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 * This file is free software; you can redistribute it and/or modify it
  8 * under the terms of the GNU General Public License as published by the
  9 * Free Software Foundation; either version 2 or (at your option) any
 10 * later version.
 11 *
 12 * This file is distributed in the hope that it will be useful, but WITHOUT
 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 14 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 15 * for more details.
 16 *
 17 * You should have received a copy of the GNU General Public License along
 18 * with this file; if not, write to the Free Software Foundation, Inc.,
 19 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 20 */
 21
 22#include <linux/types.h>
 23#include <linux/kernel.h>
 24#include <linux/module.h>
 25#include <linux/slab.h>
 26#include <linux/bitops.h>
 27#include <linux/mtd/mtd.h>
 28#include <linux/mtd/nand.h>
 29#include <linux/mtd/nand_bch.h>
 30#include <linux/bch.h>
 31
 32/**
 33 * struct nand_bch_control - private NAND BCH control structure
 34 * @bch:       BCH control structure
 35 * @errloc:    error location array
 36 * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
 37 */
 38struct nand_bch_control {
 39	struct bch_control   *bch;
 40	unsigned int         *errloc;
 41	unsigned char        *eccmask;
 42};
 43
 44/**
 45 * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
 46 * @mtd:	MTD block structure
 47 * @buf:	input buffer with raw data
 48 * @code:	output buffer with ECC
 49 */
 50int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
 51			   unsigned char *code)
 52{
 53	const struct nand_chip *chip = mtd_to_nand(mtd);
 54	struct nand_bch_control *nbc = chip->ecc.priv;
 55	unsigned int i;
 56
 57	memset(code, 0, chip->ecc.bytes);
 58	encode_bch(nbc->bch, buf, chip->ecc.size, code);
 59
 60	/* apply mask so that an erased page is a valid codeword */
 61	for (i = 0; i < chip->ecc.bytes; i++)
 62		code[i] ^= nbc->eccmask[i];
 63
 64	return 0;
 65}
 66EXPORT_SYMBOL(nand_bch_calculate_ecc);
 67
 68/**
 69 * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
 70 * @mtd:	MTD block structure
 71 * @buf:	raw data read from the chip
 72 * @read_ecc:	ECC from the chip
 73 * @calc_ecc:	the ECC calculated from raw data
 74 *
 75 * Detect and correct bit errors for a data byte block
 76 */
 77int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
 78			  unsigned char *read_ecc, unsigned char *calc_ecc)
 79{
 80	const struct nand_chip *chip = mtd_to_nand(mtd);
 81	struct nand_bch_control *nbc = chip->ecc.priv;
 82	unsigned int *errloc = nbc->errloc;
 83	int i, count;
 84
 85	count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
 86			   NULL, errloc);
 87	if (count > 0) {
 88		for (i = 0; i < count; i++) {
 89			if (errloc[i] < (chip->ecc.size*8))
 90				/* error is located in data, correct it */
 91				buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
 92			/* else error in ecc, no action needed */
 93
 94			pr_debug("%s: corrected bitflip %u\n", __func__,
 95					errloc[i]);
 96		}
 97	} else if (count < 0) {
 98		printk(KERN_ERR "ecc unrecoverable error\n");
 99		count = -EBADMSG;
100	}
101	return count;
102}
103EXPORT_SYMBOL(nand_bch_correct_data);
104
105/**
106 * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
107 * @mtd:	MTD block structure
108 *
109 * Returns:
110 *  a pointer to a new NAND BCH control structure, or NULL upon failure
111 *
112 * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
113 * are used to compute BCH parameters m (Galois field order) and t (error
114 * correction capability). @eccbytes should be equal to the number of bytes
115 * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
116 *
117 * Example: to configure 4 bit correction per 512 bytes, you should pass
118 * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
119 * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
120 */
121struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
122{
123	struct nand_chip *nand = mtd_to_nand(mtd);
124	unsigned int m, t, eccsteps, i;
125	struct nand_bch_control *nbc = NULL;
126	unsigned char *erased_page;
127	unsigned int eccsize = nand->ecc.size;
128	unsigned int eccbytes = nand->ecc.bytes;
129	unsigned int eccstrength = nand->ecc.strength;
130
131	if (!eccbytes && eccstrength) {
132		eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
133		nand->ecc.bytes = eccbytes;
134	}
135
136	if (!eccsize || !eccbytes) {
137		printk(KERN_WARNING "ecc parameters not supplied\n");
138		goto fail;
139	}
140
141	m = fls(1+8*eccsize);
142	t = (eccbytes*8)/m;
143
144	nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
145	if (!nbc)
146		goto fail;
147
148	nbc->bch = init_bch(m, t, 0);
149	if (!nbc->bch)
150		goto fail;
151
152	/* verify that eccbytes has the expected value */
153	if (nbc->bch->ecc_bytes != eccbytes) {
154		printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
155		       eccbytes, nbc->bch->ecc_bytes);
156		goto fail;
157	}
158
159	eccsteps = mtd->writesize/eccsize;
160
161	/* Check that we have an oob layout description. */
162	if (!mtd->ooblayout) {
163		pr_warn("missing oob scheme");
164		goto fail;
165	}
166
167	/* sanity checks */
168	if (8*(eccsize+eccbytes) >= (1 << m)) {
169		printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
170		goto fail;
171	}
172
173	/*
174	 * ecc->steps and ecc->total might be used by mtd->ooblayout->ecc(),
175	 * which is called by mtd_ooblayout_count_eccbytes().
176	 * Make sure they are properly initialized before calling
177	 * mtd_ooblayout_count_eccbytes().
178	 * FIXME: we should probably rework the sequencing in nand_scan_tail()
179	 * to avoid setting those fields twice.
180	 */
181	nand->ecc.steps = eccsteps;
182	nand->ecc.total = eccsteps * eccbytes;
183	if (mtd_ooblayout_count_eccbytes(mtd) != (eccsteps*eccbytes)) {
184		printk(KERN_WARNING "invalid ecc layout\n");
185		goto fail;
186	}
187
188	nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
189	nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
190	if (!nbc->eccmask || !nbc->errloc)
191		goto fail;
192	/*
193	 * compute and store the inverted ecc of an erased ecc block
194	 */
195	erased_page = kmalloc(eccsize, GFP_KERNEL);
196	if (!erased_page)
197		goto fail;
198
199	memset(erased_page, 0xff, eccsize);
200	memset(nbc->eccmask, 0, eccbytes);
201	encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
202	kfree(erased_page);
203
204	for (i = 0; i < eccbytes; i++)
205		nbc->eccmask[i] ^= 0xff;
206
207	if (!eccstrength)
208		nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
209
210	return nbc;
211fail:
212	nand_bch_free(nbc);
213	return NULL;
214}
215EXPORT_SYMBOL(nand_bch_init);
216
217/**
218 * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
219 * @nbc:	NAND BCH control structure
220 */
221void nand_bch_free(struct nand_bch_control *nbc)
222{
223	if (nbc) {
224		free_bch(nbc->bch);
225		kfree(nbc->errloc);
226		kfree(nbc->eccmask);
227		kfree(nbc);
228	}
229}
230EXPORT_SYMBOL(nand_bch_free);
231
232MODULE_LICENSE("GPL");
233MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
234MODULE_DESCRIPTION("NAND software BCH ECC support");