Way to clear nand bad block table

[Sascha Hauer]

On Fri, Jul 27, 2012 at 11:24:48AM +1000, Marc Reilly wrote:
> Hi Juergen,
> 
> Thanks for your ideas.
> 
> I managed to clear the BBT, it was a bit of a hack... the saga is below for 
> anyone who runs into similar problem.
> 
> On Thursday, July 26, 2012 11:27:48 AM Juergen Beisert wrote:
> > The flash blocks which contains the "bad block table" are protected by
> > the "bad block table" aware MTD layer.
> > 
> > So, the ugly way: run a bootloader which does not use the in-flash bad block
> > table. Then the tables are regular blocks in the flash and can be erased.
> > After that run again the bad block table aware bootloader and it will
> > re-create the in-flash table. But be careful: In this case the generic
> > functions scans all blocks in the NAND to collect the bad block markers in
> > each NAND block's OOB. If this information is already destroyed somehow,
> > this solution does not help.
> 
> Recompiling barebox with bbt support disabled stopped the all the bad block 
> messages, however erasing the nand didn't clear the BBT for subsequent 
> reboots...
> The issue was that the erase commands and functions skip erasing bad blocks, 
> and the blocks that held the actual BBT were being considered bad, so they 
> weren't getting erased. After commenting out calls to nand_block_checkbad() in 
> nand_write.c and block_isbad() in mtd_erase()/core.c I was able to manually 
> erase the blocks. (erasing actual bad blocks results in I/O error)
> Next restart of barebox the BBT was regenerated with the two actual bad 
> blocks.
> 
> After all that, I noticed imx_low_erase() in nand_imx.c. Probably would have 
> been easier to make up a command around that.

This problem comes up regularly. I remember Wolfram implemented a nand
'scrub' command. He was working on i.MX28. I don't know wether his
command was i.MX28 specific, but it would be nice to have such a command
around.

Sascha

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