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Date: Sat, 12 May 2018 17:00:34 +0200
From: Boris Brezillon <boris.brezillon@bootlin.com>
To: Paul Cercueil <paul@crapouillou.net>
Cc: Mark Rutland <mark.rutland@arm.com>, David Woodhouse
 <dwmw2@infradead.org>, linux-mtd@lists.infradead.org, Rob Herring
 <robh+dt@kernel.org>, linux-kernel@vger.kernel.org,
 devicetree@vger.kernel.org, Brian Norris <computersforpeace@gmail.com>,
 Richard Weinberger <richard@nod.at>, Boris Brezillon
 <boris.brezillon@bolin.com>, Marek Vasut <marek.vasut@gmail.com>
Subject: Re: [PATCH] mtd: nand: Add support for reading ooblayout from
 device tree
Message-ID: <20180512170034.12779313@bbrezillon>
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On Sat, 12 May 2018 11:38:26 -0300
Paul Cercueil <paul@crapouillou.net> wrote:

> Le sam. 12 mai 2018 =C3=A0 10:42, Boris Brezillon=20
> <boris.brezillon@bootlin.com> a =C3=A9crit :
> > On Sat, 12 May 2018 08:55:40 -0300
> > Paul Cercueil <paul@crapouillou.net> wrote:
> >  =20
> >>  Hi Boris,
> >>=20
> >>  Le 12 mai 2018 02:55, Boris Brezillon <boris.brezillon@bootlin.com>=20
> >> a =C3=A9crit : =20
> >>  >
> >>  > Hi Paul,
> >>  >
> >>  > On Fri, 11 May 2018 23:29:12 +0200
> >>  > Paul Cercueil <paul@crapouillou.net> wrote:
> >>  > =20
> >>  > > By specifying the properties "mtd-oob-ecc" and "mtd-oob-free",  =
=20
> >> it is =20
> >>  > > now possible to specify from devicetree where the ECC data is  =20
> >> located =20
> >>  > > inside the OOB region. =20
> >>  >
> >>  > Why would we want to do that? I mean, ECC/free regions are ECC
> >>  > controller dependent (and NAND chip dependent for the OOB size  =20
> >> part), =20
> >>  > so there's no reason to describe it in the DT. And more  =20
> >> importantly, =20
> >>  > people are likely to get it wrong.
> >>  >
> >>  > I'm curious, why do you need that? =20
> >>=20
> >>  Good question.
> >>=20
> >>  The reason is that some SoCs have no ECC controller.
> >>  The various boards for these SoCs then all use a different layout. =20
> >=20
> > 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 =3D <layout-id>), but not a generic way to
> > define custom layouts for all kind of NAND controller. =20
>=20
> Okay.
>=20
> >>=20
> >>  My motivation is to get rid of this (move it to devicetree):
> >> =20
> >> 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. =20
> >=20
> > 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. =20
>=20
> 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
>=20
> 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".