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/*
* 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 <ivan.djelic@parrot.com>
*
* 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 - private NAND BCH control structure
* @bch: BCH control structure
* @errloc: error location array
* @eccmask: XOR ecc mask, allows erased pages to be decoded as valid
*/
struct nand_bch_control {
struct bch_control *bch;
unsigned int *errloc;
unsigned char *eccmask;
};
/**
* nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
* @mtd: MTD block structure
* @buf: input buffer with raw data
* @code: output buffer with ECC
*/
int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
unsigned char *code)
{
const struct nand_chip *chip = mtd_to_nand(mtd);
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);
/**
* nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
* @mtd: MTD block structure
* @buf: raw data read from the chip
* @read_ecc: ECC from the chip
* @calc_ecc: the ECC calculated from raw data
*
* Detect and correct bit errors for a data byte block
*/
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_to_nand(mtd);
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 = -EBADMSG;
}
return count;
}
EXPORT_SYMBOL(nand_bch_correct_data);
/**
* nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
* @mtd: MTD block structure
*
* Returns:
* a pointer to a new NAND BCH control structure, or NULL upon failure
*
* Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
* are used to compute BCH parameters m (Galois field order) and t (error
* correction capability). @eccbytes should be equal to the number of bytes
* required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
*
* Example: to configure 4 bit correction per 512 bytes, you should pass
* @eccsize = 512 (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
* @eccbytes = 7 (7 bytes are required to store m*t = 13*4 = 52 bits)
*/
struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
{
struct nand_chip *nand = mtd_to_nand(mtd);
unsigned int m, t, eccsteps, i;
struct nand_bch_control *nbc = NULL;
unsigned char *erased_page;
unsigned int eccsize = nand->ecc.size;
unsigned int eccbytes = nand->ecc.bytes;
unsigned int eccstrength = nand->ecc.strength;
if (!eccbytes && eccstrength) {
eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
nand->ecc.bytes = eccbytes;
}
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;
/* Check that we have an oob layout description. */
if (!mtd->ooblayout) {
pr_warn("missing oob scheme");
goto fail;
}
/* sanity checks */
if (8*(eccsize+eccbytes) >= (1 << m)) {
printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
goto fail;
}
/*
* ecc->steps and ecc->total might be used by mtd->ooblayout->ecc(),
* which is called by mtd_ooblayout_count_eccbytes().
* Make sure they are properly initialized before calling
* mtd_ooblayout_count_eccbytes().
* FIXME: we should probably rework the sequencing in nand_scan_tail()
* to avoid setting those fields twice.
*/
nand->ecc.steps = eccsteps;
nand->ecc.total = eccsteps * eccbytes;
if (mtd_ooblayout_count_eccbytes(mtd) != (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;
if (!eccstrength)
nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
return nbc;
fail:
nand_bch_free(nbc);
return NULL;
}
EXPORT_SYMBOL(nand_bch_init);
/**
* nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
* @nbc: NAND BCH control structure
*/
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 <ivan.djelic@parrot.com>");
MODULE_DESCRIPTION("NAND software BCH ECC support");
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