linux-kernel - [PATCH 2/3] mtd: nand: Support maximizing ECC when using software BCH

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Message-Id: <1465397926-7904-3-git-send-email-boris.brezillon@free-electrons.com>
Date:	Wed,  8 Jun 2016 16:58:45 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-mtd@...ts.infradead.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Richard Weinberger <richard@....at>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] mtd: nand: Support maximizing ECC when using software BCH

Add support for ECC maximization when software BCH with
nand_ooblayout_lp_ops layout is used.
Other cases should be handled by the NAND controller driver.

Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
---
 drivers/mtd/nand/nand_base.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d374129..ca4f53d 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -4224,6 +4224,7 @@ static int nand_set_ecc_soft_ops(struct mtd_info *mtd)
 		ecc->write_page_raw = nand_write_page_raw;
 		ecc->read_oob = nand_read_oob_std;
 		ecc->write_oob = nand_write_oob_std;
+
 		/*
 		* Board driver should supply ecc.size and ecc.strength
 		* values to select how many bits are correctable.
@@ -4246,6 +4247,25 @@ static int nand_set_ecc_soft_ops(struct mtd_info *mtd)
 			}
 
 			mtd_set_ooblayout(mtd, &nand_ooblayout_lp_ops);
+
+		}
+
+		/*
+		 * We can only maximize ECC config when the default layout is
+		 * used, otherwise we don't know how many bytes can really be
+		 * used.
+		 */
+		if (mtd->ooblayout == &nand_ooblayout_lp_ops &&
+		    ecc->options & NAND_ECC_MAXIMIZE) {
+			int steps, bytes;
+
+			/* Always prefer 1k blocks over 512bytes ones */
+			ecc->size = 1024;
+			steps = mtd->writesize / ecc->size;
+
+			/* Reserve 2 bytes for the BBM */
+			bytes = (mtd->oobsize - 2) / steps;
+			ecc->strength = bytes * 8 / fls(8 * ecc->size);
 		}
 
 		/* See nand_bch_init() for details. */
-- 
2.7.4