Re: [PATCH v6 00/17] memory: omap-gpmc: mtd: nand: Support GPMC NAND on non-OMAP platforms

[Boris Brezillon]

On Tue, 19 Apr 2016 15:46:19 +0300
Roger Quadros <rogerq@xxxxxx> wrote:

> Boris,
> 
> On 18/04/16 17:57, Boris Brezillon wrote:
> > On Mon, 18 Apr 2016 17:39:01 +0300
> > Roger Quadros <rogerq@xxxxxx> wrote:
> > 
> >> On 18/04/16 17:10, Boris Brezillon wrote:
> >>> On Mon, 18 Apr 2016 16:48:26 +0300
> >>> Roger Quadros <rogerq@xxxxxx> 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@xxxxxx> 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@xxxxxxxxxxx> 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
> 
> After all the changes we discussed in [1] I was able to test nand/next-with-gpmc-rework
> and it worked fine.
> 
> [1] - http://thread.gmane.org/gmane.comp.hardware.netbook.arm.sunxi/22596/focus=22936
> 
> I'd be happy to test the branch again after you've incorporated all changes.
> 
> Since you are gong to do a push -f anyways, I was wondering if you want to pull in my
> gpmc branch first to avoid the merge conflict. But it is totally up to you.

Sure, I can do that.

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