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>

1 files changed, 39 insertions, 6 deletions

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index 0fad6487e6f4..f13f5b9afaf7 100644
--- 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;