Date:	Mon, 18 Apr 2016 16:57:55 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Roger Quadros <rogerq@...com>
Cc:	Tony Lindgren <tony@...mide.com>, <javier@...hile0.org>,
	<fcooper@...com>, <nsekhar@...com>,
	<linux-mtd@...ts.infradead.org>, <linux-omap@...r.kernel.org>,
	<computersforpeace@...il.com>, <dwmw2@...radead.org>,
	<ezequiel@...guardiasur.com.ar>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 00/17] memory: omap-gpmc: mtd: nand: Support GPMC
 NAND on non-OMAP platforms

On Mon, 18 Apr 2016 17:39:01 +0300
Roger Quadros <rogerq@...com> wrote:

> On 18/04/16 17:10, Boris Brezillon wrote:
> > On Mon, 18 Apr 2016 16:48:26 +0300
> > Roger Quadros <rogerq@...com> wrote:
> > 
> >> Boris,
> >>
> >> On 18/04/16 16:13, Boris Brezillon wrote:
> >>> Hi Roger,
> >>>
> >>> On Mon, 18 Apr 2016 15:52:58 +0300
> >>> Roger Quadros <rogerq@...com> wrote:
> >>>
> >>>> On 18/04/16 15:31, Roger Quadros wrote:
> >>>>> On 16/04/16 11:57, Boris Brezillon wrote:
> >>>>>> On Fri, 15 Apr 2016 09:19:51 -0700
> >>>>>> Tony Lindgren <tony@...mide.com> wrote:
> >>>>>>
> >>>>>>>
> >>>>>>>> Or should I just pull this immutable branch in my current nand/next and
> >>>>>>>> let you pull the same immutable branch in omap-soc. I mean, would this
> >>>>>>>> prevent conflicts when our branches are merged into linux-next, no
> >>>>>>>> matter the order.
> >>>>>>>
> >>>>>>> Ideally just one or more branches with just minimal changes in
> >>>>>>> them against -rc1. But you may have other dependencies in
> >>>>>>> your NAND tree so that may no longer be doable :) Usually if
> >>>>>>> I merge something that may need to get merged into other
> >>>>>>> branches, I just apply them into a separate branch against -rc1
> >>>>>>> to start with, then merge that branch in.
> >>>>>>
> >>>>>> Okay, in this case, that's pretty much what I did from the beginning,
> >>>>>> except the immutable branch was provided by Roger (based on 4.6-rc1).
> >>>>>> Thanks for this detailed explanation, I'll try to remember that when
> >>>>>> I'll need to provide an immutable branch for another subsystem.
> >>>>>>
> >>>>>> Roger, my request remains, could you check/test my conflict resolution
> >>>>>> (branch nand/next-with-gpmc-rework)?
> >>>>>
> >>>>> I couldn't test that branch yet as nand/next is broken on omap platforms
> >>>>> (at least on dra7-evm).
> >>>>>
> >>>>> The commit where it breaks is:
> >>>>> a662ef4 mtd: nand: omap2: use mtd_ooblayout_xxx() helpers where appropriate
> >>>>>
> >>>>> I'm trying to figure out what went wrong there. Failure log below.
> >>>>
> >>>> OK. I was able to fix it when at commit a662ef4 with the below patch.
> >>>
> >>> Thanks for debugging that.
> >>>
> >>>>
> >>>> Looks like we need to read exactly the ECC bytes through the ECC engine and not
> >>>> the entire OOB region.
> >>>
> >>> Hm, it looks like there's a bug somewhere else, because I don't see any
> >>> reason why the controller wouldn't be able to read the full OOB region.
> >>
> >> The controller can read the full OOB region but we only want it to read just
> >> the ECC bytes because that is the way the ELM ECC engine works.
> > 
> > Ok, I think I got it: the ECC correction is pipelined with data read,
> > and the controller expect to have ECC bytes right after the in-band
> > data, is that correct?
> 
> That is correct.
> 
> > 
> >>
> >>>>
> >>>> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
> >>>> index e622a1b..46b61d2 100644
> >>>> --- a/drivers/mtd/nand/omap2.c
> >>>> +++ b/drivers/mtd/nand/omap2.c
> >>>> @@ -1547,8 +1547,8 @@ static int omap_read_page_bch(struct mtd_info *mtd, struct nand_chip *chip,
> >>>>  	chip->read_buf(mtd, buf, mtd->writesize);
> >>>>  
> >>>>  	/* Read oob bytes */
> >>>> -	chip->cmdfunc(mtd, NAND_CMD_RNDOUT, mtd->writesize, -1);
> >>>> -	chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
> >>>> +	chip->cmdfunc(mtd, NAND_CMD_RNDOUT, mtd->writesize + chip->ecc.layout->eccpos[0], -1);
> >>>
> >>> The whole point of this series is to get rid of chip->ecc.layout, so
> >>> we'd rather use the mtd_ooblayout_find_eccregion() instead of
> >>> chip->ecc.layout->eccpos[0].
> >>
> >> We just need the position of the first ECC byte offset.
> >> Is that the most optimal way to get it?
> > 
> > For the BCH case, it seems that ECC bytes always start at offset
> > BADBLOCK_MARKER_LENGTH, so you can just pass
> > mtd->writesize + BADBLOCK_MARKER_LENGTH.
> > 
> > Let me know if this works, and I'll squash those changes into the
> > faulty commit (I know this implies a rebase + push -f, but IMO that's
> > better than breaking bisectability).
> > 
> > 
> 
> So, the below patch works as well. Please feel free to fold it with your patch.

Will do.

Thanks,

Boris

> 
> --
> cheers,
> -roger
> 
> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
> index e622a1b..eb85d6b 100644
> --- a/drivers/mtd/nand/omap2.c
> +++ b/drivers/mtd/nand/omap2.c
> @@ -1547,8 +1547,8 @@ static int omap_read_page_bch(struct mtd_info *mtd, struct nand_chip *chip,
>  	chip->read_buf(mtd, buf, mtd->writesize);
>  
>  	/* Read oob bytes */
> -	chip->cmdfunc(mtd, NAND_CMD_RNDOUT, mtd->writesize, -1);
> -	chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
> +	chip->cmdfunc(mtd, NAND_CMD_RNDOUT, mtd->writesize + BADBLOCK_MARKER_LENGTH, -1);
> +	chip->read_buf(mtd, chip->oob_poi, chip->ecc.total);
>  
>  	/* Calculate ecc bytes */
>  	chip->ecc.calculate(mtd, buf, ecc_calc);



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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