[NAND flash driver] What would mtd do if read returns -EBADMSG (ecc failed)

[Du Zhongdong]

On Tue, Oct 21, 2008 at 3:09 PM, Artem Bityutskiy
<dedekind at infradead.org> wrote:
> On Tue, 2008-10-21 at 14:51 +0800, Du Zhongdong wrote:
>> I got another question: if, in my nand flash driver, there's an ECC
>> error cannot be corrected during a read procedure, I think now the
>> block should be marked as a bad block
>
> Read errors do not indicate that the block became bad. For example, if
> you write twice (and different data) to the same NAND page, you'll
> probably end up with ECC errors. But the block will not be bad.
>
> For example, a silly user wrote something to /dev/mtd several times. And
> you have many read errors. Is whole /dev/mtd bad? No, it does not.
>
>> , then two options:
>> 1, I mark that block BAD in my nand flash driver(specifically, I would
>> insert some code in the nand_read() function in nand_base.c to handle
>> this error);
>
> Current model is so that MTD driver is not intelligent. It just reads,
> writes, erases, etc when it is asked to. All bad block management is
> done in upper layers. So this is not your driver's pain.
>
>> 2, I return some error msg the upper layer(ie. MTD layer), which is
>> what nand_read() do at present. Then I would expect the MTD layer
>> would mark that block BAD.
>
> Not the MTD layer, but stuff like UBI or JFFS2 - the _client_ of the MTD
> layer.
>
>> I read s3c2410.c and find that it chose option 2. But I can't find the
>> place in the code where  the MTD layer mark that block BAD.
>
> Right. MTD layer does not do this. It is stupid, and marks blocks as bad
> only when someone calls mtd->block_markbad().
>
> Think about MTD as the very low layer, which just provides the interface
> to work with raw flash chip. Nothing else, no intelligence.
>
> --
> Best regards,
> Artem Bityutskiy (Битюцкий Артём)
>
>

Got it, really appreciate your help

Best regards,
Du Zhongdong