[U-Boot] [PATCH v3] NAND: environment offset in OOB (CONFIG_ENV_OFFSET_OOB)

[Ben Gardiner]

On Wed, Jun 30, 2010 at 5:41 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Ben Gardiner,
>
> In message <1277933528-8335-1-git-send-email-bengardiner at nanometrics.ca> you wrote:
>> This is a re-submission of the patch by Harald Welte
>> <laforge at openmoko.org> with minor modifications for rebase and changes
>> as suggested by Scott Wood <scottwood at freescale.com> [1] [2].
>>
>> This patch enables the environment partition to have a run-time dynamic
>> location (offset) in the NAND flash.  The reason for this is simply that
>> all NAND flashes have factory-default bad blocks, and a fixed compile
>> time offset would mean that sometimes the environment partition would
>> live inside factory bad blocks. Since the number of factory default
>> blocks can be quite high (easily 1.3MBytes in current standard
>> components), it is not economic to keep that many spare blocks inside
>> the environment partition.
>>
>> With this patch and CONFIG_ENV_OFFSET_OOB enabled, the location of the
>> environment partition is stored in the out-of-band (OOB) data of the
>> first block in flash. Since the first block is where most systems boot
>> from, the vendors guarantee that the first block is not a factory
>> default block.
>
> Does this work with redundant environment in NAND?

Currently the use of CONFIG_ENV_OFFSET_OOB and
CONFIG_ENV_OFFSET_REDUND is disabled. I think it could work when the
env is in its own NAND partition (i.e. !ENV_IS_EMBEDDED and
!CONFIG_NAND_ENV_DST).

We could require that the redundant env is CONFIG_ENV_SIZE after the
offset specified in the OOB or that two offsets are store in the OOB
area. The latter requires that the OOB size is large enough to store
two offsets. The former requires that CONFIG_ENV_SIZE is a multiple of
the erase block size and perhaps additional skip-if-bad-block
behaviour.

Furthermore, to implement env.oob compatibility with redundant
environments I believe that the use of the CONFIG_ENV_OFFSET_REDUND
macro needs to be split into a 'use redundant env' macro and a 'value
of redundant env offset' macro so that we don't have to redefine
CONFIG_ENV_OFFSET_REDUND. For instance, I would change saveenv in
env_nand.c to look something like:

---

#ifdef CONFIG_USE_ENV_REDUND
int saveenv(void)
{
...
                ret = writeenv(CONFIG_ENV_OFFSET_REDUND, (u_char *) env_ptr);

---

I see that compatibility of this feature with redundant environments
would definitely increase its utility. Can I put that into a second
patch series and leave this patch as-is to be considered for
inclusion? Would you prefer that I re-spin this patch into a series
that includes support for redundant environment?

Best Regards,
Ben Gardiner

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