[MTD] Improve software ECC calculation
Unrolling the loops produces denser and much faster code.
Add a config switch which allows to select the byte order of the
resulting ecc code. The current Linux implementation has a byte
swap versus the SmartMedia specification
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/drivers/mtd/nand/nand_ecc.c b/drivers/mtd/nand/nand_ecc.c
index 1018929..2a163e4 100644
--- a/drivers/mtd/nand/nand_ecc.c
+++ b/drivers/mtd/nand/nand_ecc.c
@@ -7,6 +7,8 @@
* Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
* Toshiba America Electronics Components, Inc.
*
+ * Copyright (C) 2006 Thomas Gleixner <tglx@linutronix.de>
+ *
* $Id: nand_ecc.c,v 1.15 2005/11/07 11:14:30 gleixner Exp $
*
* This file is free software; you can redistribute it and/or modify it
@@ -63,87 +65,75 @@
};
/**
- * nand_trans_result - [GENERIC] create non-inverted ECC
- * @reg2: line parity reg 2
- * @reg3: line parity reg 3
- * @ecc_code: ecc
- *
- * Creates non-inverted ECC code from line parity
- */
-static void nand_trans_result(u_char reg2, u_char reg3, u_char *ecc_code)
-{
- u_char a, b, i, tmp1, tmp2;
-
- /* Initialize variables */
- a = b = 0x80;
- tmp1 = tmp2 = 0;
-
- /* Calculate first ECC byte */
- for (i = 0; i < 4; i++) {
- if (reg3 & a) /* LP15,13,11,9 --> ecc_code[0] */
- tmp1 |= b;
- b >>= 1;
- if (reg2 & a) /* LP14,12,10,8 --> ecc_code[0] */
- tmp1 |= b;
- b >>= 1;
- a >>= 1;
- }
-
- /* Calculate second ECC byte */
- b = 0x80;
- for (i = 0; i < 4; i++) {
- if (reg3 & a) /* LP7,5,3,1 --> ecc_code[1] */
- tmp2 |= b;
- b >>= 1;
- if (reg2 & a) /* LP6,4,2,0 --> ecc_code[1] */
- tmp2 |= b;
- b >>= 1;
- a >>= 1;
- }
-
- /* Store two of the ECC bytes */
- ecc_code[0] = tmp1;
- ecc_code[1] = tmp2;
-}
-
-/**
- * nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code for 256 byte block
+ * nand_calculate_ecc - [NAND Interface] Calculate 3 byte ECC code
+ * for 256 byte block
* @mtd: MTD block structure
* @dat: raw data
* @ecc_code: buffer for ECC
*/
-int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
+int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
+ u_char *ecc_code)
{
- u_char idx, reg1, reg2, reg3;
- int j;
+ uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
+ int i;
/* Initialize variables */
reg1 = reg2 = reg3 = 0;
- ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
/* Build up column parity */
- for (j = 0; j < 256; j++) {
-
+ for(i = 0; i < 256; i++) {
/* Get CP0 - CP5 from table */
- idx = nand_ecc_precalc_table[dat[j]];
+ idx = nand_ecc_precalc_table[*dat++];
reg1 ^= (idx & 0x3f);
/* All bit XOR = 1 ? */
if (idx & 0x40) {
- reg3 ^= (u_char) j;
- reg2 ^= ~((u_char) j);
+ reg3 ^= (uint8_t) i;
+ reg2 ^= ~((uint8_t) i);
}
}
/* Create non-inverted ECC code from line parity */
- nand_trans_result(reg2, reg3, ecc_code);
+ tmp1 = (reg3 & 0x80) >> 0; /* B7 -> B7 */
+ tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */
+ tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */
+ tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */
+ tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */
+ tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */
+ tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */
+ tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */
+
+ tmp2 = (reg3 & 0x08) << 4; /* B3 -> B7 */
+ tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */
+ tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */
+ tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */
+ tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */
+ tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */
+ tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */
+ tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */
/* Calculate final ECC code */
- ecc_code[0] = ~ecc_code[0];
- ecc_code[1] = ~ecc_code[1];
+#ifdef CONFIG_NAND_ECC_SMC
+ ecc_code[0] = ~tmp2;
+ ecc_code[1] = ~tmp1;
+#else
+ ecc_code[0] = ~tmp1;
+ ecc_code[1] = ~tmp2;
+#endif
ecc_code[2] = ((~reg1) << 2) | 0x03;
+
return 0;
}
+EXPORT_SYMBOL(nand_calculate_ecc);
+
+static inline int countbits(uint32_t byte)
+{
+ int res = 0;
+
+ for (;byte; byte >>= 1)
+ res += byte & 0x01;
+ return res;
+}
/**
* nand_correct_data - [NAND Interface] Detect and correct bit error(s)
@@ -154,90 +144,54 @@
*
* Detect and correct a 1 bit error for 256 byte block
*/
-int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
+int nand_correct_data(struct mtd_info *mtd, u_char *dat,
+ u_char *read_ecc, u_char *calc_ecc)
{
- u_char a, b, c, d1, d2, d3, add, bit, i;
+ uint8_t s0, s1, s2;
- /* Do error detection */
- d1 = calc_ecc[0] ^ read_ecc[0];
- d2 = calc_ecc[1] ^ read_ecc[1];
- d3 = calc_ecc[2] ^ read_ecc[2];
-
- if ((d1 | d2 | d3) == 0) {
- /* No errors */
+#ifdef CONFIG_NAND_ECC_SMC
+ s0 = calc_ecc[0] ^ read_ecc[0];
+ s1 = calc_ecc[1] ^ read_ecc[1];
+ s2 = calc_ecc[2] ^ read_ecc[2];
+#else
+ s1 = calc_ecc[0] ^ read_ecc[0];
+ s0 = calc_ecc[1] ^ read_ecc[1];
+ s2 = calc_ecc[2] ^ read_ecc[2];
+#endif
+ if ((s0 | s1 | s2) == 0)
return 0;
- } else {
- a = (d1 ^ (d1 >> 1)) & 0x55;
- b = (d2 ^ (d2 >> 1)) & 0x55;
- c = (d3 ^ (d3 >> 1)) & 0x54;
- /* Found and will correct single bit error in the data */
- if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
- c = 0x80;
- add = 0;
- a = 0x80;
- for (i = 0; i < 4; i++) {
- if (d1 & c)
- add |= a;
- c >>= 2;
- a >>= 1;
- }
- c = 0x80;
- for (i = 0; i < 4; i++) {
- if (d2 & c)
- add |= a;
- c >>= 2;
- a >>= 1;
- }
- bit = 0;
- b = 0x04;
- c = 0x80;
- for (i = 0; i < 3; i++) {
- if (d3 & c)
- bit |= b;
- c >>= 2;
- b >>= 1;
- }
- b = 0x01;
- a = dat[add];
- a ^= (b << bit);
- dat[add] = a;
- return 1;
- } else {
- i = 0;
- while (d1) {
- if (d1 & 0x01)
- ++i;
- d1 >>= 1;
- }
- while (d2) {
- if (d2 & 0x01)
- ++i;
- d2 >>= 1;
- }
- while (d3) {
- if (d3 & 0x01)
- ++i;
- d3 >>= 1;
- }
- if (i == 1) {
- /* ECC Code Error Correction */
- read_ecc[0] = calc_ecc[0];
- read_ecc[1] = calc_ecc[1];
- read_ecc[2] = calc_ecc[2];
- return 2;
- } else {
- /* Uncorrectable Error */
- return -1;
- }
- }
+ /* Check for a single bit error */
+ if( ((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
+ ((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
+ ((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {
+
+ uint32_t byteoffs, bitnum;
+
+ byteoffs = (s1 << 0) & 0x80;
+ byteoffs |= (s1 << 1) & 0x40;
+ byteoffs |= (s1 << 2) & 0x20;
+ byteoffs |= (s1 << 3) & 0x10;
+
+ byteoffs |= (s0 >> 4) & 0x08;
+ byteoffs |= (s0 >> 3) & 0x04;
+ byteoffs |= (s0 >> 2) & 0x02;
+ byteoffs |= (s0 >> 1) & 0x01;
+
+ bitnum = (s2 >> 5) & 0x04;
+ bitnum |= (s2 >> 4) & 0x02;
+ bitnum |= (s2 >> 3) & 0x01;
+
+ dat[byteoffs] ^= (1 << bitnum);
+
+ return 1;
}
- /* Should never happen */
+ if(countbits(s0 | ((uint32_t)s1 << 8) | ((uint32_t)s2 <<16)) == 1)
+ return 1;
+
return -1;
}
-
-EXPORT_SYMBOL(nand_calculate_ecc);
EXPORT_SYMBOL(nand_correct_data);
MODULE_LICENSE("GPL");