/*-
 * Copyright (C) 2009 Semihalf, Grzegorz Bernacki
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <dev/nand/nand_ecc.h>

#define BIT0(x) ((x) & 0x1)
#define BIT1(x) (BIT0(x >> 1))
#define BIT2(x) (BIT0(x >> 2))
#define BIT3(x) (BIT0(x >> 3))
#define BIT4(x) (BIT0(x >> 4))
#define BIT5(x) (BIT0(x >> 5))
#define BIT6(x) (BIT0(x >> 6))
#define BIT7(x) (BIT0(x >> 7))

void calculate_ecc(const uint8_t *buf, uint8_t *ecc)
{
	uint8_t p8, byte;
	int i;

	memset(ecc, 0, 3);

	for (i = 0; i < 256; i++) {
		byte = buf[i];
		ecc[0] ^= (BIT0(byte) ^ BIT2(byte) ^ BIT4(byte) ^
		    BIT6(byte)) << 2;
		ecc[0] ^= (BIT1(byte) ^ BIT3(byte) ^ BIT5(byte) ^
		    BIT7(byte)) << 3;
		ecc[0] ^= (BIT0(byte) ^ BIT1(byte) ^ BIT4(byte) ^
		    BIT5(byte)) << 4;
		ecc[0] ^= (BIT2(byte) ^ BIT3(byte) ^ BIT6(byte) ^
		    BIT7(byte)) << 5;
		ecc[0] ^= (BIT0(byte) ^ BIT1(byte) ^ BIT2(byte) ^
		    BIT3(byte)) << 6;
		ecc[0] ^= (BIT4(byte) ^ BIT5(byte) ^ BIT6(byte) ^
		    BIT7(byte)) << 7;

		p8 = BIT0(byte) ^ BIT1(byte) ^ BIT2(byte) ^
		    BIT3(byte) ^ BIT4(byte) ^ BIT5(byte) ^ BIT6(byte) ^
		    BIT7(byte);

		if (p8) {
			ecc[2] ^= (0x1 << BIT0(i));
			ecc[2] ^= (0x4 << BIT1(i));
			ecc[2] ^= (0x10 << BIT2(i));
			ecc[2] ^= (0x40 << BIT3(i));

			ecc[1] ^= (0x1 << BIT4(i));
			ecc[1] ^= (0x4 << BIT5(i));
			ecc[1] ^= (0x10 << BIT6(i));
			ecc[1] ^= (0x40 << BIT7(i));
		}
	}
	ecc[0] = ~ecc[0];
	ecc[1] = ~ecc[1];
	ecc[2] = ~ecc[2];
	ecc[0] |= 3;
}


int
correct_ecc(uint8_t *buf, uint8_t *calc_ecc, uint8_t *read_ecc)
{
	uint8_t ecc0, ecc1, ecc2, onesnum, bit, byte;
	uint16_t addr = 0;

	ecc0 = calc_ecc[0] ^ read_ecc[0];
	ecc1 = calc_ecc[1] ^ read_ecc[1];
	ecc2 = calc_ecc[2] ^ read_ecc[2];

	if (!ecc0 && !ecc1 && !ecc2)
		return (ECC_OK);

	addr = BIT3(ecc0) | (BIT5(ecc0) << 1) | (BIT7(ecc0) << 2);
	addr |= (BIT1(ecc2) << 3) | (BIT3(ecc2) << 4) |
		    (BIT5(ecc2) << 5) |  (BIT7(ecc2) << 6);
	addr |= (BIT1(ecc1) << 7) | (BIT3(ecc1) << 8) |
		    (BIT5(ecc1) << 9) |  (BIT7(ecc1) << 10);

	onesnum = 0;
	while (ecc0 || ecc1 || ecc2) {
		if (ecc0 & 1)
			onesnum++;
		if (ecc1 & 1)
			onesnum++;
		if (ecc2 & 1)
			onesnum++;

		ecc0 >>= 1;
		ecc1 >>= 1;
		ecc2 >>= 1;
	}

	if (onesnum == 11) {
		/* correctable error */
		bit = addr & 7;
		byte = addr >> 3;
		buf[byte] ^= (1 << bit);
		return (ECC_CORRECTABLE);
	} else if (onesnum == 1) {
		/* ecc error */
		return (ECC_ERROR_ECC);
	} else {
		/* uncorrectable error */
		return (ECC_UNCORRECTABLE);
	}

	return (0);
}