root/drivers/mtd/nand/raw/nand_bch.c

DEFINITIONS

1. nand_bch_calculate_ecc
2. nand_bch_correct_data
3. nand_bch_init
4. nand_bch_free

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * This file provides ECC correction for more than 1 bit per block of data,
   4  * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
   5  *
   6  * Copyright © 2011 Ivan Djelic <ivan.djelic@parrot.com>
   7  */
   8 
   9 #include <linux/types.h>
  10 #include <linux/kernel.h>
  11 #include <linux/module.h>
  12 #include <linux/slab.h>
  13 #include <linux/bitops.h>
  14 #include <linux/mtd/mtd.h>
  15 #include <linux/mtd/rawnand.h>
  16 #include <linux/mtd/nand_bch.h>
  17 #include <linux/bch.h>
  18 
  19 /**
  20  * struct nand_bch_control - private NAND BCH control structure
  21  * @bch:       BCH control structure
  22  * @errloc:    error location array
  23  * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
  24  */
  25 struct nand_bch_control {
  26         struct bch_control   *bch;
  27         unsigned int         *errloc;
  28         unsigned char        *eccmask;
  29 };
  30 
  31 /**
  32  * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
  33  * @chip:       NAND chip object
  34  * @buf:        input buffer with raw data
  35  * @code:       output buffer with ECC
  36  */
  37 int nand_bch_calculate_ecc(struct nand_chip *chip, const unsigned char *buf,
  38                            unsigned char *code)
  39 {
  40         struct nand_bch_control *nbc = chip->ecc.priv;
  41         unsigned int i;
  42 
  43         memset(code, 0, chip->ecc.bytes);
  44         encode_bch(nbc->bch, buf, chip->ecc.size, code);
  45 
  46         /* apply mask so that an erased page is a valid codeword */
  47         for (i = 0; i < chip->ecc.bytes; i++)
  48                 code[i] ^= nbc->eccmask[i];
  49 
  50         return 0;
  51 }
  52 EXPORT_SYMBOL(nand_bch_calculate_ecc);
  53 
  54 /**
  55  * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
  56  * @chip:       NAND chip object
  57  * @buf:        raw data read from the chip
  58  * @read_ecc:   ECC from the chip
  59  * @calc_ecc:   the ECC calculated from raw data
  60  *
  61  * Detect and correct bit errors for a data byte block
  62  */
  63 int nand_bch_correct_data(struct nand_chip *chip, unsigned char *buf,
  64                           unsigned char *read_ecc, unsigned char *calc_ecc)
  65 {
  66         struct nand_bch_control *nbc = chip->ecc.priv;
  67         unsigned int *errloc = nbc->errloc;
  68         int i, count;
  69 
  70         count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
  71                            NULL, errloc);
  72         if (count > 0) {
  73                 for (i = 0; i < count; i++) {
  74                         if (errloc[i] < (chip->ecc.size*8))
  75                                 /* error is located in data, correct it */
  76                                 buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
  77                         /* else error in ecc, no action needed */
  78 
  79                         pr_debug("%s: corrected bitflip %u\n", __func__,
  80                                         errloc[i]);
  81                 }
  82         } else if (count < 0) {
  83                 pr_err("ecc unrecoverable error\n");
  84                 count = -EBADMSG;
  85         }
  86         return count;
  87 }
  88 EXPORT_SYMBOL(nand_bch_correct_data);
  89 
  90 /**
  91  * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
  92  * @mtd:        MTD block structure
  93  *
  94  * Returns:
  95  *  a pointer to a new NAND BCH control structure, or NULL upon failure
  96  *
  97  * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
  98  * are used to compute BCH parameters m (Galois field order) and t (error
  99  * correction capability). @eccbytes should be equal to the number of bytes
 100  * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
 101  *
 102  * Example: to configure 4 bit correction per 512 bytes, you should pass
 103  * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
 104  * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
