Messages in this thread Patch in this message | | | Date | Sat, 24 Mar 2012 18:38:30 +0800 | From | Zhaoxiu Zeng <> | Subject | [PATCH] mtd/nand/nand_ecc.c: replace bitsperbyte table by a simple operation |
| |
Signed-off-by: Zhaoxiu Zeng <zengzhaoxiu@163.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
| |