[U-Boot] [PATCH 2/4] env_nand.c: support falling back to redundant env when writing

[Phil Sutter]

Hi,

On Tue, Nov 27, 2012 at 04:04:15PM -0600, Scott Wood wrote:
> On 11/21/2012 06:59:19 AM, Phil Sutter wrote:
> > Without this patch, when the currently chosen environment to be  
> > written
> > has bad blocks, saveenv fails completely. Instead, when there is
> > redundant environment fall back to the other copy. Environment reading
> > needs no adjustment, as the fallback logic for incomplete writes  
> > applies
> > to this case as well.
> > 
> > Signed-off-by: Phil Sutter <phil.sutter at viprinet.com>
> 
> Isn't this what CONFIG_ENV_RANGE is supposed to deal with?

Yes, that is more or less what is supposed to help for cases like this.
But given the fact that CONFIG_ENV_RANGE needs to span multiple erase
pages which in our case are 128k in size, this is quite a deal.
Especially since one needs to have multiple pages for both normal and
redundant environment to be really sure.

But, we already have a fixed hashmap in field, so using CONFIG_ENV_RANGE
is simply no option.

> Redundant environment is to deal with other problems such as a power  
> failure during saveenv.  If you just fall back to the other copy,  
> you're silently losing the redundancy.

The alternative to silently losing redundancy in case one of the blocks
in either normal or redundant env areas turns bad is to not being able
to save the environment at all anymore. I'd prefer dropping the
redundancy but still having a working system then. ;)

Best wishes and thanks for the review,

Phil Sutter
Software Engineer

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