linux-kernel - [PATCH v2 1/3] mtd: rawnand: sunxi: Update OOB layout to match hardware

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Message-Id: <20230204143520.9682-2-samuel@sholland.org>
Date:   Sat,  4 Feb 2023 08:35:18 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>
Cc:     Boris Brezillon <bbrezillon@...nel.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: [PATCH v2 1/3] mtd: rawnand: sunxi: Update OOB layout to match hardware

When using the hardware ECC engine, the OOB data is made available in
the NFC_REG_USER_DATA registers, as one 32-bit word per ECC step. Any
additional bytes are only accessible through raw reads and software
descrambling. For efficiency, and to match the vendor driver, ignore
these extra bytes when using hardware ECC.

Note that until commit 34569d869532 ("mtd: rawnand: sunxi: Fix the size
of the last OOB region"), this extra free area was reported with length
zero, so this is not a functional change for any stable kernel user.

Signed-off-by: Samuel Holland <samuel@...lland.org>
---

Changes in v2:
 - Update commit message to address backward-compatibility concerns

 drivers/mtd/nand/raw/sunxi_nand.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index e673ac46f2e8..3c32d31f20aa 100644
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -1604,6 +1604,13 @@ static int sunxi_nand_ooblayout_free(struct mtd_info *mtd, int section,
 		return 0;
 	}
 
+	/*
+	 * The controller does not provide access to OOB bytes
+	 * past the end of the ECC data.
+	 */
+	if (section == ecc->steps && ecc->engine_type == NAND_ECC_ENGINE_TYPE_ON_HOST)
+		return -ERANGE;
+
 	oobregion->offset = section * (ecc->bytes + 4);
 
 	if (section < ecc->steps)
-- 
2.37.4