linux-kernel - [PATCH 1/2] mtd: nand: make Samsung SLC NAND usable again

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Date:   Tue, 29 Aug 2017 12:17:12 +0200
From:   Lothar Waßmann <LW@...O-electronics.de>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Brian Norris <computersforpeace@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        David Woodhouse <dwmw2@...radead.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Cc:     Lothar Waßmann <LW@...O-electronics.de>
Subject: [PATCH 1/2] mtd: nand: make Samsung SLC NAND usable again

commit c51d0ac59f24 ("mtd: nand: Move Samsung specific init/detection
logic in nand_samsung.c") introduced a regression for Samsung SLC NAND
chips. Prior to this commit chip->bits_per_cell was initialized by calling
nand_get_bits_per_cell() before using nand_is_slc().
With the offending commit this call is skipped, leaving
chip->bits_per_cell cleared to zero when the manufacturer specific
'.detect' function calls nand_is_slc() which in turn interprets
bits_per_cell != 1 as indication for an MLC chip.
The effect is that e.g. a K9F1G08U0F NAND chip is falsely detected as
MLC NAND with 4KiB page size rather than SLC with 2KiB page size.

Add a call to nand_get_bits_per_cell() before calling the .detect hook
function in nand_manufacturer_detect(), so that the nand_is_slc()
calls in the manufacturer specific code will return correct results.

Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
---
 drivers/mtd/nand/nand_base.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 9900476..bcc8cef1 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -3820,10 +3820,13 @@ static void nand_manufacturer_detect(struct nand_chip *chip)
 	 * nand_decode_ext_id() otherwise.
 	 */
 	if (chip->manufacturer.desc && chip->manufacturer.desc->ops &&
-	    chip->manufacturer.desc->ops->detect)
+	    chip->manufacturer.desc->ops->detect) {
+		/* The 3rd id byte holds MLC / multichip data */
+		chip->bits_per_cell = nand_get_bits_per_cell(chip->id.data[2]);
 		chip->manufacturer.desc->ops->detect(chip);
-	else
+	} else {
 		nand_decode_ext_id(chip);
+	}
 }

 /*
-- 
2.1.4