ref-manual: add documentation for the barebox class

This adds the initial documentation for the newly added barebox.bbclass
to the Reference Manual's class list.
It also adds the two most notable variables to the variable list.

(From yocto-docs rev: cc8179122441cdc26ff62511dcd97f7bf9bf7e3d)

Signed-off-by: Enrico Jörns <ejo@pengutronix.de>
Reviewed-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/documentation/ref-manual/classes.rst b/documentation/ref-manual/classes.rst
index 22c4301a49..8ad77319ec 100644
--- a/documentation/ref-manual/classes.rst
+++ b/documentation/ref-manual/classes.rst
@@ -128,6 +128,43 @@ It's useful to have some idea of how the tasks defined by the
 -  :ref:`ref-tasks-install` --- runs ``make install`` and
    passes in ``${``\ :term:`D`\ ``}`` as ``DESTDIR``.
 
+.. _ref-classes-barebox:
+
+``barebox``
+===========
+
+The :ref:`ref-classes-barebox` class manages building the barebox bootloader.
+
+If a file named ``defconfig`` is included in the :term:`SRC_URI`, it will be
+copied to ``.config`` in the build directory and used as the barebox
+configuration.
+Instead of providing a ``defconfig`` file, you can set :term:`BAREBOX_CONFIG`
+to a defconfig provided by the barebox source tree.
+If neither ``defconfig`` nor :term:`BAREBOX_CONFIG` is specified, the class
+will raise an error.
+
+The :ref:`ref-classes-barebox` class supports config fragments and internally
+includes the :ref:`ref-classes-cml1` class to provide `Kconfig
+<https://docs.kernel.org/kbuild/kconfig-language.html>`__ support for
+barebox, enabling tasks such as :ref:`ref-tasks-menuconfig` and
+:ref:`ref-tasks-diffconfig`.
+
+The generated barebox binaries are deployed to
+:term:`DEPLOY_DIR_IMAGE` as well as installed to ``BAREBOX_INSTALL_PATH``
+(``/boot`` by default) making them part of the recipe’s base package.
+This setup supports both using the barebox binaries as independent artifacts
+and installing them into a rootfs.
+:term:`BAREBOX_BINARY` can be used to select a distinct binary to deploy and
+install.
+If ``barebox`` is set as the :term:`EFI_PROVIDER`, the class will leverage
+:oe_git:`conf/image-uefi.conf </openembedded-core/tree/meta/conf/image-uefi.conf>`
+to define the default installation paths and naming conventions.
+
+The compiled-in barebox environment can be extended by adding environment files
+to the ``BAREBOX_ENV_DIR``.
+The ``BAREBOX_FIRMWARE_DIR`` variable allows you to specify the firmware blob
+search directory, enabling loading of additional firmware like TF-A or OP-TEE.
+
 .. _ref-classes-base:
 
 ``base``