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[MTD] [NAND] nand_ecc.c: fix big endian, strengthen test, add printk

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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: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
This commit is contained in:
frans 2008-08-20 21:11:50 +02:00 committed by David Woodhouse
parent 75caf6b5ac
commit 1077be58ad
1 changed files with 33 additions and 11 deletions
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44
drivers/mtd/nand/nand_ecc.c
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@ -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);