/*
 * 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
 * @ecclayout: private ecc layout for this BCH configuration
 * @errloc:    error location array
 * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
 */
struct nand_bch_control {
        struct bch_control   *bch;
        struct nand_ecclayout ecclayout;
        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->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);

/**
 * 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->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);

/**
 * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
 * @mtd:        MTD block structure
 * @eccsize:    ecc block size in bytes
 * @eccbytes:   ecc length in bytes
 * @ecclayout:  output default layout
 *
 * 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, 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);

/**
 * 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");