drivers/mtd/nand/nand_bch.c

   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  */
  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_to_nand(mtd);
  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  */
  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_to_nand(mtd);
  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 = -EBADMSG;
 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  *
 111  * Returns:
 112  *  a pointer to a new NAND BCH control structure, or NULL upon failure
 113  *
 114  * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
 115  * are used to compute BCH parameters m (Galois field order) and t (error
 116  * correction capability). @eccbytes should be equal to the number of bytes
 117  * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
 118  *
 119  * Example: to configure 4 bit correction per 512 bytes, you should pass
 120  * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
 121  * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
 122  */
 123 struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
 124 {
 125         struct nand_chip *nand = mtd_to_nand(mtd);
 126         unsigned int m, t, eccsteps, i;
 127         struct nand_ecclayout *layout = nand->ecc.layout;
 128         struct nand_bch_control *nbc = NULL;
 129         unsigned char *erased_page;
 130         unsigned int eccsize = nand->ecc.size;
 131         unsigned int eccbytes = nand->ecc.bytes;
 132         unsigned int eccstrength = nand->ecc.strength;
 133
 134         if (!eccbytes && eccstrength) {
 135                 eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
 136                 nand->ecc.bytes = eccbytes;
 137         }
 138
 139         if (!eccsize || !eccbytes) {
 140                 printk(KERN_WARNING "ecc parameters not supplied\n");
 141                 goto fail;
 142         }
 143
 144         m = fls(1+8*eccsize);
 145         t = (eccbytes*8)/m;
 146
 147         nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
 148         if (!nbc)
 149                 goto fail;
 150
 151         nbc->bch = init_bch(m, t, 0);
 152         if (!nbc->bch)
 153                 goto fail;
 154
 155         /* verify that eccbytes has the expected value */
 156         if (nbc->bch->ecc_bytes != eccbytes) {
 157                 printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
 158                        eccbytes, nbc->bch->ecc_bytes);
 159                 goto fail;
 160         }
 161
 162         eccsteps = mtd->writesize/eccsize;
 163
 164         /* if no ecc placement scheme was provided, build one */
 165         if (!layout) {
 166
 167                 /* handle large page devices only */
 168                 if (mtd->oobsize < 64) {
 169                         printk(KERN_WARNING "must provide an oob scheme for "
 170                                "oobsize %d\n", mtd->oobsize);
 171                         goto fail;
 172                 }
 173
 174                 layout = &nbc->ecclayout;
 175                 layout->eccbytes = eccsteps*eccbytes;
 176
 177                 /* reserve 2 bytes for bad block marker */
 178                 if (layout->eccbytes+2 > mtd->oobsize) {
 179                         printk(KERN_WARNING "no suitable oob scheme available "
 180                                "for oobsize %d eccbytes %u\n", mtd->oobsize,
 181                                eccbytes);
 182                         goto fail;
 183                 }
 184                 /* put ecc bytes at oob tail */
 185                 for (i = 0; i < layout->eccbytes; i++)
 186                         layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
 187
 188                 layout->oobfree[0].offset = 2;
 189                 layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
 190
 191                 nand->ecc.layout = layout;
 192         }
 193
 194         /* sanity checks */
 195         if (8*(eccsize+eccbytes) >= (1 << m)) {
 196                 printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
 197                 goto fail;
 198         }
 199         if (layout->eccbytes != (eccsteps*eccbytes)) {
 200                 printk(KERN_WARNING "invalid ecc layout\n");
 201                 goto fail;
 202         }
 203
 204         nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
 205         nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
 206         if (!nbc->eccmask || !nbc->errloc)
 207                 goto fail;
 208         /*
 209          * compute and store the inverted ecc of an erased ecc block
 210          */
 211         erased_page = kmalloc(eccsize, GFP_KERNEL);
 212         if (!erased_page)
 213                 goto fail;
 214
 215         memset(erased_page, 0xff, eccsize);
 216         memset(nbc->eccmask, 0, eccbytes);
 217         encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
 218         kfree(erased_page);
 219
 220         for (i = 0; i < eccbytes; i++)
 221                 nbc->eccmask[i] ^= 0xff;
 222
 223         if (!eccstrength)
 224                 nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
 225
 226         return nbc;
 227 fail:
 228         nand_bch_free(nbc);
 229         return NULL;
 230 }
 231 EXPORT_SYMBOL(nand_bch_init);
 232
 233 /**
 234  * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
 235  * @nbc:        NAND BCH control structure
 236  */
 237 void nand_bch_free(struct nand_bch_control *nbc)
 238 {
 239         if (nbc) {
 240                 free_bch(nbc->bch);
 241                 kfree(nbc->errloc);
 242                 kfree(nbc->eccmask);
 243                 kfree(nbc);
 244         }
 245 }
 246 EXPORT_SYMBOL(nand_bch_free);
 247
 248 MODULE_LICENSE("GPL");
 249 MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
 250 MODULE_DESCRIPTION("NAND software BCH ECC support");