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->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  */
  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                         DEBUG(MTD_DEBUG_LEVEL0, "%s: corrected bitflip %u\n",
  97                               __func__, 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 *
 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  */
 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");