linux-kernel - [PATCH] nand: fix wrong default oob layout for small pages using soft ecc

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Message-Id: <20170705065109.7738-1-miquel.raynal@free-electrons.com>
Date:   Wed,  5 Jul 2017 08:51:09 +0200
From:   Miquel Raynal <miquel.raynal@...e-electrons.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Miquel Raynal <miquel.raynal@...e-electrons.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-mtd@...ts.infradead.org (open list:NAND FLASH SUBSYSTEM),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] nand: fix wrong default oob layout for small pages using soft ecc

When using soft ecc, if no ooblayout is given, the core automatically
uses one of the nand_ooblayout_{sp,lp}*() functions to determine the
layout inside the out of band data.

Until kernel version 4.6, struct nand_ecclayout was used for that
purpose. During the migration from 4.6 to 4.7, an error shown up in the
small page layout, in the case oob section is only 8 bytes long.

The layout was using three bytes (0, 1, 2) for ecc, two bytes (3, 4)
as free bytes, one byte (5) for bad block marker and finally
two bytes (6, 7) as free bytes, as shown there:

[linux-4.6] drivers/mtd/nand/nand_base.c:52
static struct nand_ecclayout nand_oob_8 = {
	.eccbytes = 3,
	.eccpos = {0, 1, 2},
	.oobfree = {
		{.offset = 3,
		 .length = 2},
		{.offset = 6,
		 .length = 2} }
};

This fixes the current implementation which is incoherent. It
references bit 3 at the same time as an ecc byte and a free byte.

Furthermore, it is clear with the previous implementation that there
is only one ecc section with 8 bytes oob sections. We shall return
-ERANGE in the nand_ooblayout_ecc_sp() function when asked for the
second section.

Signed-off-by: Miquel Raynal <miquel.raynal@...e-electrons.com>
---
 drivers/mtd/nand/nand_base.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b1dd12729f19..c5221795a1e8 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -65,8 +65,14 @@ static int nand_ooblayout_ecc_sp(struct mtd_info *mtd, int section,
 
 	if (!section) {
 		oobregion->offset = 0;
-		oobregion->length = 4;
+		if (mtd->oobsize == 16)
+			oobregion->length = 4;
+		else
+			oobregion->length = 3;
 	} else {
+		if (mtd->oobsize == 8)
+			return -ERANGE;
+
 		oobregion->offset = 6;
 		oobregion->length = ecc->total - 4;
 	}
-- 
2.11.0