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SubjectRe: [PATCH] mtd: nand: Add support for reading ooblayout from device tree
On Sat, 12 May 2018 11:38:26 -0300
Paul Cercueil <paul@crapouillou.net> wrote:

> 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.

Indeed. Do you know if there are other kind of layouts in the wild?
Note that <layout-id> can be a string, so if each each board is
defining its own layout, you could specify the board name here.
Otherwise, if you just have those 2 patterns, you can just name them
"contiguous" and "interleaved".


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