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

[Paul Cercueil]

Le sam. 12 mai 2018 à 10:42, Boris Brezillon 
<boris.brezillon@xxxxxxxxxxx> a écrit :
> On Sat, 12 May 2018 08:55:40 -0300
> Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
>
> >  Hi Boris,
> >
> >  Le 12 mai 2018 02:55, Boris Brezillon <boris.brezillon@xxxxxxxxxxx> 
> > a écrit :
> >  >
> >  > Hi Paul,
> >  >
> >  > On Fri, 11 May 2018 23:29:12 +0200
> >  > Paul Cercueil <paul@xxxxxxxxxxxxxxx> 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