[PATCH v9 5/7] doc: Mention CONFIG_DEFAULT_ENV_FILE

[Simon Glass]

Add mention of this option since it does a similar thing to the text
environment.

Signed-off-by: Simon Glass <sjg at chromium.org>
Suggested-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
Reviewed-by: Marek Behún <marek.behun at nic.cz>
---

Changes in v9:
- Fix blank line between tags
- Fix typo in commit message

Changes in v8:
- Fix ambiguity about what is ignored

Changes in v7:
- Add new patch to explain the relationship with DEFAULT_ENV_FILE

 doc/usage/environment.rst | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index 667fd193ea1..adf2e067b58 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -454,3 +454,18 @@ The signature of the callback functions is::
   include/search.h
 
 The return value is 0 if the variable change is accepted and 1 otherwise.
+
+
+External environment file
+-------------------------
+
+The `CONFIG_USE_DEFAULT_ENV_FILE` option provides a way to bypass the
+environment generation in U-Boot. If enabled, then `CONFIG_DEFAULT_ENV_FILE`
+provides the name of a file which is converted into the environment,
+completely bypassing the standard environment variables in `env_default.h`.
+
+The format is the same as accepted by the mkenvimage tool, with lines containing
+key=value pairs. Blank lines and lines beginning with # are ignored.
+
+Future work may unify this feature with the text-based environment, perhaps
+moving the contents of `env_default.h` to a text file.
-- 
2.33.0.1079.g6e70778dc9-goog