mtd nand erase and bad block

[Adrian Hunter]

On 31/05/12 17:28, Matteo Facchinetti wrote:
> On 05/31/2012 03:28 PM, Adrian Hunter wrote:
>> On 31/05/12 15:12, Matteo Facchinetti wrote:
>>> Hi,
>>>
>>> I'm developing a mtd driver for a nand flash controller and I need help;
>>> I'm to the end of the work, and I have problems and dubts about bad block
>>> handling.
>>>
>>> For test, I mark manually bad block byte on flash block.
>>> When I erase with flash_erase, all works and skip the bad block:
>>> :~# flash_erase /dev/mtd6 0 0
>>> Erasing 1024 Kibyte @ 100000 --  2 % complete flash_erase: Skipping bad
>>> block at 00200000
>>> Erasing 1024 Kibyte @ 2700000 -- 100 % complete
>>>
>>> If I try to erase with -N parameter I read the following output:
>>> ~# flash_erase -N /dev/mtd6 0 0
>>> Erasing 1024 Kibnand_erase_nand: attempt to erase a bad block at page
>>> 0x00001600
>>> yte @ 200000 --  5 % complete libmtd: error!: MEMERASE64 ioctl failed for
>>> eraseblock 2 (mtd6)
>>>          error 5 (Input/output error)
>>> flash_erase: error!: /dev/mtd6: MTD Erase failure
>>>               error 5 (Input/output error)
>>> Erasing 1024 Kibyte @ 2700000 -- 100 % complete
>>>
>>> I espected that with -N option, flash_erase should erase the hand-damaged
>>> block, recovering the usability of the block. Is it true?
>>>
>>> What's going wrong?
>>
>> The NAND driver has validation to prevent erasure of bad blocks.  Refer
>> nand_erase_nand() in drivers/mtd/nand/nand_base
>>
>>         /* Check if we have a bad block, we do not erase bad blocks! */
>>         if (nand_block_checkbad(mtd, ((loff_t) page)<<
>>                     chip->page_shift, 0, allowbbt)) {
>>             pr_warn("%s: attempt to erase a bad block at page 0x%08x\n",
>>                     __func__, page);
>>             instr->state = MTD_ERASE_FAILED;
>>             goto erase_exit;
>>         }
>>
>>
> this means that -N parameter bypass only the BBT table check, but in the
> erase routine there is a low level check that forbids the bad block erase.
> 
> What's the way for recheck bad blocks and refresh the BBT from userspace
> application?

I always just temporarily hack the kernel driver to allow the erase of the
bad block in question.