[PATCH] mtd: nand: davinci: Fix unaligned 16-bit NAND read

[Ville Michael Baillie]

This patch fixes a rare bug when reading from 16-bit NAND flashes, by
not allowing 8-bit read accesses within nand_davinci_read_buf().

In certain situations, an non 16-bit aligned buffer is passed to
nand_davinci_read_buf(), which causes 8-bit accesses to be performed.
However, the NAND will be returning 16-bit words, and half of these will
be discarded.

This was observed when running mtd_stresstest.ko, which would report ECC
errors when reading from a non 16-bit aligned offset into a page, and
reading at least one subsequent page in the same read.

Signed-off-by: Ville Michael Baillie <ville.michael.baillie at gmail.com>
---
 drivers/mtd/nand/davinci_nand.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index 27fa8b8..ed9cd0d 100644
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -442,12 +442,24 @@ static int nand_davinci_correct_4bit(struct mtd_info *mtd,
 static void nand_davinci_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
 {
 	struct nand_chip *chip = mtd_to_nand(mtd);
+	u16 tmp;
 
 	if ((0x03 & ((unsigned)buf)) == 0 && (0x03 & len) == 0)
 		ioread32_rep(chip->IO_ADDR_R, buf, len >> 2);
 	else if ((0x01 & ((unsigned)buf)) == 0 && (0x01 & len) == 0)
 		ioread16_rep(chip->IO_ADDR_R, buf, len >> 1);
-	else
+	else if (chip->options & NAND_BUSWIDTH_16) {
+		/*
+		 * if NAND buswidth is 16 then 8 bit accesses
+		 * will silently discard half the data
+		 */
+		len /= 2;
+		while (len--) {
+			tmp = ioread16(chip->IO_ADDR_R);
+			memcpy(buf, &tmp, sizeof(u16));
+			buf += sizeof(u16);
+		}
+	} else
 		ioread8_rep(chip->IO_ADDR_R, buf, len);
 }
 
-- 
2.1.4