[PATCH v7 1/6] mtd: nand: omap: combine different flavours of 1-bit hamming ecc schemes

[Gupta, Pekon]

Dear MTD Maintainers,

> >
> > If I have my NAND formatted with one of the existing ECC schemes (e.g.
> > OMAP_ECC_HAMMING_CODE_DEFAULT) will it work with the new
> > OMAP_ECC_HAM1_CODE_HW scheme?
> >
> > Are they all compatible?
> >
> Yes, they all are 1-bit hamming code, the only difference between
> xx_Default and xx_HW was who was doing the ECC calculation.
> For xx_DEFAULT: ECC calculation was done on CPU via s/w library
> For xx_HW: ECC calculation was done by in-build h/w engine.
> So, all HAMMING_xx can be replaced by HAM1_HW.
> 
> [snip]
> 
> > > @@ -1342,9 +1342,7 @@ static void __maybe_unused
> > gpmc_read_timings_dt(struct device_node *np,
> > >  #ifdef CONFIG_MTD_NAND
> > >
> > >  static const char * const nand_ecc_opts[] = {
> > > -	[OMAP_ECC_HAMMING_CODE_DEFAULT]		= "sw",
> > > -	[OMAP_ECC_HAMMING_CODE_HW]		= "hw",
> > > -	[OMAP_ECC_HAMMING_CODE_HW_ROMCODE]	= "hw-
> > romcode",
> > > +	[OMAP_ECC_HAM1_CODE_HW]			= "ham1",
> > >  	[OMAP_ECC_BCH4_CODE_HW]			= "bch4",
> > >  	[OMAP_ECC_BCH8_CODE_HW]			= "bch8",
> >
> > Won't this break existing dts which have "sw", "hw", or "hw-romcode"?
> >
> > Someone may try to use a new kernel with an old dt, and we marked them
> > as deprecated, not removed.
> >
> HAMMING_xx ECC scheme was used only on legacy platforms, when
> BCH8 was not available, I have not seen anyone using this scheme
> *from mainline kernel* from quite a long time. So, it's safe to remove them.
> 
> This is what was concluded as per below email.
> http://lists.infradead.org/pipermail/linux-mtd/2013-September/048876.html
> 

This patch-series and its follow-on series has already missed many merge
windows, And the above discussion has reached a stalled state (infinite loop)
where, I cannot revert some DT binding updates to and fro to keep all legacy
DT bindings backward compatible forever.
However, I can assure that these DT updates make binding stable for long-term.

So now it's your discretion to whether to accept or leave following 2 series:

http://lists.infradead.org/pipermail/linux-mtd/2013-October/048983.html

http://lists.infradead.org/pipermail/linux-mtd/2013-October/049008.html


AFAIK no-one is using Hamming based ecc-scheme on OMAP platforms
*from mainline kernel*. So this DT update actually does not affect users
I know of. Rather these patch series was intended for long term scalability
and clean-up so that more OMAP users migrate to mainline kernel easily.


with regards, pekon