[PATCH v8 4/8] env: Allow U-Boot scripts to be placed in a .env file

[Marek Behún]

On Mon, 18 Oct 2021 12:13:18 -0600
Simon Glass <sjg at chromium.org> wrote:

> At present U-Boot environment variables, and thus scripts, are defined
> by CONFIG_EXTRA_ENV_SETTINGS. It is painful to add large amounts of text
> to this file and dealing with quoting and newlines is harder than it
> should be. It would be better if we could just type the script into a
> text file and have it included by U-Boot.
> 
> Add a feature that brings in a .env file associated with the board
> config, if present. To use it, create a file in a board/<vendor>
> directory, typically called <board>.env and controlled by the
> CONFIG_ENV_SOURCE_FILE option.
> 
> The environment variables should be of the form "var=value". Values can
> extend to multiple lines. See the README under 'Environment Variables:'
> for more information and an example. Note that environment variables may
> not end in + but can start with other strange characters, including
> underscore, comma and slash.
> 
> In many cases environment variables need access to the U-Boot CONFIG
> variables to select different options. Enable this so that the environment
> scripts can be as useful as the ones currently in the board config files.
> This uses the C preprocessor, means that comments can be included in the
> environment using /* ... */
> 
> Also support += to allow variables to be appended to. This is needed when
> using the preprocessor.
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>

Reviewed-by: Marek Behún <marek.behun at nic.cz>
Tested-by: Marek Behún <marek.behun at nic.cz>

Tested on Turris Omnia, but we use distroboot, so will convert only
after distroboot is supported.