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

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Date:	Wed, 10 Aug 2016 17:23:23 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Karl Beldan <kbeldan@...libre.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 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.

I will take a look at other patches in this series.

Regards,
Sekhar