[PATCH 4/5] env: allow default environment to be amended from control dtb

[Rasmus Villemoes]

On 20/11/2020 11.13, Wolfgang Denk wrote:
> Dear Rasmus,
> 
> In message <76615995-6700-1b3e-b598-4913e9882c26 at prevas.dk> you wrote:
>>
>> Sure. So would you be ok with some /config/extra-environment node which
>> gets appended after the normal environment has been loaded? Then if I
> 
> In principle yes, I see that this is a nice and useful feature.
> 
> Just the notation of "append" seems wrong to me.  We already have
> "env import" which can import additional / new environmane settings
> in different formats.  What I think should be done is extending this
> by support for a new format (you may call it driver if you want)
> to import environment settings from a DTB.
> 
>> set CONFIG_ENV_IS_NOWHERE, I'd get what I have now. The only problem
> 
> Can't you see that this is not logical?  If the environment is
> nowhere, then how can you add something to it?

That's silly. Even with CONFIG_ENV_IS_NOWHERE, "env set" still works
just fine. So of course one can add something to the (runtime)
environment, even if the source of the original runtime environment
happened to be default_environment[] and those changes cannot be persisted.

>>> I wonder if we should have a way to load the (whole) environment from DT?
>>
>> That will be my second choice, i.e. adding a "CONFIG_ENV_IS_IN_DTB"
>> which obviously doesn't support saving, but has the advantages I'm after
>> here of using one U-Boot binary with slightly different environments.
> 
> I see no difference here.  "env import" into an empty environment
> does just that.

The problem is, by the time it's possible to do an "env import" (no
sooner than $preboot is executed I assume?) or any other shell command,
U-Boot may already have read a bunch variables affecting its execution
from the environment.

So I think that for my _current_ use cases, doing it via a preboot
command may be enough - from reading the code, it does seem that e.g.
bootretry is only read after the preboot command has run.

I'll see if I can come up with something else.

Rasmus