docs: add a section for experimental build options
A number of features are marked experimental in the build system through
makefiles but there wasn't an explicit document to list them.
Added a dedicated experimental build options section and moved
existing experimental build option descriptions in this section.
Restoring the change from [1] removing the experimental flag on the EL3
SPMC (this has been lost in rebasing a later change).
[1] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/24713
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I2c458c6857c347114b265404e8b9ede9ac588463
diff --git a/docs/about/features.rst b/docs/about/features.rst
index 4a2c77e..c12509d 100644
--- a/docs/about/features.rst
+++ b/docs/about/features.rst
@@ -108,6 +108,28 @@
- Position-Independent Executable (PIE) support.
+Experimental features
+---------------------
+
+A feature is considered experimental when still in development or isn't known
+to the TF-A team as widely deployed or proven on end products. It is generally
+advised such options aren't pulled into real deployments, or done with the
+appropriate level of supplementary integration testing.
+
+A feature is no longer considered experimental when it is generally agreed
+the said feature has reached a level of maturity and quality comparable to
+other features that have been integrated into products.
+
+Experimental build options are found in following section
+:ref:`build_options_experimental`. Their use through the build emits a warning
+message.
+
+Additionally the following libraries are marked experimental when included
+in a platform:
+
+- MPU translation library ``lib/xlat_mpu``
+- RSS comms driver ``drivers/arm/rss``
+
Still to come
-------------