Re: state of support for "external ECC hardware"

[Gerlando Falauto <gerlando.falauto@keymile.com>]

Hi Ivan,

thanks once more.
Speaking of compatibility, I was wondering: doesn't a NAND flash have 
*any* spare storage space at all, where software could store some 
information about the current OOB layout and/or ECC mechanism?
Partition tables on hard drives for instance have a "partition type" 
byte which provides some hints about what to expect from the data within 
a partition.

This would be especially useful for *future* compatibility (i.e. old 
software reading a NAND "formatted" with unknown mechanism could simply 
stop working, or force read-only mode disabling ECC altogether).

Feasibility aside, would that make any sense?

Thank you,
Gerlando

On 11/12/2012 07:52 PM, Ivan Djelic wrote:
> On Mon, Nov 12, 2012 at 05:39:45PM +0000, Gerlando Falauto wrote:
>> Hi Ivan,
>>
>> wonderful, thanks a lot!
>> If you also happen to have an opionion to using it for chips only
>> needing 1-bit correction, I'd love to hear that...
>
> I would recommend using the strongest ECC your hardware can provide without
> hurting performance too much. This is what I do on my hardware (e.g. 8-bit
> correction on current 4-bit devices). I find it has 2 advantages:
> - increased reliability
> - seamless transition to newer devices with stronger ecc requirements
> The latter is important, because changing ECC strength can be painful: it
> means changing the OOB layout, impacting bootloader and kernel, thus breaking
> compatibility, etc.
> HTH,
> --
> Ivan