 105  */
 106 struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
 107 {
 108         struct nand_chip *nand = mtd_to_nand(mtd);
 109         unsigned int m, t, eccsteps, i;
 110         struct nand_bch_control *nbc = NULL;
 111         unsigned char *erased_page;
 112         unsigned int eccsize = nand->ecc.size;
 113         unsigned int eccbytes = nand->ecc.bytes;
 114         unsigned int eccstrength = nand->ecc.strength;
 115 
 116         if (!eccbytes && eccstrength) {
 117                 eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
 118                 nand->ecc.bytes = eccbytes;
 119         }
 120 
 121         if (!eccsize || !eccbytes) {
 122                 pr_warn("ecc parameters not supplied\n");
 123                 goto fail;
 124         }
 125 
 126         m = fls(1+8*eccsize);
 127         t = (eccbytes*8)/m;
 128 
 129         nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
 130         if (!nbc)
 131                 goto fail;
 132 
 133         nbc->bch = init_bch(m, t, 0);
 134         if (!nbc->bch)
 135                 goto fail;
 136 
 137         /* verify that eccbytes has the expected value */
 138         if (nbc->bch->ecc_bytes != eccbytes) {
 139                 pr_warn("invalid eccbytes %u, should be %u\n",
 140                         eccbytes, nbc->bch->ecc_bytes);
 141                 goto fail;
 142         }
 143 
 144         eccsteps = mtd->writesize/eccsize;
 145 
 146         /* Check that we have an oob layout description. */
 147         if (!mtd->ooblayout) {
 148                 pr_warn("missing oob scheme");
 149                 goto fail;
 150         }
 151 
 152         /* sanity checks */
 153         if (8*(eccsize+eccbytes) >= (1 << m)) {
 154                 pr_warn("eccsize %u is too large\n", eccsize);
 155                 goto fail;
 156         }
 157 
 158         /*
 159          * ecc->steps and ecc->total might be used by mtd->ooblayout->ecc(),
 160          * which is called by mtd_ooblayout_count_eccbytes().
 161          * Make sure they are properly initialized before calling
 162          * mtd_ooblayout_count_eccbytes().
 163          * FIXME: we should probably rework the sequencing in nand_scan_tail()
 164          * to avoid setting those fields twice.
 165          */
 166         nand->ecc.steps = eccsteps;
 167         nand->ecc.total = eccsteps * eccbytes;
 168         if (mtd_ooblayout_count_eccbytes(mtd) != (eccsteps*eccbytes)) {
 169                 pr_warn("invalid ecc layout\n");
 170                 goto fail;
 171         }
 172 
 173         nbc->eccmask = kzalloc(eccbytes, GFP_KERNEL);
 174         nbc->errloc = kmalloc_array(t, sizeof(*nbc->errloc), GFP_KERNEL);
 175         if (!nbc->eccmask || !nbc->errloc)
 176                 goto fail;
 177         /*
 178          * compute and store the inverted ecc of an erased ecc block
 179          */
 180         erased_page = kmalloc(eccsize, GFP_KERNEL);
 181         if (!erased_page)
 182                 goto fail;
 183 
 184         memset(erased_page, 0xff, eccsize);
 185         encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
 186         kfree(erased_page);
 187 
 188         for (i = 0; i < eccbytes; i++)
 189                 nbc->eccmask[i] ^= 0xff;
 190 
 191         if (!eccstrength)
 192                 nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
 193 
 194         return nbc;
 195 fail:
 196         nand_bch_free(nbc);
 197         return NULL;
 198 }
 199 EXPORT_SYMBOL(nand_bch_init);
 200 
 201 /**
 202  * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
 203  * @nbc:        NAND BCH control structure
 204  */
 205 void nand_bch_free(struct nand_bch_control *nbc)
 206 {
 207         if (nbc) {
 208                 free_bch(nbc->bch);
 209                 kfree(nbc->errloc);
 210                 kfree(nbc->eccmask);
 211                 kfree(nbc);
 212         }
 213 }
 214 EXPORT_SYMBOL(nand_bch_free);
 215 
 216 MODULE_LICENSE("GPL");
 217 MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
 218 MODULE_DESCRIPTION("NAND software BCH ECC support");