mtd nand erase and bad block

[Matteo Facchinetti]

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?


Matteo