1 /*
2 * This file provides ECC correction for more than 1 bit per block of data,
3 * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
4 *
5 * Copyright © 2011 Ivan Djelic <ivan.djelic@parrot.com>
6 *
7 * This file is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License as published by the
9 * Free Software Foundation; either version 2 or (at your option) any
10 * later version.
11 *
12 * This file is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * for more details.
16 *
17 * You should have received a copy of the GNU General Public License along
18 * with this file; if not, write to the Free Software Foundation, Inc.,
19 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
20 */
21
22 #include <linux/types.h>
23 #include <linux/kernel.h>
24 #include <linux/module.h>
25 #include <linux/slab.h>
26 #include <linux/bitops.h>
27 #include <linux/mtd/mtd.h>
28 #include <linux/mtd/nand.h>
29 #include <linux/mtd/nand_bch.h>
30 #include <linux/bch.h>
31
32 /**
33 * struct nand_bch_control - private NAND BCH control structure
34 * @bch: BCH control structure
35 * @ecclayout: private ecc layout for this BCH configuration
36 * @errloc: error location array
37 * @eccmask: XOR ecc mask, allows erased pages to be decoded as valid
38 */
39 struct nand_bch_control {
40 struct bch_control *bch;
41 struct nand_ecclayout ecclayout;
42 unsigned int *errloc;
43 unsigned char *eccmask;
44 };
45
46 /**
47 * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
48 * @mtd: MTD block structure
49 * @buf: input buffer with raw data
50 * @code: output buffer with ECC
51 */
nand_bch_calculate_ecc(struct mtd_info * mtd,const unsigned char * buf,unsigned char * code)52 int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
53 unsigned char *code)
54 {
55 const struct nand_chip *chip = mtd->priv;
56 struct nand_bch_control *nbc = chip->ecc.priv;
57 unsigned int i;
58
59 memset(code, 0, chip->ecc.bytes);
60 encode_bch(nbc->bch, buf, chip->ecc.size, code);
61
62 /* apply mask so that an erased page is a valid codeword */
63 for (i = 0; i < chip->ecc.bytes; i++)
64 code[i] ^= nbc->eccmask[i];
65
66 return 0;
67 }
68 EXPORT_SYMBOL(nand_bch_calculate_ecc);
69
70 /**
71 * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
72 * @mtd: MTD block structure
73 * @buf: raw data read from the chip
74 * @read_ecc: ECC from the chip
75 * @calc_ecc: the ECC calculated from raw data
76 *
77 * Detect and correct bit errors for a data byte block
78 */
nand_bch_correct_data(struct mtd_info * mtd,unsigned char * buf,unsigned char * read_ecc,unsigned char * calc_ecc)79 int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
80 unsigned char *read_ecc, unsigned char *calc_ecc)
81 {
82 const struct nand_chip *chip = mtd->priv;
83 struct nand_bch_control *nbc = chip->ecc.priv;
84 unsigned int *errloc = nbc->errloc;
85 int i, count;
86
87 count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
88 NULL, errloc);
89 if (count > 0) {
90 for (i = 0; i < count; i++) {
91 if (errloc[i] < (chip->ecc.size*8))
92 /* error is located in data, correct it */
93 buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
94 /* else error in ecc, no action needed */
95
96 pr_debug("%s: corrected bitflip %u\n", __func__,
97 errloc[i]);
98 }
99 } else if (count < 0) {
100 printk(KERN_ERR "ecc unrecoverable error\n");
101 count = -1;
102 }
103 return count;
104 }
105 EXPORT_SYMBOL(nand_bch_correct_data);
106
107 /**
108 * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
109 * @mtd: MTD block structure
110 * @eccsize: ecc block size in bytes
111 * @eccbytes: ecc length in bytes
112 * @ecclayout: output default layout
113 *
114 * Returns:
115 * a pointer to a new NAND BCH control structure, or NULL upon failure
116 *
117 * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
