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Date: Sat, 12 May 2018 11:38:26 -0300
From: Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH] mtd: nand: Add support for reading ooblayout from device
 tree
To: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
        David Woodhouse <dwmw2@infradead.org>, linux-mtd@lists.infradead.org,
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Le sam. 12 mai 2018 à 10:42, Boris Brezillon 
<boris.brezillon@bootlin.com> a écrit :
> On Sat, 12 May 2018 08:55:40 -0300
> Paul Cercueil <paul@crapouillou.net> wrote:
> 
>>  Hi Boris,
>> 
>>  Le 12 mai 2018 02:55, Boris Brezillon <boris.brezillon@bootlin.com> 
>> a écrit :
>>  >
>>  > Hi Paul,
>>  >
>>  > On Fri, 11 May 2018 23:29:12 +0200
>>  > Paul Cercueil <paul@crapouillou.net> wrote:
>>  >
>>  > > By specifying the properties "mtd-oob-ecc" and "mtd-oob-free", 
>> it is
>>  > > now possible to specify from devicetree where the ECC data is 
>> located
>>  > > inside the OOB region.
>>  >
>>  > Why would we want to do that? I mean, ECC/free regions are ECC
>>  > controller dependent (and NAND chip dependent for the OOB size 
>> part),
>>  > so there's no reason to describe it in the DT. And more 
>> importantly,
>>  > people are likely to get it wrong.
>>  >
>>  > I'm curious, why do you need that?
>> 
>>  Good question.
>> 
>>  The reason is that some SoCs have no ECC controller.
>>  The various boards for these SoCs then all use a different layout.
> 
> Okay. Still think defining the layouts in the DT is a bad idea. We
> can add a jz4740 specific property to define the layout id
> (ingenic,nand-oob-layout = <layout-id>), but not a generic way to
> define custom layouts for all kind of NAND controller.

Okay.

>> 
>>  My motivation is to get rid of this (move it to devicetree):
>>  
>> https://elixir.bootlin.com/linux/latest/source/arch/mips/jz4740/board-qi_lb60.c#L93
>>  And enable the support of other boards with custom OOB layouts.
> 
> Can you list the different layouts you have? I'm pretty sure there's a
> pattern. Maybe we can even deduce the layout from the page size or OOB
> size.

This is the other layout I have for another ingenic device:
http://projects.qi-hardware.com/index.php/p/qi-kernel/source/tree/od-2011-09-18/arch/mips/jz4740/board-a320.c#L125

Page size and OOB size are the same between these two devices.

-Paul