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  * @errloc:    error location array
  36  * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
  37  */
  38 struct nand_bch_control {
  39         struct bch_control   *bch;
  40         unsigned int         *errloc;
  41         unsigned char        *eccmask;
  42 };
  43
  44 /**
  45  * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
  46  * @mtd:        MTD block structure
  47  * @buf:        input buffer with raw data
  48  * @code:       output buffer with ECC
  49  */
  50 int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
  51                            unsigned char *code)
  52 {
  53         const struct nand_chip *chip = mtd_to_nand(mtd);
  54         struct nand_bch_control *nbc = chip->ecc.priv;
  55         unsigned int i;
  56
  57         memset(code, 0, chip->ecc.bytes);
  58         encode_bch(nbc->bch, buf, chip->ecc.size, code);
  59
  60         /* apply mask so that an erased page is a valid codeword */
  61         for (i = 0; i < chip->ecc.bytes; i++)
  62                 code[i] ^= nbc->eccmask[i];
  63
  64         return 0;
  65 }
  66 EXPORT_SYMBOL(nand_bch_calculate_ecc);
  67
  68 /**
  69  * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
  70  * @mtd:        MTD block structure
  71  * @buf:        raw data read from the chip
  72  * @read_ecc:   ECC from the chip
  73  * @calc_ecc:   the ECC calculated from raw data
  74  *
  75  * Detect and correct bit errors for a data byte block
  76  */
  77 int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
  78                           unsigned char *read_ecc, unsigned char *calc_ecc)
  79 {
  80         const struct nand_chip *chip = mtd_to_nand(mtd);
  81         struct nand_bch_control *nbc = chip->ecc.priv;
  82         unsigned int *errloc = nbc->errloc;
  83         int i, count;
  84
  85         count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
  86                            NULL, errloc);
  87         if (count > 0) {
  88                 for (i = 0; i < count; i++) {
  89                         if (errloc[i] < (chip->ecc.size*8))
  90                                 /* error is located in data, correct it */
  91                                 buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
  92                         /* else error in ecc, no action needed */
  93
  94                         pr_debug("%s: corrected bitflip %u\n", __func__,
  95                                         errloc[i]);
  96                 }
  97         } else if (count < 0) {
  98                 printk(KERN_ERR "ecc unrecoverable error\n");
  99                 count = -EBADMSG;
 100         }
 101         return count;
 102 }
 103 EXPORT_SYMBOL(nand_bch_correct_data);
 104
 105 /**
 106  * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
 107  * @mtd:        MTD block structure
 108  *
 109  * Returns:
 110  *  a pointer to a new NAND BCH control structure, or NULL upon failure
 111  *
 112  * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
 113  * are used to compute BCH parameters m (Galois field order) and t (error
 114  * correction capability). @eccbytes should be equal to the number of bytes
 115  * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
 116  *
 117  * Example: to configure 4 bit correction per 512 bytes, you should pass
 118  * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
 119  * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
 120  */
 121 struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
 122 {
 123         struct nand_chip *nand = mtd_to_nand(mtd);
 124         unsigned int m, t, eccsteps, i;
 125         struct nand_bch_control *nbc = NULL;
 126         unsigned char *erased_page;
 127         unsigned int eccsize = nand->ecc.size;
 128         unsigned int eccbytes = nand->ecc.bytes;
 129         unsigned int eccstrength = nand->ecc.strength;
 130
 131         if (!eccbytes && eccstrength) {
 132                 eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
 133                 nand->ecc.bytes = eccbytes;
 134         }
 135
 136         if (!eccsize || !eccbytes) {
 137                 printk(KERN_WARNING "ecc parameters not supplied\n");
 138                 goto fail;
 139         }
 140
 141         m = fls(1+8*eccsize);
 142         t = (eccbytes*8)/m;
 143
 144         nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
 145         if (!nbc)
 146                 goto fail;
 147
 148         nbc->bch = init_bch(m, t, 0);
 149         if (!nbc->bch)
 150                 goto fail;
 151
 152         /* verify that eccbytes has the expected value */
 153         if (nbc->bch->ecc_bytes != eccbytes) {
 154                 printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
 155                        eccbytes, nbc->bch->ecc_bytes);
 156                 goto fail;
 157         }
 158
 159         eccsteps = mtd->writesize/eccsize;
 160
 161         /* Check that we have an oob layout description. */
 162         if (!mtd->ooblayout) {
 163                 pr_warn("missing oob scheme");
 164                 goto fail;
 165         }
 166
 167         /* sanity checks */
 168         if (8*(eccsize+eccbytes) >= (1 << m)) {
 169                 printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
 170                 goto fail;
 171         }
 172
 173         /*
 174          * ecc->steps and ecc->total might be used by mtd->ooblayout->ecc(),
 175          * which is called by mtd_ooblayout_count_eccbytes().
 176          * Make sure they are properly initialized before calling
 177          * mtd_ooblayout_count_eccbytes().
 178          * FIXME: we should probably rework the sequencing in nand_scan_tail()
 179          * to avoid setting those fields twice.
 180          */
 181         nand->ecc.steps = eccsteps;
 182         nand->ecc.total = eccsteps * eccbytes;
 183         if (mtd_ooblayout_count_eccbytes(mtd) != (eccsteps*eccbytes)) {
 184                 printk(KERN_WARNING "invalid ecc layout\n");
 185                 goto fail;
 186         }
 187
 188         nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
 189         nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
 190         if (!nbc->eccmask || !nbc->errloc)
 191                 goto fail;
 192         /*
 193          * compute and store the inverted ecc of an erased ecc block
 194          */
 195         erased_page = kmalloc(eccsize, GFP_KERNEL);
 196         if (!erased_page)
 197                 goto fail;
 198
 199         memset(erased_page, 0xff, eccsize);
 200         memset(nbc->eccmask, 0, eccbytes);
 201         encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
 202         kfree(erased_page);
 203
 204         for (i = 0; i < eccbytes; i++)
 205                 nbc->eccmask[i] ^= 0xff;
 206
 207         if (!eccstrength)
 208                 nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
 209
 210         return nbc;
 211 fail:
 212         nand_bch_free(nbc);
 213         return NULL;
 214 }
 215 EXPORT_SYMBOL(nand_bch_init);
 216
 217 /**
 218  * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
 219  * @nbc:        NAND BCH control structure
 220  */
 221 void nand_bch_free(struct nand_bch_control *nbc)
 222 {
 223         if (nbc) {
 224                 free_bch(nbc->bch);
 225                 kfree(nbc->errloc);
 226                 kfree(nbc->eccmask);
 227                 kfree(nbc);
 228         }
 229 }
 230 EXPORT_SYMBOL(nand_bch_free);
 231
 232 MODULE_LICENSE("GPL");
 233 MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
 234 MODULE_DESCRIPTION("NAND software BCH ECC support");