[U-Boot] NAND Bad Blocks and OOB

[U-Boot] NAND Bad Blocks and OOB

[VirtualFight at web.de]

Hi all,
I have some questions about the bad block management in the NAND-driver, I hope this is the right place to ask this:

The things I believe to know, please correct me, if its wrong:
If
 I have a new NAND-Flash, the manufacturer marked the bad block in the 
spare area/OOB  (normaly good blocks are marked as 0xFF in the first 2 
bytes?).
The u-boot scans for these bad blocks and saves the information in the bbt.

What
 happens, if a block gets worn out? Would this block only be markes as 
bad in the bbt, or would this information would be also stored in the 
spare area (the driver write another value, not  0xFF in the firts 2 
bytes?).
Is it possible to restore the bad block informations, if the
 whole nand-flash would be erased (for example by writing 0 in all block
 and after this by erasing the blocks and check the error status bit of 
the NAND-flash device)?
If yes, is such a function implemented in u-boot?

thanks in advance,
marc
 

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[U-Boot] NAND Bad Blocks and OOB

[Scott Wood]

On Fri, 18 Mar 2011 12:43:06 +0100
<VirtualFight@web.de> wrote:

> 
> Hi all,
> I have some questions about the bad block management in the NAND-driver, I hope this is the right place to ask this:
> 
> The things I believe to know, please correct me, if its wrong:
> If
>  I have a new NAND-Flash, the manufacturer marked the bad block in the 
> spare area/OOB  (normaly good blocks are marked as 0xFF in the first 2 
> bytes?).
> The u-boot scans for these bad blocks and saves the information in the bbt.
> 
> What
>  happens, if a block gets worn out? Would this block only be markes as 
> bad in the bbt, or would this information would be also stored in the 
> spare area (the driver write another value, not  0xFF in the firts 2 
> bytes?).

As long as you have an in-flash bbt, it only gets marked in the bbt.  If you
don't have an in-flash bbt, an OOB bad block marker is written.

> Is it possible to restore the bad block informations, if the
>  whole nand-flash would be erased (for example by writing 0 in all block
>  and after this by erasing the blocks and check the error status bit of 
> the NAND-flash device)?

It's possible to do your own testing and mark blocks bad as a result, but
you're not really restoring the original information.  The manufacturer may
have used a more rigorous test.

> If yes, is such a function implemented in u-boot?

No.  You should avoid clearing manufacturer-set bad block markers.

-Scott