244 lines
6.9 KiB
C
244 lines
6.9 KiB
C
/*
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* This file provides ECC correction for more than 1 bit per block of data,
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* using binary BCH codes. It relies on the generic BCH library lib/bch.c.
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*
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* Copyright © 2011 Ivan Djelic <ivan.djelic@parrot.com>
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*
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* This file is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 or (at your option) any
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* later version.
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*
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* This file is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this file; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/bitops.h>
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#include <linux/mtd/mtd.h>
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#include <linux/mtd/nand.h>
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#include <linux/mtd/nand_bch.h>
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#include <linux/bch.h>
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/**
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* struct nand_bch_control - private NAND BCH control structure
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* @bch: BCH control structure
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* @ecclayout: private ecc layout for this BCH configuration
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* @errloc: error location array
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* @eccmask: XOR ecc mask, allows erased pages to be decoded as valid
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*/
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struct nand_bch_control {
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struct bch_control *bch;
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struct nand_ecclayout ecclayout;
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unsigned int *errloc;
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unsigned char *eccmask;
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};
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/**
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* nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
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* @mtd: MTD block structure
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* @buf: input buffer with raw data
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* @code: output buffer with ECC
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*/
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int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
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unsigned char *code)
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{
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const struct nand_chip *chip = mtd->priv;
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struct nand_bch_control *nbc = chip->ecc.priv;
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unsigned int i;
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memset(code, 0, chip->ecc.bytes);
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encode_bch(nbc->bch, buf, chip->ecc.size, code);
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/* apply mask so that an erased page is a valid codeword */
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for (i = 0; i < chip->ecc.bytes; i++)
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code[i] ^= nbc->eccmask[i];
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return 0;
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}
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EXPORT_SYMBOL(nand_bch_calculate_ecc);
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/**
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* nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
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* @mtd: MTD block structure
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* @buf: raw data read from the chip
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* @read_ecc: ECC from the chip
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* @calc_ecc: the ECC calculated from raw data
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*
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* Detect and correct bit errors for a data byte block
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*/
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int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
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unsigned char *read_ecc, unsigned char *calc_ecc)
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{
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const struct nand_chip *chip = mtd->priv;
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struct nand_bch_control *nbc = chip->ecc.priv;
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unsigned int *errloc = nbc->errloc;
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int i, count;
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count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
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NULL, errloc);
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if (count > 0) {
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for (i = 0; i < count; i++) {
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if (errloc[i] < (chip->ecc.size*8))
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/* error is located in data, correct it */
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buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
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/* else error in ecc, no action needed */
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pr_debug("%s: corrected bitflip %u\n", __func__,
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errloc[i]);
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}
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} else if (count < 0) {
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printk(KERN_ERR "ecc unrecoverable error\n");
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count = -1;
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}
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return count;
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}
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EXPORT_SYMBOL(nand_bch_correct_data);
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/**
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* nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
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* @mtd: MTD block structure
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* @eccsize: ecc block size in bytes
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* @eccbytes: ecc length in bytes
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* @ecclayout: output default layout
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*
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* Returns:
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* a pointer to a new NAND BCH control structure, or NULL upon failure
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*
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* Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
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* are used to compute BCH parameters m (Galois field order) and t (error
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* correction capability). @eccbytes should be equal to the number of bytes
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* required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
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*
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* Example: to configure 4 bit correction per 512 bytes, you should pass
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* @eccsize = 512 (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
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* @eccbytes = 7 (7 bytes are required to store m*t = 13*4 = 52 bits)
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*/
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struct nand_bch_control *
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nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
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struct nand_ecclayout **ecclayout)
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{
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unsigned int m, t, eccsteps, i;
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struct nand_ecclayout *layout;
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struct nand_bch_control *nbc = NULL;
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unsigned char *erased_page;
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if (!eccsize || !eccbytes) {
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printk(KERN_WARNING "ecc parameters not supplied\n");
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goto fail;
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}
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m = fls(1+8*eccsize);
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t = (eccbytes*8)/m;
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nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
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if (!nbc)
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goto fail;
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nbc->bch = init_bch(m, t, 0);
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if (!nbc->bch)
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goto fail;
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/* verify that eccbytes has the expected value */
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if (nbc->bch->ecc_bytes != eccbytes) {
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printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
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eccbytes, nbc->bch->ecc_bytes);
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goto fail;
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}
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eccsteps = mtd->writesize/eccsize;
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/* if no ecc placement scheme was provided, build one */
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if (!*ecclayout) {
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/* handle large page devices only */
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if (mtd->oobsize < 64) {
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printk(KERN_WARNING "must provide an oob scheme for "
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"oobsize %d\n", mtd->oobsize);
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goto fail;
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}
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layout = &nbc->ecclayout;
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layout->eccbytes = eccsteps*eccbytes;
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/* reserve 2 bytes for bad block marker */
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if (layout->eccbytes+2 > mtd->oobsize) {
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printk(KERN_WARNING "no suitable oob scheme available "
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"for oobsize %d eccbytes %u\n", mtd->oobsize,
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eccbytes);
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goto fail;
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}
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/* put ecc bytes at oob tail */
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for (i = 0; i < layout->eccbytes; i++)
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layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
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layout->oobfree[0].offset = 2;
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layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
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*ecclayout = layout;
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}
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/* sanity checks */
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if (8*(eccsize+eccbytes) >= (1 << m)) {
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printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
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goto fail;
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}
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if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
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printk(KERN_WARNING "invalid ecc layout\n");
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goto fail;
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}
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nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
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nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
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if (!nbc->eccmask || !nbc->errloc)
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goto fail;
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/*
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* compute and store the inverted ecc of an erased ecc block
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*/
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erased_page = kmalloc(eccsize, GFP_KERNEL);
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if (!erased_page)
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goto fail;
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memset(erased_page, 0xff, eccsize);
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memset(nbc->eccmask, 0, eccbytes);
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encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
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kfree(erased_page);
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for (i = 0; i < eccbytes; i++)
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nbc->eccmask[i] ^= 0xff;
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return nbc;
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fail:
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nand_bch_free(nbc);
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return NULL;
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}
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EXPORT_SYMBOL(nand_bch_init);
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/**
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* nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
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* @nbc: NAND BCH control structure
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*/
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void nand_bch_free(struct nand_bch_control *nbc)
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{
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if (nbc) {
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free_bch(nbc->bch);
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kfree(nbc->errloc);
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kfree(nbc->eccmask);
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kfree(nbc);
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}
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}
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EXPORT_SYMBOL(nand_bch_free);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
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MODULE_DESCRIPTION("NAND software BCH ECC support");
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