mtd: nand: DaVinci: Add 4-bit ECC support for large page NAND chips

This patch adds 4-bit ECC support for large page NAND chips using the new
ECC mode NAND_ECC_HW_OOB_FIRST.  The platform data from board-dm355-evm
has been adjusted to use this mode.

The patches have been verified on DM355 device with 2KiB-page Micron
devices using mtd-tests and JFFS2.  Error correction up to 4 bits has
also been verified using nandwrite/nanddump utilities.

Reviewed-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Sneha Narnakaje <nsnehaprabha@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index 0fad648..f13f5b9 100644 (file)
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -348,6 +348,12 @@ compare:
        if (!(syndrome[0] | syndrome[1] | syndrome[2] | syndrome[3]))
                return 0;
 
+       /*
+        * Clear any previous address calculation by doing a dummy read of an
+        * error address register.
+        */
+       davinci_nand_readl(info, NAND_ERR_ADD1_OFFSET);
+
        /* Start address calculation, and wait for it to complete.
         * We _could_ start reading more data while this is working,
         * to speed up the overall page read.
@@ -359,8 +365,10 @@ compare:
 
                switch ((fsr >> 8) & 0x0f) {
                case 0:         /* no error, should not happen */
+                       davinci_nand_readl(info, NAND_ERR_ERRVAL1_OFFSET);
                        return 0;
                case 1:         /* five or more errors detected */
+                       davinci_nand_readl(info, NAND_ERR_ERRVAL1_OFFSET);
                        return -EIO;
                case 2:         /* error addresses computed */
                case 3:
@@ -500,6 +508,26 @@ static struct nand_ecclayout hwecc4_small __initconst = {
        },
 };
 
+/* An ECC layout for using 4-bit ECC with large-page (2048bytes) flash,
+ * storing ten ECC bytes plus the manufacturer's bad block marker byte,
+ * and not overlapping the default BBT markers.
+ */
+static struct nand_ecclayout hwecc4_2048 __initconst = {
+       .eccbytes = 40,
+       .eccpos = {
+               /* at the end of spare sector */
+               24, 25, 26, 27, 28, 29, 30, 31, 32, 33,
+               34, 35, 36, 37, 38, 39, 40, 41, 42, 43,
+               44, 45, 46, 47, 48, 49, 50, 51, 52, 53,
+               54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
+               },
+       .oobfree = {
+               /* 2 bytes at offset 0 hold manufacturer badblock markers */
+               {.offset = 2, .length = 22, },
+               /* 5 bytes at offset 8 hold BBT markers */
+               /* 8 bytes at offset 16 hold JFFS2 clean markers */
+       },
+};
 
 static int __init nand_davinci_probe(struct platform_device *pdev)
 {
@@ -690,15 +718,20 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
                                info->mtd.oobsize - 16;
                        goto syndrome_done;
                }
+               if (chunks == 4) {
+                       info->ecclayout = hwecc4_2048;
+                       info->chip.ecc.mode = NAND_ECC_HW_OOB_FIRST;
+                       goto syndrome_done;
+               }
 
-               /* For large page chips we'll be wanting to use a
-                * not-yet-implemented mode that reads OOB data
-                * before reading the body of the page, to avoid
-                * the "infix OOB" model of NAND_ECC_HW_SYNDROME
-                * (and preserve manufacturer badblock markings).
+               /* 4KiB page chips are not yet supported. The eccpos from
+                * nand_ecclayout cannot hold 80 bytes and change to eccpos[]
+                * breaks userspace ioctl interface with mtd-utils. Once we
+                * resolve this issue, NAND_ECC_HW_OOB_FIRST mode can be used
+                * for the 4KiB page chips.
                 */
                dev_warn(&pdev->dev, "no 4-bit ECC support yet "
-                               "for large page NAND\n");
+                               "for 4KiB-page NAND\n");
                ret = -EIO;
                goto err_scan;