[RFC] Change ECC algorithm from userspace

[Javier Martinez Canillas]

On Fri, Oct 28, 2011 at 12:30 PM, Matthieu CASTET
<matthieu.castet at parrot.com> wrote:
> Hi,
>
> Javier Martinez Canillas a écrit :
>> Hello,
>>
>> I want to be able to use 1-bit ECC for the first partition where I
>> save the loader binary and has to be accessed by the ROM boot but use
>> a 4-bit ECC for my rootfs partition.
>>
>> Does anyone have this same issue?
> We use raw programming and compute the ecc in software.
>
>

Hi Matthieu,

We also thought that solution but it wasn't clear for me if doing a
RAW write to the mtd device I skip the NAND driver and could also
write the oob section without that value being recalculate and rewrite
by the driver.

>>
>> What is the best approach to store data in a NAND device using
>> different ECC techniques?
>>
>> I've think of two approaches:
>>
>> 1- Adding an ioctl to mtdchar (something like ECCSETBITS) to change
>> the ECC technique used.
> But this won't work if there is concurrent acess to mtd. One program may want 1
> bit ecc other want 4 bits ecc.
>
>> 2- Use a platform data field to notify the omap2 nand driver that the
>> ROM boot only supports 1-bit ECC. So it can use a 1-bit ECC to write
>> and read the first 4 sectors but a 4-bit ECC for the rest.
> This may be better.
>
> Matthieu
>
> PS : note that some OMAP ROM support a better protection than Hamming (but the
> details are not public AFAIK)
>
> From OMAP34xx Multimedia Device, Silicon Revision 3.1.x, public version :
>
> Pages can contain errors caused by memory alteration. To correct these errors,
> the ROM code uses ECC,
> based on Hamming codes for SLC NAND and BCH (Bose, Ray-Chaudhuri, Hocquenghem)
> code for
> multilevel cell (MLC) devices. The computed ECC is compared to ECC stored in the
> spare area of the
> corresponding page. If there are uncorrectable errors, the ROM code returns with
> FAIL.
>

Yes I've read that on the DM3730 TRM but as far as I understand only
applies to MLC devices, but ours is SLC.

Thank you and best regards,

-- 
Javier Martínez Canillas
(+34) 682 39 81 69
Barcelona, Spain