[PATCH v6 1/4] ARM: OMAP2+: cleaned-up DT support of various ECC schemes

[Gupta, Pekon]

Hi,

> >
> > diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
> b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
> > index df338cb..958e5d5 100644
> > --- a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
> > +++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
> > @@ -21,11 +21,8 @@ Optional properties:
> >                                 is wired that way. If not specified, a bus
> >                                 width of 8 is assumed.
> >
> > - - ti,nand-ecc-opt:            A string setting the ECC layout to use. One of:
> > -
> > -               "sw"            Software method (default)
> > -               "hw"            Hardware method
> > -               "hw-romcode"    gpmc hamming mode method & romcode layout
> > + - ti,nand-ecc-scheme:         A string setting the ECC layout to use. One of:
> > +               "ham1"          1-bit Hamming ecc code
> 
> As has been pointed out, this breaks compatibility which should be
> avoided unless you know the state of use of this binding. I fail to
> see the advantage of using scheme over opt. You could simply add ham1
> here and maintain compatibility. Instead of removing sw, hw, etc. you
> can simply deprecate them or decide that the kernel doesn't support
> those options.
> 
Renaming 'ti,nand-ecc-opt' to 'ti,nand-ecc-scheme' was as per earlier 
comments from Olof. So either way is fine with me. Should I revert
it back to 'ti,nand-ecc-opt' ?

Also, "sw", "hw_romcode" have been deprecated, they are no longer
supported in driver. So shouldn't they be removed from the documentation ?

> However, since you are willing to break compatibility, then you should
> the generic NAND binding and use nand-ecc-mode adding the values you
> need.
> 
> Documentation/devicetree/bindings/mtd/nand.txt:
> * MTD generic binding
> 
> - nand-ecc-mode : String, operation mode of the NAND ecc mode.
>   Supported values are: "none", "soft", "hw", "hw_syndrome",
> "hw_oob_first",
>   "soft_bch".

Yes I can use generic 'nand-ecc-mode', But the binding values like
"soft", "hw", "soft_bch" are too generic to describe the hardware.
- BCH ECC scheme can itself be of multiple types, bch4/bch8/bch16
  so "soft_bch" is ambiguous.
- Similarly "soft" and "hw" do not determine the algorithm used
   like Hamming or BCH.

(a) Should I update the generic binding values (if no one else is using) ? like 
	sw -> ham1_sw
	hw -> ham1_hw
	soft_bch-> soft_bch4, soft_bch8
OR 
(b) Should I add newer ones to it (like "ham1", "bch4", "bch8", "bch16") ?
      keeping the old ones intact. And how should I handle un-supported
     values, (Is pr_err during kernel probe enough ?).

[...]

> > - - elm_id:     Specifies elm device node. This is required to support BCH
> > -               error correction using ELM module.
> > + - ti,elm-id:  Specifies pHandle of the ELM devicetree node.
> > +               ELM is an on-chip hardware engine on TI SoC which is used for
> > +               locating ECC errors for BCHx algorithms. SoC devices which have
> > +               ELM hardware engines should specify this device node in .dtsi
> > +               Using ELM for ECC error correction frees some CPU cycles.
> 
> While yes, this is better name and documentation, I don't know that
> breaking compatibility is justified.
> 
As this is TI specific binding, so manufacturer's name should have been
included.  But as this was missed while adding this binding, so this should
be fixed now. (Olof also recommended the same).

AFAIK, For TI's NAND OMAP driver, currently there are not many
end-users are using these bindings from mainline DT kernel.
So this patch series mainly aims to cleanup NAND driver so that migrate
to latest DT based kernel from board-file one is easy.
So changes should be acceptable from end-user's point, its only matter
of which path to take. 
Request you to please help me finalize this before I resend next patch
series addressing other comments from Brian.

Thank You..
with regards, pekon