Bad Block management routine for MTD NandFlash driver?

Bad Block management routine for MTD NandFlash driver?

[Jason Chan]

Hi all,
    Any bad block management routine (eg. Invalid block table ) is 
implemented for MTD NandFlash driver?
It seems that the ECC routine is not enough for my nandflash driver. And 
I need a more robust bad block management routine for that. Should I 
implement the invalid block table by myself, or there are some already 
implemented?

-- 
Best Regards,

Jason Chan
Emsoft Ltd.

Re: Bad Block management routine for MTD NandFlash driver?

[David Woodhouse]

jason@emsoftltd.com said:
>     Any bad block management routine (eg. Invalid block table ) is
> implemented for MTD NandFlash driver? It seems that the ECC routine is
> not enough for my nandflash driver. And  I need a more robust bad
> block management routine for that.

The low-level hardware driver does not implement and bad block management. 
That is done by whatever file system or translation layer you use on the 
flash. What are you intending to use? JFFS2?

--
dwmw2

Re: Bad Block management routine for MTD NandFlash driver?

[Jason Chan]

David,
    I trying to use EXT2 for my nandflash driver. Is that OK?

When I make a EXT2 file system on the nandflash driver, the 
mtd/nand/nand.c show a error message that "nand_erase: Failed erase", 
and it keep looping the same statement.

Since I may use other filesystem in the future, eg. CRAMFS or VFAT, I 
have no idea on the completeness of the filesystem on the bad block 
managment. So how can enable use the translation layer to manage my bad 
block?

David Woodhouse wrote:

>jason@emsoftltd.com said:
>
>>    Any bad block management routine (eg. Invalid block table ) is
>>implemented for MTD NandFlash driver? It seems that the ECC routine is
>>not enough for my nandflash driver. And  I need a more robust bad
>>block management routine for that.
>>
>
>The low-level hardware driver does not implement and bad block management. 
>That is done by whatever file system or translation layer you use on the 
>flash. What are you intending to use? JFFS2?
>
>--
>dwmw2
>
>


-- 
Best Regards,

Jason Chan
Emsoft Ltd.

Re: Bad Block management routine for MTD NandFlash driver?

[David Woodhouse]

jason@emsoftltd.com said:
>     I trying to use EXT2 for my nandflash driver. Is that OK? 

No. You need _some_ kind of file system which is capable of dealing with 
flash -- either a real file system directly on the flash such as JFFS2, or 
a 'translation layer' like the SmartMedia one or NFTL if you really need to 
use ext2 for some reason.

--
dwmw2

Re: Bad Block management routine for MTD NandFlash driver?

[Jason Chan]

David,
    Sorry, I don't fully understand your 2nd suggestion, 'translation 
layer' like the SmartMedia one.
Is that means the smartmedia mtd driver already has bad block management?

David Woodhouse wrote:

>jason@emsoftltd.com said:
>
>>    I trying to use EXT2 for my nandflash driver. Is that OK? 
>>
>
>No. You need _some_ kind of file system which is capable of dealing with 
>flash -- either a real file system directly on the flash such as JFFS2, or 
>a 'translation layer' like the SmartMedia one or NFTL if you really need to 
>use ext2 for some reason.
>
>--
>dwmw2
>
>


-- 
Best Regards,

Jason Chan
Emsoft Ltd.

Re: Bad Block management routine for MTD NandFlash driver?

[David Woodhouse]

jason@emsoftltd.com said:
>     Sorry, I don't fully understand your 2nd suggestion, 'translation
> layer' like the SmartMedia one. Is that means the smartmedia mtd
> driver already has bad block management? 

You need more than just bad block management. You need a complete file 
system, to give you wear levelling and reliable operation.

The 'mtdblock' driver is not meant for read/write use in normal
circumstances. When you write a sector to the 'mtdblock' device, it reads
the whole erase block from the flash, modifies the sector you wanted to
change, erases the flash erase block and writes back the modified data.

If you lose power or crash between the erase and the writeback, you lose a 
whole erase block of data, not just the sector you were overwriting. And 
there's no wear levelling -- so some blocks will be worn to the point of 
destruction while others still have plenty of life.

You must have some kind of file system on the flash, whether that's a real 
file system such as JFFS2 or a pseudo-filesystem like SmartMedia or NFTL 
which emulates a block device, on top of which you put a 'normal' file 
system.

We don't yet have an implementation of the SmartMedia translation layer in 
CVS, although I think someone _has_ implemented it. NFTL has patent issues 
so I wouldn't advise using that. In fact, emulating a block device is 
the wrong approach entirely -- it's no longer justifiable now that we're 
not using DOS, and you should probably be using JFFS2. 

JFFS2 recognises bad blocks during the medium scan at mount time, and 
does not keep a separate table of bad blocks. If this approach is 
insufficient, patches are welcome. 

--
dwmw2