[U-Boot] flash post test

[Scott Wood <scottwood@freescale.com>]

On 02/06/2012 04:59 PM, Albert ARIBAUD wrote:
> Hi Scott,
> 
> Le 06/02/2012 23:55, Scott Wood a ?crit :
>> On 02/06/2012 04:23 PM, Albert ARIBAUD wrote:
>>> Hi Vaibhav,
>>>
>>> Le 06/02/2012 05:57, vaibhav kothari a ?crit :
>>>> hi albert
>>>>
>>>> Yes,actually there is already support of flash test in POST of latest
>>>> uboot.They are testing flash on every power on so am I for my
>>>> board.But i
>>>> don't want to disturb sectors in which uboot code relies. Can you
>>>> help me
>>>> here?
>>>
>>> I am no NAND specialist, but I do hope NAND POST tests are pure read
>>> tests and thus are not affected by poweroffs (and can actually test any
>>> part of NAND).
>>
>> NAND has a property called "read disturb", where excessively reading a
>> sector without writing to it can eventually cause data loss.  U-Boot is
>> already read once per boot, but reading it a second time could halve the
>> expected lifetime.  Data managed by something like ubi is be scrubbed in
>> a way that avoids this, but U-Boot itself is not usually managed in this
>> way (boot hardware/rom does not understand ubi).
> 
> I *did* say I am not a NAND expert. :)
> 
> Thanks Scott. But then, isn't NAND testing a kind of catch-22, where by
> actually tesing if NAND works it one ends up weakening it either through
> read disturb, or simply through writes?

It's fine for occasional manual testing, or routine testing of an area
that gets properly scrubbed.

-Scott