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Date: Wed, 07 Sep 2005 20:44:55 +0900
From: Kyungmin Park <kyungmin.park@samsung.com>
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To: 'Bernhard Priewasser' <priewasser@gmail.com>
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Cc: linux-mtd@lists.infradead.org
Subject: RE: [PATCH] OneNAND: Simple Bad Block handling support
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> 
> Kyungmin, I'm still not completely clear about your bad block 
> handling, 
> sorry for bothering you another time.
> 
> In onenand_scan() you call scan_bbt() which calls 
> onenand_memory_bbt() 
>   which calls create_bbt() which builds the BBT using OOB data.
> Fine so far.
> 
> But: the only time onenand_block_checkbad() is called is in 
> onenand_erase() before issueing the (erase-)command to 
> prevent erasing 
> already scanned bad blocks.
> 
> Question: what about reading and writing (onenand_write_ecc(), 
> onenand_read_ecc())? There is no onenand_block_checkbad() before 
> issueing the write/read command. Shouldn't this be done??
> scan_bbt() is only called on initial scan, e.g. device boot. What if 
> this happens very rarely and bad blocks due to wear occur; that meant 
> you cannot provide data integrity.
> 
> I wonder why this is not done in nand_base.c too. I'm afraid I missed 
> some BBT stuff to gather in my investigations :-)... So please kindly 
> excuse me if I'm wrong with my very limited MTD/OneNAND experience!
> 

Yes, The bbt scheme is same as NAND does. and OneNAND bbt is subset of NAND
bbt.
IMHO, There's some historical reason. If I was worng. please correct it
MTD only provides basic operations and handles initial badblock.
The rest is the part of FTL or Filesystem. Is it right?

Regards,

Kyungmin Park