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Date: Sat, 24 Mar 2012 18:38:30 +0800
From: Zhaoxiu Zeng <zengzhaoxiu@....com>
To: linux-mtd@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] mtd/nand/nand_ecc.c: replace bitsperbyte table by a simple
operation
Signed-off-by: Zhaoxiu Zeng <zengzhaoxiu@....com>
---
drivers/mtd/nand/nand_ecc.c | 50 +++++++++---------------------------------
1 files changed, 11 insertions(+), 39 deletions(-)
diff --git a/drivers/mtd/nand/nand_ecc.c b/drivers/mtd/nand/nand_ecc.c
index b7cfe0d..e05a0fd 100644
--- a/drivers/mtd/nand/nand_ecc.c
+++ b/drivers/mtd/nand/nand_ecc.c
@@ -85,30 +85,6 @@ static const char invparity[256] = {
};
/*
- * bitsperbyte contains the number of bits per byte
- * this is only used for testing and repairing parity
- * (a precalculated value slightly improves performance)
- */
-static const char bitsperbyte[256] = {
- 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
- 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
- 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
- 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
- 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
- 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
- 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
- 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
-};
-
-/*
* addressbits is a lookup table to filter out the bits from the xor-ed
* ECC data that identify the faulty location.
* this is only used for repairing parity
@@ -448,12 +424,14 @@ int __nand_correct_data(unsigned char *buf,
unsigned int byte_addr;
/* 256 or 512 bytes/ecc */
const uint32_t eccsize_mult = eccsize >> 8;
+ const uint32_t check_mask = eccsize_mult == 2 ? 0x555555 : 0x545555;
+ uint32_t tmp;
/*
* b0 to b2 indicate which bit is faulty (if any)
* we might need the xor result more than once,
* so keep them in a local var
- */
+ */
#ifdef CONFIG_MTD_NAND_ECC_SMC
b0 = read_ecc[0] ^ calc_ecc[0];
b1 = read_ecc[1] ^ calc_ecc[1];
@@ -467,14 +445,11 @@ int __nand_correct_data(unsigned char *buf,
/* repeated if statements are slightly more efficient than switch ... */
/* ordered in order of likelihood */
-
- if ((b0 | b1 | b2) == 0)
+ tmp = ((uint32_t)b2 << 16) | ((uint32_t)b1 << 8) | b0;
+ if (tmp == 0)
return 0; /* no error */
- if ((((b0 ^ (b0 >> 1)) & 0x55) == 0x55) &&
- (((b1 ^ (b1 >> 1)) & 0x55) == 0x55) &&
- ((eccsize_mult == 1 && ((b2 ^ (b2 >> 1)) & 0x54) == 0x54) ||
- (eccsize_mult == 2 && ((b2 ^ (b2 >> 1)) & 0x55) == 0x55))) {
+ if (((tmp ^ (tmp >> 1)) & check_mask) == check_mask) {
/* single bit error */
/*
* rp17/rp15/13/11/9/7/5/3/1 indicate which byte is the faulty
@@ -492,19 +467,16 @@ int __nand_correct_data(unsigned char *buf,
* We could also do addressbits[b2] >> 1 but for the
* performance it does not make any difference
*/
- if (eccsize_mult == 1)
- byte_addr = (addressbits[b1] << 4) + addressbits[b0];
- else
- byte_addr = (addressbits[b2 & 0x3] << 8) +
- (addressbits[b1] << 4) + addressbits[b0];
+ byte_addr = (addressbits[b1] << 4) + addressbits[b0];
+ if (eccsize_mult == 2)
+ byte_addr += (addressbits[b2 & 0x3] << 8);
bit_addr = addressbits[b2 >> 2];
/* flip the bit */
buf[byte_addr] ^= (1 << bit_addr);
return 1;
-
}
- /* count nr of bits; use table lookup, faster than calculating it */
- if ((bitsperbyte[b0] + bitsperbyte[b1] + bitsperbyte[b2]) == 1)
+
+ if (!(tmp & (tmp - 1)))
return 1; /* error in ECC data; no action needed */
printk(KERN_ERR "uncorrectable error : ");
--
1.7.7.6
--
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