linux-kernel - [PATCH v4] mtd: nand: Add OOB layout without ECC bytes

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Date:   Thu, 24 Aug 2017 10:35:38 +0200
From:   Miquel Raynal <miquel.raynal@...e-electrons.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-kernel@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...e-electrons.com>
Subject: [PATCH v4] mtd: nand: Add OOB layout without ECC bytes

Add layout functions for large pages with mainly free bytes
plus reserved space for Bad Block Markers. This may be useful for
configurations that does set ECC_NONE. Specific chips that use
on-die ECC feature, ie. the TOSHIBA BENAND (Built-in ECC NAND),
might also take advantage of it: the ECC bytes are stored in an
isolated area inaccessible by the driver and thus the OOB layout must
only reserve space for bad block markers.

Bad block markers position was extracted from the existing OOB layouts
by assigning as free all the bytes marked as ECC.

Normally, if NAND_ECC_NONE is chosen, the MTD user can use the whole OOB
area (except the bytes reserved for the bad block markers) to store
private data, but the NAND framework has been using the same OOB layout
(the one reserving ECC bytes) no matter whether ECC is enabled or not.
In order to not break existing MTD users which may rely on this layout
to work properly, we keep things unchanged and only use the 'no_ecc'
layouts for previously unsupported configurations.

Signed-off-by: Miquel Raynal <miquel.raynal@...e-electrons.com>
---
 drivers/mtd/nand/nand_base.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index c5221795a1e8..ef40866d3435 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -109,6 +109,22 @@ const struct mtd_ooblayout_ops nand_ooblayout_sp_ops = {
 };
 EXPORT_SYMBOL_GPL(nand_ooblayout_sp_ops);

+static int nand_ooblayout_free_lp_no_ecc(struct mtd_info *mtd, int section,
+					   struct mtd_oob_region *oobregion)
+{
+	if (section)
+		return -ERANGE;
+
+	oobregion->offset = 2;
+	oobregion->length = mtd->oobsize - oobregion->offset;
+
+	return 0;
+}
+
+const struct mtd_ooblayout_ops nand_ooblayout_lp_no_ecc_ops = {
+	.free = nand_ooblayout_free_lp_no_ecc,
+};
+
 static int nand_ooblayout_ecc_lp(struct mtd_info *mtd, int section,
 				 struct mtd_oob_region *oobregion)
 {
@@ -4649,6 +4665,19 @@ int nand_scan_tail(struct mtd_info *mtd)
 			mtd_set_ooblayout(mtd, &nand_ooblayout_lp_hamming_ops);
 			break;
 		default:
+			/*
+			 * Expose the whole OOB area to users if ECC_NONE
+			 * is passed. We could do that for all kind of
+			 * ->oobsize, but we must keep the old large/small
+			 * page with ECC layout when ->oobsize <= 128 for
+			 * compatibility reasons.
+			 */
+			if (ecc->mode == NAND_ECC_NONE) {
+				mtd_set_ooblayout(mtd,
+						&nand_ooblayout_lp_no_ecc_ops);
+				break;
+			}
+
 			WARN(1, "No oob scheme defined for oobsize %d\n",
 				mtd->oobsize);
 			ret = -EINVAL;
-- 
2.11.0