linux-kernel - Re: [PATCH] mtd: nand: Add support for reading ooblayout from device tree

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Date:   Sat, 12 May 2018 15:42:23 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Mark Rutland <mark.rutland@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-mtd@...ts.infradead.org, Rob Herring <robh+dt@...nel.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        Boris Brezillon <boris.brezillon@...in.com>,
        Marek Vasut <marek.vasut@...il.com>
Subject: Re: [PATCH] mtd: nand: Add support for reading ooblayout from
 device tree

On Sat, 12 May 2018 08:55:40 -0300
Paul Cercueil <paul@...pouillou.net> wrote:

> Hi Boris,
> 
> Le 12 mai 2018 02:55, Boris Brezillon <boris.brezillon@...tlin.com> a écrit :
> >
> > Hi Paul, 
> >
> > On Fri, 11 May 2018 23:29:12 +0200 
> > Paul Cercueil <paul@...pouillou.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.

> 
> 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.