nand_bch.c

Go to the documentation of this file.

/*
 * This file provides ECC correction for more than 1 bit per block of data,
 * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
 *
 * Copyright © 2011 Ivan Djelic <[email protected]>
 *
 * This file is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 or (at your option) any
 * later version.
 *
 * This file is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this file; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_bch.h>
#include <linux/bch.h>

struct nand_bch_control {
    struct bch_control   *bch;
    struct nand_ecclayout ecclayout;
    unsigned int         *errloc;
    unsigned char        *eccmask;
};

int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
               unsigned char *code)
{
    const struct nand_chip *chip = mtd->priv;
    struct nand_bch_control *nbc = chip->ecc.priv;
    unsigned int i;

    memset(code, 0, chip->ecc.bytes);
    encode_bch(nbc->bch, buf, chip->ecc.size, code);

    /* apply mask so that an erased page is a valid codeword */
    for (i = 0; i < chip->ecc.bytes; i++)
        code[i] ^= nbc->eccmask[i];

    return 0;
}
EXPORT_SYMBOL(nand_bch_calculate_ecc);

int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
              unsigned char *read_ecc, unsigned char *calc_ecc)
{
    const struct nand_chip *chip = mtd->priv;
    struct nand_bch_control *nbc = chip->ecc.priv;
    unsigned int *errloc = nbc->errloc;
    int i, count;

    count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
               NULL, errloc);
    if (count > 0) {
        for (i = 0; i < count; i++) {
            if (errloc[i] < (chip->ecc.size*8))
                /* error is located in data, correct it */
                buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
            /* else error in ecc, no action needed */

            pr_debug("%s: corrected bitflip %u\n", __func__,
                    errloc[i]);
        }
    } else if (count < 0) {
        printk(KERN_ERR "ecc unrecoverable error\n");
        count = -1;
    }
    return count;
}
EXPORT_SYMBOL(nand_bch_correct_data);

struct nand_bch_control *
nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
          struct nand_ecclayout **ecclayout)
{
    unsigned int m, t, eccsteps, i;
    struct nand_ecclayout *layout;
    struct nand_bch_control *nbc = NULL;
    unsigned char *erased_page;

    if (!eccsize || !eccbytes) {
        printk(KERN_WARNING "ecc parameters not supplied\n");
        goto fail;
    }

    m = fls(1+8*eccsize);
    t = (eccbytes*8)/m;

    nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
    if (!nbc)
        goto fail;

    nbc->bch = init_bch(m, t, 0);
    if (!nbc->bch)
        goto fail;

    /* verify that eccbytes has the expected value */
    if (nbc->bch->ecc_bytes != eccbytes) {
        printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
               eccbytes, nbc->bch->ecc_bytes);
        goto fail;
    }

    eccsteps = mtd->writesize/eccsize;

    /* if no ecc placement scheme was provided, build one */
    if (!*ecclayout) {

        /* handle large page devices only */
        if (mtd->oobsize < 64) {
            printk(KERN_WARNING "must provide an oob scheme for "
                   "oobsize %d\n", mtd->oobsize);
            goto fail;
        }

        layout = &nbc->ecclayout;
        layout->eccbytes = eccsteps*eccbytes;

        /* reserve 2 bytes for bad block marker */
        if (layout->eccbytes+2 > mtd->oobsize) {
            printk(KERN_WARNING "no suitable oob scheme available "
                   "for oobsize %d eccbytes %u\n", mtd->oobsize,
                   eccbytes);
            goto fail;
        }
        /* put ecc bytes at oob tail */
        for (i = 0; i < layout->eccbytes; i++)
            layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;

        layout->oobfree[0].offset = 2;
        layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;

        *ecclayout = layout;
    }

    /* sanity checks */
    if (8*(eccsize+eccbytes) >= (1 << m)) {
        printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
        goto fail;
    }
    if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
        printk(KERN_WARNING "invalid ecc layout\n");
        goto fail;
    }

    nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
    nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
    if (!nbc->eccmask || !nbc->errloc)
        goto fail;
    /*
     * compute and store the inverted ecc of an erased ecc block
     */
    erased_page = kmalloc(eccsize, GFP_KERNEL);
    if (!erased_page)
        goto fail;

    memset(erased_page, 0xff, eccsize);
    memset(nbc->eccmask, 0, eccbytes);
    encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
    kfree(erased_page);

    for (i = 0; i < eccbytes; i++)
        nbc->eccmask[i] ^= 0xff;

    return nbc;
fail:
    nand_bch_free(nbc);
    return NULL;
}
EXPORT_SYMBOL(nand_bch_init);

void nand_bch_free(struct nand_bch_control *nbc)
{
    if (nbc) {
        free_bch(nbc->bch);
        kfree(nbc->errloc);
        kfree(nbc->eccmask);
        kfree(nbc);
    }
}
EXPORT_SYMBOL(nand_bch_free);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Ivan Djelic <[email protected]>");
MODULE_DESCRIPTION("NAND software BCH ECC support");