ref-manual: document devicetree class variables

Document the newly added DT_FILES variable and closely related
DT_FILES_PATH. Also add DT_PADDING_SIZE to the glossary.

(From yocto-docs rev: 8f3f187e2353c718c6fb4e224d13ba559ad2f85b)

Signed-off-by: Petr Kubizňák <kubiznak@2n.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 29 insertions, 2 deletions

diff --git a/documentation/ref-manual/classes.rst b/documentation/ref-manual/classes.rst
index ab1628401e..94b6a3ebd7 100644
--- a/documentation/ref-manual/classes.rst
+++ b/documentation/ref-manual/classes.rst
@@ -607,10 +607,15 @@ subdirectory. This avoids clashes with the :ref:`ref-classes-kernel-devicetree`
 output. Additionally, the device trees are populated into the sysroot for
 access via the sysroot from within other recipes.
 
+By default, all device tree sources located in :term:`DT_FILES_PATH` directory
+are compiled. To select only particular sources, set :term:`DT_FILES` to
+a space-separated list of files (relative to :term:`DT_FILES_PATH`). For
+convenience, both ``.dts`` and ``.dtb`` extensions can be used.
+
 An extra padding is appended to non-overlay device trees binaries. This
 can typically be used as extra space for adding extra properties at boot time.
-The padding size can be modified by setting ``DT_PADDING_SIZE`` to the desired
-size, in bytes.
+The padding size can be modified by setting :term:`DT_PADDING_SIZE`
+to the desired size, in bytes.
 
 See :oe_git:`devicetree.bbclass sources
 </openembedded-core/tree/meta/classes-recipe/devicetree.bbclass>` 
diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index 6ee65e1788..4b69843d4d 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -2247,6 +2247,28 @@ system and gives an overview of their function and contents.
       For information on policies and on how to use this variable, see the
       comments in the ``meta/classes-recipe/compress_doc.bbclass`` file.
 
+   :term:`DT_FILES`
+      Space-separated list of device tree source files to compile using
+      a recipe that inherits the :ref:`ref-classes-devicetree` class. These
+      are relative to the :term:`DT_FILES_PATH`.
+
+      For convenience, both ``.dts`` and ``.dtb`` extensions can be used.
+
+      Use an empty string (default) to build all device tree sources within
+      the :term:`DT_FILES_PATH` directory.
+
+   :term:`DT_FILES_PATH`
+      When compiling out-of-tree device tree sources using a recipe that
+      inherits the :ref:`ref-classes-devicetree` class, this variable specifies
+      the path to the directory containing dts files to build.
+
+      Defaults to the :term:`S` directory.
+
+   :term:`DT_PADDING_SIZE`
+      When inheriting the :ref:`ref-classes-devicetree` class, this variable
+      specifies the size of padding appended to the device tree blob, used as
+      extra space typically for additional properties during boot.
+
    :term:`EFI_PROVIDER`
       When building bootable images (i.e. where ``hddimg``, ``iso``, or
       ``wic.vmdk`` is in :term:`IMAGE_FSTYPES`), the