ref-manual: cover UBOOT_ENV variables

(From yocto-docs rev: dc2ff96a3401eba8dac86fc8305b261be52c8a13)

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/variables.rst

@@ -3183,6 +3183,31 @@ system and gives an overview of their function and contents.
       The default value for this variable is set to "2048"
       by the :ref:`ref-classes-kernel-fitimage` class.
 
+   :term:`FIT_UBOOT_ENV`
+      This variable allows to add a U-Boot script as a text file to the
+      FIT image. Such a script can be sourced from the U-Boot shell.
+
+      When inheriting the :ref:`ref-classes-kernel-fitimage` class a
+      script file should be included in the :term:`SRC_URI` of the Linux
+      kernel recipe.
+
+      Example:
+
+      -  Add a script ``boot.cmd`` to the Linux kernel recipe::
+
+            FIT_UBOOT_ENV = "boot.cmd"
+            SRC_URI += "file://${FIT_UBOOT_ENV}"
+
+      -  Use the script file from the U-Boot shell. The name of the script in
+         FIT image is ``bootscr-${FIT_UBOOT_ENV}``. This example loads the FIT
+         image from a TFTP server::
+
+            tftp $loadaddr $fit_tftp_path
+            source $loadaddr#bootscr-boot.cmd
+
+      More information can be found in the official U-Boot documentation:
+      `U-Boot source command <https://docs.u-boot.org/en/latest/usage/cmd/source.html#fit-image.f>`__
+
    :term:`FONT_EXTRA_RDEPENDS`
       When inheriting the :ref:`ref-classes-fontcache` class,
       this variable specifies the runtime dependencies for font packages.
@@ -9807,6 +9832,44 @@ system and gives an overview of their function and contents.
       :ref:`ref-classes-uboot-config` and :ref:`ref-classes-uboot-sign`
       classes.
 
+   :term:`UBOOT_ENV`
+      This variable allows to add additional environment variables or a script
+      to be installed together with U-Boot.
+      This file, typically ``uEnv.txt`` or ``boot.cmd``, is installed in
+      ``/boot`` as well as copied to the :term:`DEPLOYDIR` directory.
+
+      For machine configurations needing one of these files a ``.bbappend``
+      file should include it in the :term:`SRC_URI` of the U-Boot recipe.
+
+      If the variable :term:`UBOOT_ENV_SUFFIX` is set to ``scr`` the script is
+      packaged as a uImage (``mkimage -T script..``) otherwise it gets
+      installed verbatim.
+
+      Some examples:
+
+      -  Adding a script ``boot.cmd`` as a uImage to ``/boot``::
+
+            UBOOT_ENV = "boot"
+            UBOOT_ENV_SUFFIX = "scr"
+            SRC_URI += "file://${UBOOT_ENV_SRC}"
+
+      -  Adding a script ``uEnv.txt`` as a plain text file to ``/boot``::
+
+            UBOOT_ENV = "uEnv"
+            UBOOT_ENV_SUFFIX = "txt"
+            SRC_URI += "file://${UBOOT_ENV_BINARY}"
+
+   :term:`UBOOT_ENV_SRC_SUFFIX`
+      If :term:`UBOOT_ENV_SUFFIX` is set to ``scr`` this is the suffix of the
+      plain text script file as it is specified in the :term:`SRC_URI` of the
+      U-Boot recipe. It defaults to ``cmd``.
+
+   :term:`UBOOT_ENV_SUFFIX`
+      If this variable is set to ``scr`` the script referred to by
+      :term:`UBOOT_ENV` gets packaged as a uImage before it gets installed.
+      The default is ``txt`` which means the script is installed as-is, with
+      no modification.
+
    :term:`UBOOT_FIT_ADDRESS_CELLS`
       Specifies the value of the ``#address-cells`` value for the
       description of the U-Boot FIT image.