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It seems that several hardware ECC engine use a swapped representation
of bytes compared to software. This might having to do with how the
ECC engine is wired to the NAND controller or the order the bits are
passed to the hardware BCH logic.
This means that when the software BCH engine is working in conjunction
with data generated with hardware, sometimes we might need to swap the
bits inside bytes, eg:
0x0A = b0000_1010 -> b0101_0000 = 0x50
Make it possible by adding a boolean to the BCH initialization routine.
Regarding the implementation itself, this is a rather simple approach
that can probably be enhanced in the future by preparing the
->a_{mod,pow}_tab tables with the swapping in mind.
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200519074549.23673-3-miquel.raynal@bootlin.com
70 lines
2.1 KiB
C
70 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Generic binary BCH encoding/decoding library
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*
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* Copyright © 2011 Parrot S.A.
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*
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* Author: Ivan Djelic <ivan.djelic@parrot.com>
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*
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* Description:
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*
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* This library provides runtime configurable encoding/decoding of binary
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* Bose-Chaudhuri-Hocquenghem (BCH) codes.
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*/
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#ifndef _BCH_H
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#define _BCH_H
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#include <linux/types.h>
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/**
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* struct bch_control - BCH control structure
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* @m: Galois field order
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* @n: maximum codeword size in bits (= 2^m-1)
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* @t: error correction capability in bits
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* @ecc_bits: ecc exact size in bits, i.e. generator polynomial degree (<=m*t)
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* @ecc_bytes: ecc max size (m*t bits) in bytes
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* @a_pow_tab: Galois field GF(2^m) exponentiation lookup table
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* @a_log_tab: Galois field GF(2^m) log lookup table
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* @mod8_tab: remainder generator polynomial lookup tables
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* @ecc_buf: ecc parity words buffer
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* @ecc_buf2: ecc parity words buffer
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* @xi_tab: GF(2^m) base for solving degree 2 polynomial roots
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* @syn: syndrome buffer
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* @cache: log-based polynomial representation buffer
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* @elp: error locator polynomial
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* @poly_2t: temporary polynomials of degree 2t
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* @swap_bits: swap bits within data and syndrome bytes
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*/
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struct bch_control {
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unsigned int m;
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unsigned int n;
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unsigned int t;
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unsigned int ecc_bits;
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unsigned int ecc_bytes;
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/* private: */
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uint16_t *a_pow_tab;
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uint16_t *a_log_tab;
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uint32_t *mod8_tab;
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uint32_t *ecc_buf;
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uint32_t *ecc_buf2;
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unsigned int *xi_tab;
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unsigned int *syn;
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int *cache;
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struct gf_poly *elp;
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struct gf_poly *poly_2t[4];
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bool swap_bits;
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};
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struct bch_control *bch_init(int m, int t, unsigned int prim_poly,
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bool swap_bits);
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void bch_free(struct bch_control *bch);
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void bch_encode(struct bch_control *bch, const uint8_t *data,
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unsigned int len, uint8_t *ecc);
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int bch_decode(struct bch_control *bch, const uint8_t *data, unsigned int len,
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const uint8_t *recv_ecc, const uint8_t *calc_ecc,
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const unsigned int *syn, unsigned int *errloc);
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#endif /* _BCH_H */
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