mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=f6d7c1b5598b6407c3f1da795dd54acf99c1990c
Commit:     f6d7c1b5598b6407c3f1da795dd54acf99c1990c
Parent:     a93295a7e118b5c58391906e47183775b1eb7cb1
Author:     Karl Beldan <kbeldan at baylibre.com>
AuthorDate: Mon Aug 29 07:45:49 2016 +0000
Committer:  Brian Norris <computersforpeace at gmail.com>
CommitDate: Fri Sep 9 19:39:33 2016 -0700

    mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl
    
    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")
    Cc: <stable at vger.kernel.org>
    Signed-off-by: Karl Beldan <kbeldan at baylibre.com>
    Acked-by: Boris Brezillon <boris.brezillon at free-electrons.com>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
 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 cc07ba0..27fa8b8 100644
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -240,6 +240,9 @@ 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 */