[U-Boot-Users] NAND and bad blocks

[Stefan Roese <sr@denx.de>]

Hi Matthew,

On Tuesday 18 September 2007, MatthewLCreech at eaton.com wrote:
> 1. How does U-Boot handle a bad block in the area where the environment
> is stored?  I can create a second environment via CFG_ENV_OFFSET_REDUND,
> but that's not very flexible (what if the primary and the backup are
> both bad blocks?)  I also need to write to the environment from within
> Linux via the "fw_setenv" utility, but it doesn't seem to have any NAND
> awareness.

You could be right here. The bad block handling in the NAND environment is not 
perfect. If both blocks of the environment are bad (primary & redundant) then 
we really have a problem.

There was a patch sent to the list a few months ago (IIRC, from the Openmoko 
project), that addressed this problem. Unfortunately I didn't find the time 
till now to take a deeper look at it.

> 2. It's not obvious to me how U-Boot reacts when it encounters a bad
> block.  If I'm copying a kernel image out of NAND, and a bad block is
> encountered, does it skip to the next block?

There are both option:

a) Bad blocks are not skipped and writted as 0xff in memory
b) Bad blocks are skipped upon read from NAND

I personally never used a) and always use b).

> If so, do I need to 
> compensate by padding each partition with unused blocks, or how else
> does addressing work?

Yes, you have to add some reserve to your partitions size for bad blocks that 
could occur.

> Similarly for writes - if I do "nand write 
> <memaddr> <location> 100000", and the first block is bad, will U-Boot
> write all 0x100000 bytes _after_ that block?

Yes.

> 3. Can Linux handle bad blocks in the same manner?  Specifically, I need
> to use 'nandwrite' to copy a kernel image to an MTD partition from
> within Linux, and have U-Boot read the image correctly on bootup, both
> in the presence of bad blocks and bit-flips.

Sure, this works the same way.

Best regards,
Stefan

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