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 * @ecclayout: private ecc layout for this BCH configuration
 36 * @errloc:    error location array
 37 * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
 38 */
 39struct nand_bch_control {
 40	struct bch_control   *bch;
 41	struct nand_ecclayout ecclayout;
 42	unsigned int         *errloc;
 43	unsigned char        *eccmask;
 44};
 45
 46/**
 47 * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
 48 * @mtd:	MTD block structure
 49 * @buf:	input buffer with raw data
 50 * @code:	output buffer with ECC
 51 */
 52int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
 53			   unsigned char *code)
 54{
 55	const struct nand_chip *chip = mtd->priv;
 56	struct nand_bch_control *nbc = chip->ecc.priv;
 57	unsigned int i;
 58
 59	memset(code, 0, chip->ecc.bytes);
 60	encode_bch(nbc->bch, buf, chip->ecc.size, code);
 61
 62	/* apply mask so that an erased page is a valid codeword */
 63	for (i = 0; i < chip->ecc.bytes; i++)
 64		code[i] ^= nbc->eccmask[i];
 65
 66	return 0;
 67}
 68EXPORT_SYMBOL(nand_bch_calculate_ecc);
 69
 70/**
 71 * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
 72 * @mtd:	MTD block structure
 73 * @buf:	raw data read from the chip
 74 * @read_ecc:	ECC from the chip
 75 * @calc_ecc:	the ECC calculated from raw data
 76 *
 77 * Detect and correct bit errors for a data byte block
 78 */
 79int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
 80			  unsigned char *read_ecc, unsigned char *calc_ecc)
 81{
 82	const struct nand_chip *chip = mtd->priv;
 83	struct nand_bch_control *nbc = chip->ecc.priv;
 84	unsigned int *errloc = nbc->errloc;
 85	int i, count;
 86
 87	count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
 88			   NULL, errloc);
 89	if (count > 0) {
 90		for (i = 0; i < count; i++) {
 91			if (errloc[i] < (chip->ecc.size*8))
 92				/* error is located in data, correct it */
 93				buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
 94			/* else error in ecc, no action needed */
 95
 96			pr_debug("%s: corrected bitflip %u\n", __func__,
 97					errloc[i]);
 98		}
 99	} else if (count < 0) {
100		printk(KERN_ERR "ecc unrecoverable error\n");
101		count = -1;
102	}
103	return count;
104}
105EXPORT_SYMBOL(nand_bch_correct_data);
106
107/**
108 * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
109 * @mtd:	MTD block structure
110 * @eccsize:	ecc block size in bytes
111 * @eccbytes:	ecc length in bytes
112 * @ecclayout:	output default layout
113 *
114 * Returns:
115 *  a pointer to a new NAND BCH control structure, or NULL upon failure
116 *
117 * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
118 * are used to compute BCH parameters m (Galois field order) and t (error
119 * correction capability). @eccbytes should be equal to the number of bytes
120 * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
121 *
122 * Example: to configure 4 bit correction per 512 bytes, you should pass
123 * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
124 * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
125 */
126struct nand_bch_control *
127nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
128	      struct nand_ecclayout **ecclayout)
129{
130	unsigned int m, t, eccsteps, i;
131	struct nand_ecclayout *layout;
132	struct nand_bch_control *nbc = NULL;
133	unsigned char *erased_page;
134
135	if (!eccsize || !eccbytes) {
136		printk(KERN_WARNING "ecc parameters not supplied\n");
137		goto fail;
138	}
139
140	m = fls(1+8*eccsize);
141	t = (eccbytes*8)/m;
142
143	nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
144	if (!nbc)
145		goto fail;
146
147	nbc->bch = init_bch(m, t, 0);
148	if (!nbc->bch)
149		goto fail;
150
151	/* verify that eccbytes has the expected value */
152	if (nbc->bch->ecc_bytes != eccbytes) {
153		printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
154		       eccbytes, nbc->bch->ecc_bytes);
155		goto fail;
156	}
157
158	eccsteps = mtd->writesize/eccsize;
159
160	/* if no ecc placement scheme was provided, build one */
161	if (!*ecclayout) {
162
163		/* handle large page devices only */
164		if (mtd->oobsize < 64) {
165			printk(KERN_WARNING "must provide an oob scheme for "
166			       "oobsize %d\n", mtd->oobsize);
167			goto fail;
168		}
169
170		layout = &nbc->ecclayout;
171		layout->eccbytes = eccsteps*eccbytes;
172
173		/* reserve 2 bytes for bad block marker */
174		if (layout->eccbytes+2 > mtd->oobsize) {
175			printk(KERN_WARNING "no suitable oob scheme available "
176			       "for oobsize %d eccbytes %u\n", mtd->oobsize,
177			       eccbytes);
178			goto fail;
179		}
180		/* put ecc bytes at oob tail */
181		for (i = 0; i < layout->eccbytes; i++)
182			layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
183
184		layout->oobfree[0].offset = 2;
185		layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
186
187		*ecclayout = layout;
188	}
189
190	/* sanity checks */
191	if (8*(eccsize+eccbytes) >= (1 << m)) {
192		printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
193		goto fail;
194	}
195	if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
196		printk(KERN_WARNING "invalid ecc layout\n");
197		goto fail;
198	}
199
200	nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
201	nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
202	if (!nbc->eccmask || !nbc->errloc)
203		goto fail;
204	/*
205	 * compute and store the inverted ecc of an erased ecc block
206	 */
207	erased_page = kmalloc(eccsize, GFP_KERNEL);
208	if (!erased_page)
209		goto fail;
210
211	memset(erased_page, 0xff, eccsize);
212	memset(nbc->eccmask, 0, eccbytes);
213	encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
214	kfree(erased_page);
215
216	for (i = 0; i < eccbytes; i++)
217		nbc->eccmask[i] ^= 0xff;
218
219	return nbc;
220fail:
221	nand_bch_free(nbc);
222	return NULL;
223}
224EXPORT_SYMBOL(nand_bch_init);
225
226/**
227 * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
228 * @nbc:	NAND BCH control structure
229 */
230void nand_bch_free(struct nand_bch_control *nbc)
231{
232	if (nbc) {
233		free_bch(nbc->bch);
234		kfree(nbc->errloc);
235		kfree(nbc->eccmask);
236		kfree(nbc);
237	}
238}
239EXPORT_SYMBOL(nand_bch_free);
240
241MODULE_LICENSE("GPL");
242MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
243MODULE_DESCRIPTION("NAND software BCH ECC support");