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

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Message-ID: <20160829224541.545f622d@bbrezillon>
Date:   Mon, 29 Aug 2016 22:45:41 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Brian Norris <computersforpeace@...il.com>
Cc:     Karl Beldan <kbeldan@...libre.com>, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...libre.com>,
        Karl Beldan <karl.beldan+oss@...il.com>
Subject: Re: [PATCH] mtd: nand: davinci: Reinitialize the HW ECC engine in
 4bit hwctl

On Mon, 29 Aug 2016 13:38:47 -0700
Brian Norris <computersforpeace@...il.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@...libre.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@...libre.com>  
> > 
> > Acked-by: Boris Brezillon <boris.brezillon@...e-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