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[MTD] [NAND] nand_ecc.c: adding support for 512 byte ecc
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Support 512 byte ECC calculation

[FM: updated two comments]

Signed-off-by: Vimal Singh <vimalsingh@ti.com>
Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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Singh, Vimal authored and David Woodhouse committed Aug 25, 2008
1 parent dffc8d6 commit d68156c
Showing 1 changed file with 62 additions and 24 deletions.
86 changes: 62 additions & 24 deletions drivers/mtd/nand/nand_ecc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,8 @@
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_ecc.h>
#include <asm/byteorder.h>
#else
Expand Down Expand Up @@ -148,8 +150,9 @@ static const char addressbits[256] = {
};

/**
* nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256-byte block
* @mtd: MTD block structure (unused)
* nand_calculate_ecc - [NAND Interface] Calculate 3-byte ECC for 256/512-byte
* block
* @mtd: MTD block structure
* @buf: input buffer with raw data
* @code: output buffer with ECC
*/
Expand All @@ -158,13 +161,18 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
{
int i;
const uint32_t *bp = (uint32_t *)buf;
/* 256 or 512 bytes/ecc */
const uint32_t eccsize_mult =
(((struct nand_chip *)mtd->priv)->ecc.size) >> 8;
uint32_t cur; /* current value in buffer */
/* rp0..rp15 are the various accumulated parities (per byte) */
/* rp0..rp15..rp17 are the various accumulated parities (per byte) */
uint32_t rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7;
uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15;
uint32_t rp8, rp9, rp10, rp11, rp12, rp13, rp14, rp15, rp16;
uint32_t uninitialized_var(rp17); /* to make compiler happy */
uint32_t par; /* the cumulative parity for all data */
uint32_t tmppar; /* the cumulative parity for this iteration;
for rp12 and rp14 at the end of the loop */
for rp12, rp14 and rp16 at the end of the
loop */

par = 0;
rp4 = 0;
Expand All @@ -173,6 +181,7 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
rp10 = 0;
rp12 = 0;
rp14 = 0;
rp16 = 0;

/*
* The loop is unrolled a number of times;
Expand All @@ -181,10 +190,10 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
* Note: passing unaligned data might give a performance penalty.
* It is assumed that the buffers are aligned.
* tmppar is the cumulative sum of this iteration.
* needed for calculating rp12, rp14 and par
* needed for calculating rp12, rp14, rp16 and par
* also used as a performance improvement for rp6, rp8 and rp10
*/
for (i = 0; i < 4; i++) {
for (i = 0; i < eccsize_mult << 2; i++) {
cur = *bp++;
tmppar = cur;
rp4 ^= cur;
Expand Down Expand Up @@ -247,12 +256,14 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
rp12 ^= tmppar;
if ((i & 0x2) == 0)
rp14 ^= tmppar;
if (eccsize_mult == 2 && (i & 0x4) == 0)
rp16 ^= tmppar;
}

/*
* handle the fact that we use longword operations
* we'll bring rp4..rp14 back to single byte entities by shifting and
* xoring first fold the upper and lower 16 bits,
* we'll bring rp4..rp14..rp16 back to single byte entities by
* shifting and xoring first fold the upper and lower 16 bits,
* then the upper and lower 8 bits.
*/
rp4 ^= (rp4 >> 16);
Expand All @@ -273,6 +284,11 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
rp14 ^= (rp14 >> 16);
rp14 ^= (rp14 >> 8);
rp14 &= 0xff;
if (eccsize_mult == 2) {
rp16 ^= (rp16 >> 16);
rp16 ^= (rp16 >> 8);
rp16 &= 0xff;
}

/*
* we also need to calculate the row parity for rp0..rp3
Expand Down Expand Up @@ -315,7 +331,7 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
par &= 0xff;

/*
* and calculate rp5..rp15
* and calculate rp5..rp15..rp17
* note that par = rp4 ^ rp5 and due to the commutative property
* of the ^ operator we can say:
* rp5 = (par ^ rp4);
Expand All @@ -329,6 +345,8 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
rp11 = (par ^ rp10) & 0xff;
rp13 = (par ^ rp12) & 0xff;
rp15 = (par ^ rp14) & 0xff;
if (eccsize_mult == 2)
rp17 = (par ^ rp16) & 0xff;

/*
* Finally calculate the ecc bits.
Expand Down Expand Up @@ -375,32 +393,46 @@ int nand_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
(invparity[rp9] << 1) |
(invparity[rp8]);
#endif
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
3;
if (eccsize_mult == 1)
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
3;
else
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
(invparity[rp17] << 1) |
(invparity[rp16] << 0);
return 0;
}
EXPORT_SYMBOL(nand_calculate_ecc);

/**
* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
* @mtd: MTD block structure (unused)
* @mtd: MTD block structure
* @buf: raw data read from the chip
* @read_ecc: ECC from the chip
* @calc_ecc: the ECC calculated from raw data
*
* Detect and correct a 1 bit error for 256 byte block
* Detect and correct a 1 bit error for 256/512 byte block
*/
int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
unsigned char *read_ecc, unsigned char *calc_ecc)
{
unsigned char b0, b1, b2;
unsigned char byte_addr, bit_addr;
/* 256 or 512 bytes/ecc */
const uint32_t eccsize_mult =
(((struct nand_chip *)mtd->priv)->ecc.size) >> 8;

/*
* b0 to b2 indicate which bit is faulty (if any)
Expand All @@ -426,10 +458,12 @@ int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,

if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
(((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
(((b2 ^ (b2 >> 1)) & 0x54) == 0x54)) { /* single bit error */
((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
(eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
/* 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.
* rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
* byte, cp 5/3/1 indicate the faulty bit.
* A lookup table (called addressbits) is used to filter
* the bits from the byte they are in.
* A marginal optimisation is possible by having three
Expand All @@ -443,7 +477,11 @@ int nand_correct_data(struct mtd_info *mtd, unsigned char *buf,
* We could also do addressbits[b2] >> 1 but for the
* performace it does not make any difference
*/
byte_addr = (addressbits[b1] << 4) + addressbits[b0];
if (eccsize_mult == 1)
byte_addr = (addressbits[b1] << 4) + addressbits[b0];
else
byte_addr = (addressbits[b2 & 0x3] << 8) +
(addressbits[b1] << 4) + addressbits[b0];
bit_addr = addressbits[b2 >> 2];
/* flip the bit */
buf[byte_addr] ^= (1 << bit_addr);
Expand Down

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