[PATCH] nand_read_subpage vs. S3C244x NAND: non-word reads

[Werner Almesberger <werner@openmoko.org>]

In recent kernels, the optimized OOB reads in nand_read_subpage often
make requests which aren't an exact multiple of a word, which caused
nand/s3c2410.c to do a partial read, yielding chaos and mayhem.

I'm not entirely sure whether nand_read_subpage is to blame for making
non-word requests, or whether nand/s3c2410.c is to blame for not
supporting them, but here's a patch for the latter.

Note that s3c2410_nand_write_buf has a similar issue. RNDIN is used in
nand_write_oob_syndrome, so this may also be a real problems.

- Werner

---------------------------------- cut here -----------------------------------

fix-s3c-nand-read-bytes.patch

With the introduction of optimized OOB reads in nand_read_subpage,
the length of the data requested may not be a multiple of four bytes.

This caused a partial read on the 2440, leading to false ECC errors
and, worse, attempts to "correct" them.

Note that there is a similar issue in s3c2440_nand_write_buf, which
doesn't seem to cause trouble yet.

Signed-off-by: Werner Almesberger <werner@openmoko.org>

---

Index: ktrack/drivers/mtd/nand/s3c2410.c
===================================================================
--- ktrack.orig/drivers/mtd/nand/s3c2410.c	2008-11-01 00:29:45.000000000 -0200
+++ ktrack/drivers/mtd/nand/s3c2410.c	2008-11-01 00:38:10.000000000 -0200
@@ -530,7 +530,14 @@
 static void s3c2440_nand_read_buf(struct mtd_info *mtd, u_char *buf, int len)
 {
 	struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd);
+
 	readsl(info->regs + S3C2440_NFDATA, buf, len / 4);
+	if (unlikely(len & 3)) {
+		u32 data;
+
+		data = readl(info->regs + S3C2440_NFDATA);
+		memcpy(buf + (len & ~3), &data, len & 3);
+	}
 }
 
 static void s3c2410_nand_write_buf(struct mtd_info *mtd, const u_char *buf, int len)