Re: [PATCH V4 2/3] mtd: nand: Calculate better default ecc layout

[Troy Kisky <troy.kisky@boundarydevices.com>]

David Brownell wrote:
> On Friday 26 June 2009, Troy Kisky wrote:
>> Looking through the code, I can only see that
>> Davinci is effected this way when using 512 bytes
>> x 4 steps with hardware ecc.
> 
> You mean, with *single-bit* hardware ECC.

Yes. I do.

> 
> Currently each step needs just three bytes,
> but it's using the default ECC layout which
> allocates six bytes per step.
> 
> 
>> It has its ecc 
>> bytes moved from oob 40-63 to oob 52-63.
> 
> More correctly:  40-42, 46-48, 52-54, 58-60
> to 52-63.

No. More correctly,
40-42  -> 52-54
43-45  -> 55-57
46-48  -> 58-60
49-51  -> 61-63
52-63  -> free space 40-51

> 
> 
>> So a Davinci authority will need to ack this,
>> or request a change.
> 
> Actually I'd just stick with the standard policy
> and not make such an incompatible change in the
> first place.  You can't guarantee that the change
> won't cause regressions...
> 
> It would have been nice if the MTD layer were
> doing this ECC layout before, but in this specific
> case I can't say I think an extra 12 bytes of OOB
> data will matter to anyone.

That was only a side benefit, not the main reason for the patch.

> 
> - Dave


I am perfectly willing to add platform data to the current
evm's to maintain current behavior. As for regressions, could
the next tree help find these?? I have looked fairly closely,
but I definitely could have missed something.


I thank you very much for taking the time to comment upon this.
I'd much rather have a nak than silence.


If anyone ever wants me to post an updated version of the patch
give me a shout. Otherwise, I won't waste anymore of the lists time.


Thanks
Troy