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   * SPDX-License-Identifier:    GPL-2.0+
   8  */
   9
  10 #include <common.h>
  11 /*#include <asm/io.h>*/
  12 #include <linux/types.h>
  13
  14 #include <linux/bitops.h>
  15 #include <linux/mtd/mtd.h>
  16 #include <linux/mtd/nand.h>
  17 #include <linux/mtd/nand_bch.h>
  18 #include <linux/bch.h>
  19 #include <malloc.h>
  20
  21 /**
  22  * struct nand_bch_control - private NAND BCH control structure
  23  * @bch:       BCH control structure
  24  * @ecclayout: private ecc layout for this BCH configuration
  25  * @errloc:    error location array
  26  * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
  27  */
  28 struct nand_bch_control {
  29         struct bch_control   *bch;
  30         struct nand_ecclayout ecclayout;
  31         unsigned int         *errloc;
  32         unsigned char        *eccmask;
  33 };
  34
  35 /**
  36  * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
  37  * @mtd:        MTD block structure
  38  * @buf:        input buffer with raw data
  39  * @code:       output buffer with ECC
  40  */
  41 int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
  42                            unsigned char *code)
  43 {
  44         const struct nand_chip *chip = mtd->priv;
  45         struct nand_bch_control *nbc = chip->ecc.priv;
  46         unsigned int i;
  47
  48         memset(code, 0, chip->ecc.bytes);
  49         encode_bch(nbc->bch, buf, chip->ecc.size, code);
  50
  51         /* apply mask so that an erased page is a valid codeword */
  52         for (i = 0; i < chip->ecc.bytes; i++)
  53                 code[i] ^= nbc->eccmask[i];
  54
  55         return 0;
  56 }
  57
  58 /**
  59  * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
  60  * @mtd:        MTD block structure
  61  * @buf:        raw data read from the chip
  62  * @read_ecc:   ECC from the chip
  63  * @calc_ecc:   the ECC calculated from raw data
  64  *
  65  * Detect and correct bit errors for a data byte block
  66  */
  67 int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
  68                           unsigned char *read_ecc, unsigned char *calc_ecc)
  69 {
  70         const struct nand_chip *chip = mtd->priv;
  71         struct nand_bch_control *nbc = chip->ecc.priv;
  72         unsigned int *errloc = nbc->errloc;
  73         int i, count;
  74
  75         count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
  76                            NULL, errloc);
  77         if (count > 0) {
  78                 for (i = 0; i < count; i++) {
  79                         if (errloc[i] < (chip->ecc.size*8))
  80                                 /* error is located in data, correct it */
  81                                 buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
  82                         /* else error in ecc, no action needed */
  83
  84                         MTDDEBUG(MTD_DEBUG_LEVEL0, "%s: corrected bitflip %u\n",
  85                               __func__, errloc[i]);
  86                 }
  87         } else if (count < 0) {
  88                 printk(KERN_ERR "ecc unrecoverable error\n");
  89                 count = -1;
  90         }
  91         return count;
  92 }
  93
  94 /**
  95  * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
  96  * @mtd:        MTD block structure
  97  * @eccsize:    ecc block size in bytes
  98  * @eccbytes:   ecc length in bytes
  99  * @ecclayout:  output default layout
 100  *
 101  * Returns:
 102  *  a pointer to a new NAND BCH control structure, or NULL upon failure
 103  *
 104  * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
 105  * are used to compute BCH parameters m (Galois field order) and t (error
 106  * correction capability). @eccbytes should be equal to the number of bytes
 107  * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
 108  *
 109  * Example: to configure 4 bit correction per 512 bytes, you should pass
 110  * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
 111  * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
 112  */
 113 struct nand_bch_control *
 114 nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
 115               struct nand_ecclayout **ecclayout)
 116 {
 117         unsigned int m, t, eccsteps, i;
 118         struct nand_ecclayout *layout;
 119         struct nand_bch_control *nbc = NULL;
 120         unsigned char *erased_page;
 121
 122         if (!eccsize || !eccbytes) {
 123                 printk(KERN_WARNING "ecc parameters not supplied\n");
 124                 goto fail;
 125         }
 126
 127         m = fls(1+8*eccsize);
 128         t = (eccbytes*8)/m;
 129
 130         nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
 131         if (!nbc)
 132                 goto fail;
 133
 134         nbc->bch = init_bch(m, t, 0);
 135         if (!nbc->bch)
 136                 goto fail;
 137
 138         /* verify that eccbytes has the expected value */
 139         if (nbc->bch->ecc_bytes != eccbytes) {
 140                 printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
 141                        eccbytes, nbc->bch->ecc_bytes);
 142                 goto fail;
 143         }
 144
 145         eccsteps = mtd->writesize/eccsize;
 146
 147         /* if no ecc placement scheme was provided, build one */
 148         if (!*ecclayout) {
 149
 150                 /* handle large page devices only */
 151                 if (mtd->oobsize < 64) {
 152                         printk(KERN_WARNING "must provide an oob scheme for "
 153                                "oobsize %d\n", mtd->oobsize);
 154                         goto fail;
 155                 }
 156
 157                 layout = &nbc->ecclayout;
 158                 layout->eccbytes = eccsteps*eccbytes;
 159
 160                 /* reserve 2 bytes for bad block marker */
 161                 if (layout->eccbytes+2 > mtd->oobsize) {
 162                         printk(KERN_WARNING "no suitable oob scheme available "
 163                                "for oobsize %d eccbytes %u\n", mtd->oobsize,
 164                                eccbytes);
 165                         goto fail;
 166                 }
 167                 /* put ecc bytes at oob tail */
 168                 for (i = 0; i < layout->eccbytes; i++)
 169                         layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
 170
 171                 layout->oobfree[0].offset = 2;
 172                 layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
 173
 174                 *ecclayout = layout;
 175         }
 176
 177         /* sanity checks */
 178         if (8*(eccsize+eccbytes) >= (1 << m)) {
 179                 printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
 180                 goto fail;
 181         }
 182         if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
 183                 printk(KERN_WARNING "invalid ecc layout\n");
 184                 goto fail;
 185         }
 186
 187         nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
 188         nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
 189         if (!nbc->eccmask || !nbc->errloc)
 190                 goto fail;
 191         /*
 192          * compute and store the inverted ecc of an erased ecc block
 193          */
 194         erased_page = kmalloc(eccsize, GFP_KERNEL);
 195         if (!erased_page)
 196                 goto fail;
 197
 198         memset(erased_page, 0xff, eccsize);
 199         memset(nbc->eccmask, 0, eccbytes);
 200         encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
 201         kfree(erased_page);
 202
 203         for (i = 0; i < eccbytes; i++)
 204                 nbc->eccmask[i] ^= 0xff;
 205
 206         return nbc;
 207 fail:
 208         nand_bch_free(nbc);
 209         return NULL;
 210 }
 211
 212 /**
 213  * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
 214  * @nbc:        NAND BCH control structure
 215  */
 216 void nand_bch_free(struct nand_bch_control *nbc)
 217 {
 218         if (nbc) {
 219                 free_bch(nbc->bch);
 220                 kfree(nbc->errloc);
 221                 kfree(nbc->eccmask);
 222                 kfree(nbc);
 223         }
 224 }