[U-Boot] NAND flash - bad blocks

[Dimitar Penev <dpn@switchfin.org>]

Hi Scott,

I have tried to do some more tests on the board with the NAND chip I have 
scrub-ed

-I have done 'nand erase.chip clean' and tried to probe different nand 
regions
(I have 128MB RAM and 1GB NAND and I am not sure how I could dump the whole 
NAND at once)
It seems the whole NAND is 0xFF

After that I have written 10MB at the beginning of the NAND and those data 
was verified to be written OK
Outside of the 10MB region the NAND stays 0xFF

in Linux 'nandtest' doesn't report any issue.

So I tend to think that nand scrub did a good think for me.

Best Regards
Dimitar

----- Original Message ----- 
From: "Scott Wood" <scottwood@freescale.com>
To: "Dimitar Penev" <dpn@switchfin.org>
Cc: <u-boot@lists.denx.de>
Sent: Friday, January 11, 2013 10:21 PM
Subject: Re: [U-Boot] NAND flash - bad blocks


On 01/11/2013 02:46:06 AM, Dimitar Penev wrote:
> Hi Scott,
>
>> On 01/10/2013 01:56:30 AM, Dimitar Penev wrote:
>>> Hello,
>>>
>>> First of all sorry if this question was already answered here.
>>>
>>> We are sourcing some K9F8G08U0M-PIB0 NAND flash devices.
>>> On the first erase in uboot 2011.09 I got bunch of mostly  consecutive 
>>> bad blocks.
>>> According to the datasheet we should get not more then 80 bad  blocks 
>>> for our chip
>>> but I get something like 240 bad blocks for most of the NAND chips.
>>>
>>> I seems to be able to fix this using the following procedure:
>>
>> Call your NAND vendor and complain?
>>
>
> Well we did but we didn't got something from them which could explain 
> what we observe.
>
>> After making sure that there's nothing wrong with your NAND driver  or 
>> controller that causes the OOB to be read incorrectly.
>
> We are using nand_plat driver provide by ADI without any  customization.

Still, do some investigation to see whether it seems to be working.
Dump the raw data that you read -- is it mostly 0xff with some bad
block markers set, or is it returning garbage?  Do any of the blocks
that are not marked bad have non-0xff data?  If you do a scrub of the
entire NAND chip, then write to one block, does the write show up
anywhere else on the NAND chip?

>>> In uboot
>>> uboot>nand scrub.chip
>>>
>>> In uboot
>>> uboot>nand erase.chip clean
>>> at this point I get usually 1,2 bad blocks which looks normal to me.
>>
>> You're not fixing anything -- you're wiping out all bad block 
>> information. Those "1,2 bad blocks" are not actually bad blocks,  but 
>> are the bad block table which appears "bad" to reserve it.   These 
>> should be at the end of flash.  Or, possibly, they're blocks  that 
>> happen to be damaged in a way that prevents the bad block  marker from 
>> becoming 0xff.
>
> Oh Really?
> What about 'nandtest -m' in Linux ? I was hoping it does a check of  the 
> erase blocks.

That's no substitute for having the factory bad block markers.
Nandtest doesn't look very rigorous at all -- and only seems to mark
bad blocks if the erase or write operations return failure, not if it
sees an uncorrectable error on readback.

> Thanks Scott.
> Is there any procedure to analyze the nand flash for bad blocks?

Yes, and it's done by the flash manufacturer to produce bad block
markers. :-P

-Scott