[U-Boot-Users] bootargs for partitioned nand flash

[Detlev Zundel]

Hi Norman,

> Wolfgang Denk <wd <at> denx.de> writes:
>
>> 
>> In message <OF59F26445.61F7D04D-ON48257125.002C708D-48257125.002CF471 <at>
> applera.com> you wrote:
>
>> 
>> Also note that a cramfs may fail  to  work  in  case  there  are  bad
>> sectors in your NAND device.
>> 
>
> Wolfgang, this might be an off topic here.  I have a client requirement to have
> a  RFS like cramfs or squashfs on NAND.

Check the available documentation on NAND devices.  I found this
application note to be a real eye opener[1].  Especially the section
"NAND Flash is Not a Hard Drive" is a must read.  Maybe you reconsider
the requirement.

> If I use the u-boot nand write command to write the cramfs to a MTD
> partition.  How does nand write treat a bad block?

What part of this section from doc/README.nand is not clear to you?

   nand write.jffs2 addr ofs|partition size
      Like `write', but blocks that are marked bad are skipped and the
      data is written to the next block instead. This allows writing a
      JFFS2 image, as long as the image is short enough to fit even
      after skipping the bad blocks. Compact images, such as those
      produced by mkfs.jffs2 should work well, but loading an image
      copied from another flash is going to be trouble if there are any
      bad block

> I am thinking that if nand write skip to the next block, then I might
> be able to modify nand read...  Or is there a better way?

What does the block layer of MTD in linux do?  This is a much more
interesting question.  As far as I can see, this layer will not be able
to handle any bad blocks.

Unless I don't see a very clever solution, putting such a filesystem on
a flaky substrate like NAND really needs another layer handling the
shuffling around - UBI comes to mind here, but I do not have any
experiences with it (yet).

Cheers
  Detlev

[1] http://download.micron.com/pdf/technotes/nand/tn2917.pdf

-- 
These days, even the most pure and abstract mathematics is in danger
to be applied.
--
DENX Software Engineering GmbH,      MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich,  Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-40 Fax: (+49)-8142-66989-80 Email: dzu at denx.de