mtd: omap: fix subpage ecc issue with prefetch

When reading/writing a subpage (When HW ECC is not available/enabled)
for number of bytes not aligned to 4, the mis-aligned bytes are handled
first (by cpu copy method) before enabling the Prefetch engine to/from
'p'(start of buffer 'buf'). Then it reads/writes rest of the bytes with
the help of Prefetch engine, if available, or again using cpu copy method.
Currently, reading/writing of rest of bytes, is not done correctly since
its trying to read/write again to/from begining of buffer 'buf',
overwriting the mis-aligned bytes.

Read & write using prefetch engine got broken in commit '2c01946c'.
We never hit a scenario of not getting 'gpmc_prefetch_enable' call
success. So, problem did not get caught up.
Signed-off-by: Kishore Kadiyala <kishore.kadiyala@ti.com>
Signed-off-by: Vimal Singh <vimal.newwork@gmail.com>
Reported-by: Bryan DE FARIA <bdefaria@adeneo-embedded.com>
Cc: stable@kernel.org [2.6.35+]
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/omap2.c

@@ -263,11 +263,10 @@ static void omap_read_buf_pref(struct mtd_info *mtd, u_char *buf, int len)
 	if (ret) {
 		/* PFPW engine is busy, use cpu copy method */
 		if (info->nand.options & NAND_BUSWIDTH_16)
-			omap_read_buf16(mtd, buf, len);
+			omap_read_buf16(mtd, (u_char *)p, len);
 		else
-			omap_read_buf8(mtd, buf, len);
+			omap_read_buf8(mtd, (u_char *)p, len);
 	} else {
-		p = (u32 *) buf;
 		do {
 			r_count = gpmc_read_status(GPMC_PREFETCH_FIFO_CNT);
 			r_count = r_count >> 2;
@@ -293,7 +292,7 @@ static void omap_write_buf_pref(struct mtd_info *mtd,
 						struct omap_nand_info, mtd);
 	uint32_t w_count = 0;
 	int i = 0, ret = 0;
-	u16 *p;
+	u16 *p = (u16 *)buf;
 	unsigned long tim, limit;
 
 	/* take care of subpage writes */
@@ -309,11 +308,10 @@ static void omap_write_buf_pref(struct mtd_info *mtd,
 	if (ret) {
 		/* PFPW engine is busy, use cpu copy method */
 		if (info->nand.options & NAND_BUSWIDTH_16)
-			omap_write_buf16(mtd, buf, len);
+			omap_write_buf16(mtd, (u_char *)p, len);
 		else
-			omap_write_buf8(mtd, buf, len);
+			omap_write_buf8(mtd, (u_char *)p, len);
 	} else {
-		p = (u16 *) buf;
 		while (len) {
 			w_count = gpmc_read_status(GPMC_PREFETCH_FIFO_CNT);
 			w_count = w_count >> 1;