linux-kernel - [PATCH 3.10 209/319] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

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Date:   Sun,  5 Feb 2017 20:20:31 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Karl Beldan <kbeldan@...libre.com>,
        Brian Norris <computersforpeace@...il.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 209/319] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

From: Karl Beldan <kbeldan@...libre.com>

commit f6d7c1b5598b6407c3f1da795dd54acf99c1990c upstream.

This fixes subpage writes when using 4-bit HW ECC.

There has been numerous reports about ECC errors with devices using this
driver for a while.  Also the 4-bit ECC has been reported as broken with
subpages in [1] and with 16 bits NANDs in the driver and in mach* board
files both in mainline and in the vendor BSPs.

What I saw with 4-bit ECC on a 16bits NAND (on an LCDK) which got me to
try reinitializing the ECC engine:
- R/W on whole pages properly generates/checks RS code
- try writing the 1st subpage only of a blank page, the subpage is well
  written and the RS code properly generated, re-reading the same page
  the HW detects some ECC error, reading the same page again no ECC
  error is detected

Note that the ECC engine is already reinitialized in the 1-bit case.

Tested on my LCDK with UBI+UBIFS using subpages.
This could potentially get rid of the issue workarounded in [1].

[1] 28c015a9daab ("mtd: davinci-nand: disable subpage write for keystone-nand")

Fixes: 6a4123e581b3 ("mtd: nand: davinci_nand, 4-bit ECC for smallpage")
Signed-off-by: Karl Beldan <kbeldan@...libre.com>
Acked-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@...il.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 drivers/mtd/nand/davinci_nand.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index c3e15a5..e4f16cf 100644
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -241,6 +241,9 @@ static void nand_davinci_hwctl_4bit(struct mtd_info *mtd, int mode)
 	unsigned long flags;
 	u32 val;
 
+	/* Reset ECC hardware */
+	davinci_nand_readl(info, NAND_4BIT_ECC1_OFFSET);
+
 	spin_lock_irqsave(&davinci_nand_lock, flags);
 
 	/* Start 4-bit ECC calculation for read/write */
-- 
2.8.0.rc2.1.gbe9624a