linux-kernel - Re: [PATCH 3/4] ARM: dts: da850-lcdk: Add NAND to DT

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Message-ID: <20160829074958.GA30462@gobelin>
Date:   Mon, 29 Aug 2016 07:49:58 +0000
From:   Karl Beldan <kbeldan@...libre.com>
To:     Sekhar Nori <nsekhar@...com>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Karl Beldan <karl.beldan+oss@...il.com>
Subject: Re: [PATCH 3/4] ARM: dts: da850-lcdk: Add NAND to DT

On Tue, Aug 16, 2016 at 11:20:29PM +0000, Karl Beldan wrote:
> On Wed, Aug 10, 2016 at 05:23:23PM +0530, Sekhar Nori wrote:
> > On Wednesday 10 August 2016 04:49 PM, Karl Beldan wrote:
> > > On Wed, Aug 10, 2016 at 03:01:30PM +0530, Sekhar Nori wrote:
> > >> On Wednesday 10 August 2016 02:34 PM, Karl Beldan wrote:
> > >>> On Wed, Aug 10, 2016 at 02:01:57PM +0530, Sekhar Nori wrote:
> > >>>> On Tuesday 09 August 2016 10:45 PM, Karl Beldan wrote:
> > >>>>> This adds DT support for the NAND connected to the SoC AEMIF.
> > >>>>> The parameters (timings, ecc) are the same as what the board ships with
> > >>>>> (default AEMIF timings, 1bit ECC) and improvements will be handled in
> > >>>>> due course.
> > >>>>
> > >>>> I disagree that we need to be compatible to the software that ships with
> > >>>> the board. Thats software was last updated 3 years ago. Instead I would
> > >>>> concern with what the hardware supports. So, if the hardware can support
> > >>>> 4-bit ECC, I would use that.
> > >>>>
> > >>> I am not saying we _need_ to be compatible.
> > >>
> > >> Alright then, please drop references to what software the board ships
> > >> with in the commit message and in the patch itself.
> > >>
> > > 
> > > I hadn't seen this comment before sending v2.
> > > 
> > >>>
> > >>>> If driver is broken for 4-bit ECC, please fix that up first.
> > >>>>
> > >>> Since this issue is completely separate from my DT improvements
> > >>> I'll stick to resubmitting the series, applying my LCDK changes to the
> > >>> EVM too, besides you'll be able to compare the behavior without ECC
> > >>> discrepancies.
> > >>> I took note that you are likely to not apply without the ECC fix.
> > >>
> > >> Yeah, I would not like to apply with 1-bit ECC now and then change to
> > >> 4-bit ECC soon after.
> > >>
> > > 
> > > Both mityomapl138 from mainline and hawkboard from TI's BSP release
> > > include the comment:
> > > - "4 bit mode is not supported with 16 bit NAND"
> > > It is not clear whether they imply that the HW has issues or if it's SW
> > 
> > At least the TRM says "The EMIFA supports 4-bit ECC on 8-bit/16-bit NAND
> > Flash.". And then the TRM goes on to describe how 4-bit ECC is supposed
> > to work for 16-bit NAND. I could not find any errata related to this in
> > the errata document.
> > 
> > > only, but 4-bits ECC is a different matter and I hope you'll integrate
> > > the current changes prior to tackling it.
> > 
> > Lets apply everything together. This is a new feature, not a bug fix.
> > There is no need to rush it. Also, for the NAND part on LCDK, per the
> > micron datasheet, minimum of 4-bit ECC is needed.
> > 
> 
> FYI my patches are related to a small contracting work spanning 20 days
> amounting to 15 real days (from scratch).  ATM my SoW not only doesn't
> include this 'new feature' but excludes it. So I cannot promise I'll
> look into it, though it shouldn't be too big a thing.

I took a look at it yesterday, cf. https://lkml.org/lkml/2016/8/29/71
 
Karl

> It seemed clear that you wanted to squeeze it with the rest, but after
> setting things up for the EVM and observing mainline was broken with
> 4bits ECC on an 8bits NAND I thought it was impossible nobody hadn't
> noticed it .. so I dug in the mail archive, only to find there had
> already been some alerts raised some months ago on the list, so I picked
> up my next item.
> 
> > I will take a look at other patches in this series.
> > 
> 
> Ok, thanks.
> 
> Rgds, 
> Karl