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Commit 1077be58 authored by frans's avatar frans Committed by David Woodhouse
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[MTD] [NAND] nand_ecc.c: fix big endian, strengthen test, add printk 



This patch for nand_ecc.c fixes three issues

- fix code so it also works on big endian architectures
- added a printk in case of an uncorrectable ecc error
- strengthen the test for correctable errors (decreasing the chance
  that multiple bit faults by accident will be seen as correctable)

Note: the big endian code is only tested in a testbed (running on big endian
hardware) as I cannot rebuild and test a big endian kernel at the moment.
However the only thing that can go wrong is if <asm/byteorder.h> does not
give __BIG_ENDIAN in that case. In my eyes very unlikely.

Signed-off-by: default avatarFrans Meulenbroeks <fransmeulenbroeks@gmail.com>
Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
parent 75caf6b5

drivers/mtd/nand/nand_ecc.c

+33 −11
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ 
#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/mtd/nand_ecc.h>

#include <asm/byteorder.h>

#else

#include <stdint.h>

struct mtd_info;
@@ -51,6 +52,9 @@ struct mtd_info; 
#define MODULE_LICENSE(x)	/* x */

#define MODULE_AUTHOR(x)	/* x */

#define MODULE_DESCRIPTION(x)	/* x */



#define printk printf

#define KERN_ERR		""

#endif



/*
@@ -273,24 +277,38 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf, 
	/*

	 * we also need to calculate the row parity for rp0..rp3

	 * This is present in par, because par is now

	 * rp3 rp3 rp2 rp2

	 * rp3 rp3 rp2 rp2 in little endian and

	 * rp2 rp2 rp3 rp3 in big endian

	 * as well as

	 * rp1 rp0 rp1 rp0

	 * rp1 rp0 rp1 rp0 in little endian and

	 * rp0 rp1 rp0 rp1 in big endian

	 * First calculate rp2 and rp3

	 * (and yes: rp2 = (par ^ rp3) & 0xff; but doing that did not

	 * give a performance improvement)

	 */

#ifdef __BIG_ENDIAN

	rp2 = (par >> 16);

	rp2 ^= (rp2 >> 8);

	rp2 &= 0xff;

	rp3 = par & 0xffff;

	rp3 ^= (rp3 >> 8);

	rp3 &= 0xff;

#else

	rp3 = (par >> 16);

	rp3 ^= (rp3 >> 8);

	rp3 &= 0xff;

	rp2 = par & 0xffff;

	rp2 ^= (rp2 >> 8);

	rp2 &= 0xff;

#endif



	/* reduce par to 16 bits then calculate rp1 and rp0 */

	par ^= (par >> 16);

#ifdef __BIG_ENDIAN

	rp0 = (par >> 8) & 0xff;

	rp1 = (par & 0xff);

#else

	rp1 = (par >> 8) & 0xff;

	rp0 = (par & 0xff);

#endif



	/* finally reduce par to 8 bits */

	par ^= (par >> 8);
@@ -381,7 +399,6 @@ EXPORT_SYMBOL(nand_calculate_ecc); 
int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,

		      unsigned char *read_ecc, unsigned char *calc_ecc)

{

	int nr_bits;

	unsigned char b0, b1, b2;

	unsigned char byte_addr, bit_addr;
@@ -401,14 +418,15 @@ int nand_correct_data(struct mtd_info *mtd, unsigned char *buf, 


	/* check if there are any bitfaults */



	/* count nr of bits; use table lookup, faster than calculating it */

	nr_bits = bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2];



	/* repeated if statements are slightly more efficient than switch ... */

	/* ordered in order of likelihood */

	if (nr_bits == 0)



	if ((b0 | b1 | b2) == 0)

		return 0;	/* no error */

	if (nr_bits == 11) {	/* correctable error */



	if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&

	    (((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&

	    (((b2 ^ (b2 >> 1)) & 0x54) == 0x54)) { /* single bit error */

		/*

		 * rp15/13/11/9/7/5/3/1 indicate which byte is the faulty byte

		 * cp 5/3/1 indicate the faulty bit.
@@ -430,9 +448,13 @@ int nand_correct_data(struct mtd_info *mtd, unsigned char *buf, 
		/* flip the bit */

		buf[byte_addr] ^= (1 << bit_addr);

		return 1;



	}

	if (nr_bits == 1)

	/* count nr of bits; use table lookup, faster than calculating it */

	if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)

		return 1;	/* error in ecc data; no action needed */



	printk(KERN_ERR "uncorrectable error : ");

	return -1;

}

EXPORT_SYMBOL(nand_correct_data);