1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * This file provides ECC correction for more than 1 bit per block of data,
4 * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
5 *
6 * Copyright © 2011 Ivan Djelic <ivan.djelic@parrot.com>
7 */
8
9#include <linux/types.h>
10#include <linux/kernel.h>
11#include <linux/module.h>
12#include <linux/slab.h>
13#include <linux/bitops.h>
14#include <linux/mtd/mtd.h>
15#include <linux/mtd/rawnand.h>
16#include <linux/mtd/nand_bch.h>
17#include <linux/bch.h>
18
19/**
20 * struct nand_bch_control - private NAND BCH control structure
21 * @bch:       BCH control structure
22 * @errloc:    error location array
23 * @eccmask:   XOR ecc mask, allows erased pages to be decoded as valid
24 */
25struct nand_bch_control {
26	struct bch_control   *bch;
27	unsigned int         *errloc;
28	unsigned char        *eccmask;
29};
30
31/**
32 * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
33 * @chip:	NAND chip object
34 * @buf:	input buffer with raw data
35 * @code:	output buffer with ECC
36 */
37int nand_bch_calculate_ecc(struct nand_chip *chip, const unsigned char *buf,
38			   unsigned char *code)
39{
40	struct nand_bch_control *nbc = chip->ecc.priv;
41	unsigned int i;
42
43	memset(code, 0, chip->ecc.bytes);
44	bch_encode(nbc->bch, buf, chip->ecc.size, code);
45
46	/* apply mask so that an erased page is a valid codeword */
47	for (i = 0; i < chip->ecc.bytes; i++)
48		code[i] ^= nbc->eccmask[i];
49
50	return 0;
51}
52EXPORT_SYMBOL(nand_bch_calculate_ecc);
53
54/**
55 * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
56 * @chip:	NAND chip object
57 * @buf:	raw data read from the chip
58 * @read_ecc:	ECC from the chip
59 * @calc_ecc:	the ECC calculated from raw data
60 *
61 * Detect and correct bit errors for a data byte block
62 */
63int nand_bch_correct_data(struct nand_chip *chip, unsigned char *buf,
64			  unsigned char *read_ecc, unsigned char *calc_ecc)
65{
66	struct nand_bch_control *nbc = chip->ecc.priv;
67	unsigned int *errloc = nbc->errloc;
68	int i, count;
69
70	count = bch_decode(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
71			   NULL, errloc);
72	if (count > 0) {
73		for (i = 0; i < count; i++) {
74			if (errloc[i] < (chip->ecc.size*8))
75				/* error is located in data, correct it */
76				buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
77			/* else error in ecc, no action needed */
78
79			pr_debug("%s: corrected bitflip %u\n", __func__,
80					errloc[i]);
81		}
82	} else if (count < 0) {
83		pr_err("ecc unrecoverable error\n");
84		count = -EBADMSG;
85	}
86	return count;
87}
88EXPORT_SYMBOL(nand_bch_correct_data);
89
90/**
91 * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
92 * @mtd:	MTD block structure
93 *
94 * Returns:
95 *  a pointer to a new NAND BCH control structure, or NULL upon failure
96 *
97 * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
98 * are used to compute BCH parameters m (Galois field order) and t (error
99 * correction capability). @eccbytes should be equal to the number of bytes
100 * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
101 *
102 * Example: to configure 4 bit correction per 512 bytes, you should pass
103 * @eccsize = 512  (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
104 * @eccbytes = 7   (7 bytes are required to store m*t = 13*4 = 52 bits)
105 */
106struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
107{
108	struct nand_chip *nand = mtd_to_nand(mtd);
109	unsigned int m, t, eccsteps, i;
110	struct nand_bch_control *nbc = NULL;
111	unsigned char *erased_page;
112	unsigned int eccsize = nand->ecc.size;
113	unsigned int eccbytes = nand->ecc.bytes;
114	unsigned int eccstrength = nand->ecc.strength;
115
116	if (!eccbytes && eccstrength) {
117		eccbytes = DIV_ROUND_UP(eccstrength * fls(8 * eccsize), 8);
118		nand->ecc.bytes = eccbytes;
119	}
120
121	if (!eccsize || !eccbytes) {
122		pr_warn("ecc parameters not supplied\n");
123		goto fail;
124	}
125
126	m = fls(1+8*eccsize);
127	t = (eccbytes*8)/m;
128
129	nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
130	if (!nbc)
131		goto fail;
132
133	nbc->bch = bch_init(m, t, 0, false);
134	if (!nbc->bch)
135		goto fail;
136
137	/* verify that eccbytes has the expected value */
138	if (nbc->bch->ecc_bytes != eccbytes) {
139		pr_warn("invalid eccbytes %u, should be %u\n",
140			eccbytes, nbc->bch->ecc_bytes);
141		goto fail;
142	}
143
144	eccsteps = mtd->writesize/eccsize;
145
146	/* Check that we have an oob layout description. */
147	if (!mtd->ooblayout) {
148		pr_warn("missing oob scheme");
149		goto fail;
150	}
151
152	/* sanity checks */
153	if (8*(eccsize+eccbytes) >= (1 << m)) {
154		pr_warn("eccsize %u is too large\n", eccsize);
155		goto fail;
156	}
157
158	/*
159	 * ecc->steps and ecc->total might be used by mtd->ooblayout->ecc(),
160	 * which is called by mtd_ooblayout_count_eccbytes().
161	 * Make sure they are properly initialized before calling
162	 * mtd_ooblayout_count_eccbytes().
163	 * FIXME: we should probably rework the sequencing in nand_scan_tail()
164	 * to avoid setting those fields twice.
165	 */
166	nand->ecc.steps = eccsteps;
167	nand->ecc.total = eccsteps * eccbytes;
168	nand->base.ecc.ctx.total = nand->ecc.total;
169	if (mtd_ooblayout_count_eccbytes(mtd) != (eccsteps*eccbytes)) {
170		pr_warn("invalid ecc layout\n");
171		goto fail;
172	}
173
174	nbc->eccmask = kzalloc(eccbytes, GFP_KERNEL);
175	nbc->errloc = kmalloc_array(t, sizeof(*nbc->errloc), GFP_KERNEL);
176	if (!nbc->eccmask || !nbc->errloc)
177		goto fail;
178	/*
179	 * compute and store the inverted ecc of an erased ecc block
180	 */
181	erased_page = kmalloc(eccsize, GFP_KERNEL);
182	if (!erased_page)
183		goto fail;
184
185	memset(erased_page, 0xff, eccsize);
186	bch_encode(nbc->bch, erased_page, eccsize, nbc->eccmask);
187	kfree(erased_page);
188
189	for (i = 0; i < eccbytes; i++)
190		nbc->eccmask[i] ^= 0xff;
191
192	if (!eccstrength)
193		nand->ecc.strength = (eccbytes * 8) / fls(8 * eccsize);
194
195	return nbc;
196fail:
197	nand_bch_free(nbc);
198	return NULL;
199}
200EXPORT_SYMBOL(nand_bch_init);
201
202/**
203 * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
204 * @nbc:	NAND BCH control structure
205 */
206void nand_bch_free(struct nand_bch_control *nbc)
207{
208	if (nbc) {
209		bch_free(nbc->bch);
210		kfree(nbc->errloc);
211		kfree(nbc->eccmask);
212		kfree(nbc);
213	}
214}
215EXPORT_SYMBOL(nand_bch_free);
216
217MODULE_LICENSE("GPL");
218MODULE_AUTHOR("Ivan Djelic <ivan.djelic@parrot.com>");
219MODULE_DESCRIPTION("NAND software BCH ECC support");
220