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

[Phil Sutter]

Scott,

On Fri, Dec 07, 2012 at 12:53:34PM +0100, Phil Sutter wrote:
> On Thu, Dec 06, 2012 at 12:18:39PM -0600, Scott Wood wrote:
> > On 11/28/2012 03:06:00 PM, Phil Sutter wrote:
> > > 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.
> > 
> > And *that* is what CONFIG_ENV_OFFSET_OOB is supposed to deal with. :-)
> 
> Good to know, I already wondered what exactly this option is there for.

Hmm. Does not look like CONFIG_ENV_OFFSET_OOB is used to select the
block(s) within the erase page to save the environment. Looking at
common/env_nand.c:318, the environment offset saved in the OOB seems to
be in erase page unit.

On the other hand, I could not find code that alters this setting based
on bad blocks found or whatever. This seems to simply be an alternative
to setting CONFIG_ENV_OFFSET at build-time. 

Best wishes,

Phil Sutter
Software Engineer

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