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

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

[Karl Beldan]

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")

Signed-off-by: Karl Beldan <kbeldan@baylibre.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 */
-- 
2.9.2

Re: [PATCH] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

[Boris Brezillon]

On Mon, 29 Aug 2016 07:45:49 +0000
Karl Beldan <kbeldan@baylibre.com> wrote:

> 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")
> 
> Signed-off-by: Karl Beldan <kbeldan@baylibre.com>

Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>

Brian, can you take this patch directly in your tree. If that's not
possible, let me know, I'll add the Fixes and Cc:stable tags and take
it for 4.9.

Thanks,

Boris

> ---
>  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 */

Re: [PATCH] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

[Brian Norris]

On Mon, Aug 29, 2016 at 11:59:30AM +0200, Boris Brezillon wrote:
> On Mon, 29 Aug 2016 07:45:49 +0000
> Karl Beldan <kbeldan@baylibre.com> wrote:
> 
> > 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")
> > 
> > Signed-off-by: Karl Beldan <kbeldan@baylibre.com>
> 
> Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> 
> Brian, can you take this patch directly in your tree. If that's not
> possible, let me know, I'll add the Fixes and Cc:stable tags and take
> it for 4.9.

Would this be correct?

Fixes: 6a4123e581b3 ("mtd: nand: davinci_nand, 4-bit ECC for smallpage")

Brian

Re: [PATCH] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

[Boris Brezillon]

On Mon, 29 Aug 2016 13:38:47 -0700
Brian Norris <computersforpeace@gmail.com> wrote:

> On Mon, Aug 29, 2016 at 11:59:30AM +0200, Boris Brezillon wrote:
> > On Mon, 29 Aug 2016 07:45:49 +0000
> > Karl Beldan <kbeldan@baylibre.com> wrote:
> >   
> > > 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")
> > > 
> > > Signed-off-by: Karl Beldan <kbeldan@baylibre.com>  
> > 
> > Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > 
> > Brian, can you take this patch directly in your tree. If that's not
> > possible, let me know, I'll add the Fixes and Cc:stable tags and take
> > it for 4.9.  
> 
> Would this be correct?
> 
> Fixes: 6a4123e581b3 ("mtd: nand: davinci_nand, 4-bit ECC for smallpage")

I'd say so. At least this is where nand_davinci_hwctl_4bit() was
introduced, and it did not contain this 'reset' step.

> 
> Brian

Re: [PATCH] mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl

[Brian Norris]

On Mon, Aug 29, 2016 at 10:45:41PM +0200, Boris Brezillon wrote:
> On Mon, 29 Aug 2016 13:38:47 -0700
> Brian Norris <computersforpeace@gmail.com> wrote:
> 
> > On Mon, Aug 29, 2016 at 11:59:30AM +0200, Boris Brezillon wrote:
> > > Brian, can you take this patch directly in your tree. If that's not
> > > possible, let me know, I'll add the Fixes and Cc:stable tags and take
> > > it for 4.9.  
> > 
> > Would this be correct?
> > 
> > Fixes: 6a4123e581b3 ("mtd: nand: davinci_nand, 4-bit ECC for smallpage")
> 
> I'd say so. At least this is where nand_davinci_hwctl_4bit() was
> introduced, and it did not contain this 'reset' step.

Sorry, didn't notice your reply until now. Very busy... (more about that
later)

Applied to linux-mtd.git, with the Fixes and stable tags.