Re: [PATCH 0/2] Use badblockbits-like approach in nand_bbt.c

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Brian,

On Fri,  6 Mar 2015 13:12:16 +0100
rnd4@dave-tech.it wrote:

> 
> Hi all,
> 
> I'm currenlty working with an MLC NAND (MT29F32G08CBACAWP) on a iMX6 based
> platform (kernel 3.10.17).
> The first problem I have is about badblock detection. I experienced a lot of bit
> flips on badblock marker (some of them probalbly due misuse, e.g. powercut).
> 
> By looking into the MDT code, I've found that inside nand_base.c there's support
> for badblockbits feature, which, for short, allow to tolerate 1 or more bitflip
> when looking for BB.
> 
> In my experience usually the marker is 0x00 for bad blocks and 0xFF for good one
> (at least this is true for my current component).
> 
> Unfortunately this approach is not used into BBT code (nand_bbt.c) and thus I have
> a lot of false positive BB.
> 
> With the following patches I try to add badblockbits-like approach to nand_bbt.c
> code.
> 
> The first patch is optional and configure badblockbits depending on SLC vs MLC NAND.
> 
> The second patch implements the badblockbits approach into BBT scan.
> Please note that this is not usually enough, because many NAND controller override
> nand_bbt_descr and thus requires changes also the the specific controller driver.
> 
> The patch has been made in collaboration with Boris Brezillon (thank you for you
> suggestions Boris).
> 
> I tested it on a 3.10.17 kernel, but the second patch applies fine to
> v3.10 stable and latest 4.0-rc1 (the first patch needs some changes to apply to this
> one).
> 
> Feel free to comment it and tell me if something can be done in a better way

We recently discussed the option of retrieving BBM using raw access
mode, which will likely require something similar to what this series is
doing.
I'm still not happy with the selection of ->badblockbits (4 for MLC
NANDs and 8 otherwise), but maybe that's something we can adjust later.

What do you think?

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com