118 * are used to compute BCH parameters m (Galois field order) and t (error
119 * correction capability). @eccbytes should be equal to the number of bytes
120 * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
121 *
122 * Example: to configure 4 bit correction per 512 bytes, you should pass
123 * @eccsize = 512 (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
124 * @eccbytes = 7 (7 bytes are required to store m*t = 13*4 = 52 bits)
125 */
126 struct nand_bch_control *
nand_bch_init(struct mtd_info * mtd,unsigned int eccsize,unsigned int eccbytes,struct nand_ecclayout ** ecclayout)127 nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
128 struct nand_ecclayout **ecclayout)
129 {
130 unsigned int m, t, eccsteps, i;
131 struct nand_ecclayout *layout;
132 struct nand_bch_control *nbc = NULL;
133 unsigned char *erased_page;
134
135 if (!eccsize || !eccbytes) {
136 printk(KERN_WARNING "ecc parameters not supplied\n");
137 goto fail;
138 }
139
140 m = fls(1+8*eccsize);
141 t = (eccbytes*8)/m;
142
143 nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
144 if (!nbc)
145 goto fail;
146
147 nbc->bch = init_bch(m, t, 0);
148 if (!nbc->bch)
149 goto fail;
150
151 /* verify that eccbytes has the expected value */
152 if (nbc->bch->ecc_bytes != eccbytes) {
153 printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
154 eccbytes, nbc->bch->ecc_bytes);
155 goto fail;
156 }
157
158 eccsteps = mtd->writesize/eccsize;
159
160 /* if no ecc placement scheme was provided, build one */
161 if (!*ecclayout) {
162
163 /* handle large page devices only */
164 if (mtd->oobsize < 64) {
165 printk(KERN_WARNING "must provide an oob scheme for "
166 "oobsize %d\n", mtd->oobsize);
167 goto fail;
168 }
169
170 layout = &nbc->ecclayout;
171 layout->eccbytes = eccsteps*eccbytes;
172
173 /* reserve 2 bytes for bad block marker */
174 if (layout->eccbytes+2 > mtd->oobsize) {
175 printk(KERN_WARNING "no suitable oob scheme available "
176 "for oobsize %d eccbytes %u\n", mtd->oobsize,
177 eccbytes);
178 goto fail;
179 }
180 /* put ecc bytes at oob tail */
181 for (i = 0; i < layout->eccbytes; i++)
182 layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
183
184 layout->oobfree[0].offset = 2;
185 layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
186
187 *ecclayout = layout;
188 }
189
190 /* sanity checks */
191 if (8*(eccsize+eccbytes) >= (1 << m)) {
192 printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
193 goto fail;
194 }
195 if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
196 printk(KERN_WARNING "invalid ecc layout\n");
197 goto fail;
198 }
199
200 nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
201 nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
202 if (!nbc->eccmask || !nbc->errloc)
203 goto fail;
204 /*
205 * compute and store the inverted ecc of an erased ecc block
206 */
207 erased_page = kmalloc(eccsize, GFP_KERNEL);
208 if (!erased_page)
209 goto fail;
210
211 memset(erased_page, 0xff, eccsize);
212 memset(nbc->eccmask, 0, eccbytes);
213 encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
214 kfree(erased_page);
215
216 for (i = 0; i < eccbytes; i++)
217 nbc->eccmask[i] ^= 0xff;
218
219 return nbc;
220 fail:
221 nand_bch_free(nbc);
222 return NULL;
223 }
224 EXPORT_SYMBOL(nand_bch_init);
225
226 /**
227 * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
228 * @nbc: NAND BCH control structure
229 */
nand_bch_free(struct nand_bch_control * nbc)230 void nand_bch_free(struct nand_bch_control *nbc)
231 {
232 if (nbc) {
233 free_bch(nbc->bch);
234 kfree(nbc->errloc);
235 kfree(nbc->eccmask);
236 kfree(nbc);
237 }
238 }
239 EXPORT_SYMBOL(nand_bch_free);
240
241 MODULE_LICENSE("GPL");
242 MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
243 MODULE_DESCRIPTION("NAND software BCH ECC support");
244