slightly more efficient than switch ... */
454 /* ordered in order of likelihood */
455
456 if ((b0 | b1 | b2) == 0)
457 return 0; /* no error */
458
459 if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
460 (((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
461 ((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
462 (eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
463 /* single bit error */
464 /*
465 * rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
466 * byte, cp 5/3/1 indicate the faulty bit.
467 * A lookup table (called addressbits) is used to filter
468 * the bits from the byte they are in.
469 * A marginal optimisation is possible by having three
470 * different lookup tables.
471 * One as we have now (for b0), one for b2
472 * (that would avoid the >> 1), and one for b1 (with all values
473 * << 4). However it was felt that introducing two more tables
474 * hardly justify the gain.
475 *
476 * The b2 shift is there to get rid of the lowest two bits.
477 * We could also do addressbits[b2] >> 1 but for the
478 * performace it does not make any difference
479 */
480 if (eccsize_mult == 1)
481 byte_addr = (addressbits[b1] << 4) + addressbits[b0];
482 else
483 byte_addr = (addressbits[b2 & 0x3] << 8) +
484 (addressbits[b1] << 4) + addressbits[b0];
485 bit_addr = addressbits[b2 >> 2];
486 /* flip the bit */
487 buf[byte_addr] ^= (1 << bit_addr);
488 return 1;
489
490 }
491 /* count nr of bits; use table lookup, faster than calculating it */
492 if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
493 return 1; /* error in ecc data; no action needed */
494
495 printk(KERN_ERR "uncorrectable error : ");
496 return -1;
497 }
498 EXPORT_SYMBOL(nand_correct_data);
499
500 MODULE_LICENSE("GPL");
501 MODULE_AUTHOR("Frans Meulenbroeks <fransmeulenbroeks@gmail.com>");
502 MODULE_DESCRIPTION("Generic NAND ECC support");
503