[U-Boot] incremental environment updating

[Mike Frysinger <vapier@gentoo.org>]

On Monday 13 April 2009 06:15:24 Wolfgang Denk wrote:
> In message Mike wrote:
> > currently the env code will erase the entire env storage before writing
> > back out the current env, even if the env storage has enough empty space
> > to store the current env.  for example, if CONFIG_ENV_SIZE is declared as
> > 0x2000 but the current env only takes up ~0x300 bytes, the whole 0x2000
> > is erased and then the ~0x300 gets written out.  seems like we can get a
> > pretty good return for fairly low effort if we appended env updates
> > rather than erasing/writing every time ?  it'd certainly be faster. 
> > while systems with a dedicated sector this isnt so bad, but for people
> > who have to embed the env in the middle of a large sector, this would be
> > much faster most of the time.
> >
> > has there been previous discussion along these lines that i havent seen ?
>
> This hasn't been discussed before. Interesting idea. However, I fail
> to see how this could be implemented without changing the environment
> format?

that depends on how you want the compatibility to go.  being able to read old 
environments by newer u-boots is reasonable, but i dont think having old u-
boots read newer environments makes realistic sense ?

in terms of actual changes, i had a couple of ideas ... the current env format 
is: <crc><env><NUL>[undefined].  so if we logically extend the format where 
[undefined] is <crc><env><NUL>[...], then all existing env storage would be 
automatically imported.  considering most env storage out there uses a bit 
value of "0" to mean programmed and "1' to mean unprogrammed, it should be 
pretty easy to quickly detect where the appended envs stop.
-mike
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