[v2] ref-manual: add documentation for the barebox class

From: Enrico Joerns <ejo@pengutronix.de>

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.

Signed-off-by: Enrico Joerns <ejo@pengutronix.de>
---
v1 -> v2:
  - add link to Kconfig documentation
  - add link to conf/image-uefi.conf in git
  - add example for BAREBOX_BINARY
  - be more specific about BAREBOX_CONFIG usage, its defaults, and
    example values

 documentation/ref-manual/classes.rst   | 37 ++++++++++++++++++++++++++
 documentation/ref-manual/variables.rst | 25 +++++++++++++++++
 2 files changed, 62 insertions(+)

Hi Enrico,

On Fri Jan 17, 2025 at 3:41 PM CET, Enrico Jörns wrote:
> From: Enrico Joerns <ejo@pengutronix.de>
>
> 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.
>
> Signed-off-by: Enrico Joerns <ejo@pengutronix.de>
> ---
> v1 -> v2:
>   - add link to Kconfig documentation
>   - add link to conf/image-uefi.conf in git
>   - add example for BAREBOX_BINARY
>   - be more specific about BAREBOX_CONFIG usage, its defaults, and
>     example values
>
>  documentation/ref-manual/classes.rst   | 37 ++++++++++++++++++++++++++
>  documentation/ref-manual/variables.rst | 25 +++++++++++++++++
>  2 files changed, 62 insertions(+)
>
> diff --git a/documentation/ref-manual/classes.rst b/documentation/ref-manual/classes.rst
> index 22c4301a4..8ad77319e 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``
> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
> index 702a6caf8..e9bffd811 100644
> --- a/documentation/ref-manual/variables.rst
> +++ b/documentation/ref-manual/variables.rst
> @@ -293,6 +293,31 @@ system and gives an overview of their function and contents.
>        :term:`PACKAGE_EXCLUDE` variables for related
>        information.
>  
> +   :term:`BAREBOX_BINARY`

Sorry, I should have said this in v1, but generally we start variable
descriptions that are tied to classes with:

  When using the :ref:`ref-classes-barebox` class, ...

This way, a user reading documentation for the variable knows where it is
originally defined and in which context.

Could you add this for both of these variables?

> +      The barebox build system can build multiple barebox binaries at once.
> +      By default, all built binaries will be deployed and installed under their
> +      original name.
> +      If only a specific binary should be deployed/installed, its name can
> +      be specified in :term:`BAREBOX_BINARY`::
> +
> +        BAREBOX_BINARY = "barebox-boundarydevices-imx6dl-nitrogen6x-1g.img"

Nitpick: we indent code blocks with three spaces, not two.

> +
> +   :term:`BAREBOX_CONFIG`
> +      If set, it specifies the name of the barebox defconfig to build.
> +      The name must be a defconfig file known to the barebox build environment.
> +      This variable is mainly useful for generic use cases where a dedicated
> +      configuration is not required.
> +      The :ref:`ref-classes-barebox` class itself already sets it for some QEMU
> +      machines::
> +
> +        BAREBOX_CONFIG:qemuarm = "multi_v7_defconfig"
> +        BAREBOX_CONFIG:qemuarm64 = "multi_v8_defconfig"
> +        BAREBOX_CONFIG:qemux86-64 = "efi_defconfig"
> +
> +      Except for these, the default value of :term:`BAREBOX_CONFIG` is empty.
> +      For more information on how to provide a barebox configuration, see the
> +      :ref:`ref-classes-barebox` class.
> +
>     :term:`BASE_LIB`
>        The library directory name for the CPU or Application Binary
>        Interface (ABI) tune. The :term:`BASE_LIB` applies only in the Multilib

Otherwise, thank you these look good to me :)

Antonin