[MTD] [NAND] S3C2410: Hardware ECC correction code

Add support for correcting errors detected by the
hardware ECC.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index 9326a56..143a7f0 100644 (file)
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -126,10 +126,6 @@ config MTD_NAND_S3C2410_HWECC
          incorrect ECC generation, and if using these, the default of
          software ECC is preferable.
 
-         If you lay down a device with the hardware ECC, then you will
-         currently not be able to switch to software, as there is no
-         implementation for ECC method used by the S3C2410
-
 config MTD_NAND_NDFC
        tristate "NDFC NanD Flash Controller"
        depends on MTD_NAND && 44x

diff --git a/drivers/mtd/nand/s3c2410.c b/drivers/mtd/nand/s3c2410.c
index 8b32035..e8e0301 100644 (file)
--- a/drivers/mtd/nand/s3c2410.c
+++ b/drivers/mtd/nand/s3c2410.c
@@ -337,17 +337,69 @@ static int s3c2412_nand_devready(struct mtd_info *mtd)
 static int s3c2410_nand_correct_data(struct mtd_info *mtd, u_char *dat,
                                     u_char *read_ecc, u_char *calc_ecc)
 {
-       pr_debug("s3c2410_nand_correct_data(%p,%p,%p,%p)\n", mtd, dat, read_ecc, calc_ecc);
+       struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd);
+       unsigned int diff0, diff1, diff2;
+       unsigned int bit, byte;
 
-       pr_debug("eccs: read %02x,%02x,%02x vs calc %02x,%02x,%02x\n",
-                read_ecc[0], read_ecc[1], read_ecc[2], calc_ecc[0], calc_ecc[1], calc_ecc[2]);
+       pr_debug("%s(%p,%p,%p,%p)\n", __func__, mtd, dat, read_ecc, calc_ecc);
 
-       if (read_ecc[0] == calc_ecc[0] && read_ecc[1] == calc_ecc[1] && read_ecc[2] == calc_ecc[2])
-               return 0;
+       diff0 = read_ecc[0] ^ calc_ecc[0];
+       diff1 = read_ecc[1] ^ calc_ecc[1];
+       diff2 = read_ecc[2] ^ calc_ecc[2];
+
+       pr_debug("%s: rd %02x%02x%02x calc %02x%02x%02x diff %02x%02x%02x\n",
+                __func__,
+                read_ecc[0], read_ecc[1], read_ecc[2],
+                calc_ecc[0], calc_ecc[1], calc_ecc[2],
+                diff0, diff1, diff2);
+
+       if (diff0 == 0 && diff1 == 0 && diff2 == 0)
+               return 0;               /* ECC is ok */
+
+       /* Can we correct this ECC (ie, one row and column change).
+        * Note, this is similar to the 256 error code on smartmedia */
+
+       if (((diff0 ^ (diff0 >> 1)) & 0x55) == 0x55 &&
+           ((diff1 ^ (diff1 >> 1)) & 0x55) == 0x55 &&
+           ((diff2 ^ (diff2 >> 1)) & 0x55) == 0x55) {
+               /* calculate the bit position of the error */
+
+               bit  = (diff2 >> 2) & 1;
+               bit |= (diff2 >> 3) & 2;
+               bit |= (diff2 >> 4) & 4;
+
+               /* calculate the byte position of the error */
+
+               byte  = (diff1 << 1) & 0x80;
+               byte |= (diff1 << 2) & 0x40;
+               byte |= (diff1 << 3) & 0x20;
+               byte |= (diff1 << 4) & 0x10;
 
-       /* we curently have no method for correcting the error */
+               byte |= (diff0 >> 3) & 0x08;
+               byte |= (diff0 >> 2) & 0x04;
+               byte |= (diff0 >> 1) & 0x02;
+               byte |= (diff0 >> 0) & 0x01;
 
-       return -1;
+               byte |= (diff2 << 8) & 0x100;
+
+               dev_dbg(info->device, "correcting error bit %d, byte %d\n",
+                       bit, byte);
+
+               dat[byte] ^= (1 << bit);
+               return 1;
+       }
+
+       /* if there is only one bit difference in the ECC, then
+        * one of only a row or column parity has changed, which
+        * means the error is most probably in the ECC itself */
+
+       diff0 |= (diff1 << 8);
+       diff0 |= (diff2 << 16);
+
+       if ((diff0 & ~(1<<fls(diff0))) == 0)
+               return 1;
+
+       return 0;
 }
 
 /* ECC functions
@@ -383,7 +435,8 @@ static int s3c2410_nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u
        ecc_code[1] = readb(info->regs + S3C2410_NFECC + 1);
        ecc_code[2] = readb(info->regs + S3C2410_NFECC + 2);
 
-       pr_debug("calculate_ecc: returning ecc %02x,%02x,%02x\n", ecc_code[0], ecc_code[1], ecc_code[2]);
+       pr_debug("%s: returning ecc %02x%02x%02x\n", __func__,
+                ecc_code[0], ecc_code[1], ecc_code[2]);
 
        return 0;
 }
@@ -397,7 +450,7 @@ static int s3c2440_nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u
        ecc_code[1] = ecc >> 8;
        ecc_code[2] = ecc >> 16;
 
-       pr_debug("calculate_ecc: returning ecc %02x,%02x,%02x\n", ecc_code[0], ecc_code[1], ecc_code[2]);
+       pr_debug("%s: returning ecc %06x\n", __func__, ecc);
 
        return 0;
 }