summaryrefslogtreecommitdiffstats
path: root/Documentation
diff options
context:
space:
mode:
authorAhmad Fatoum <a.fatoum@pengutronix.de>2019-09-23 14:10:18 +0200
committerSascha Hauer <s.hauer@pengutronix.de>2019-10-02 08:48:03 +0200
commitca61d55f8e4a4ce1e2ebf850699c756a19324d83 (patch)
tree93cc8562637b0b1dad5f2f8f40464e6cc80c8397 /Documentation
parent9d0469550097b84c7b0cae5179e6297f0ce9b34c (diff)
downloadbarebox-ca61d55f8e4a4ce1e2ebf850699c756a19324d83.tar.gz
Documentation: document barebox device tree handling
The way barebox handles the Linux device trees and the device tree compiler source included in the source tree may not be obvious to new developers. Add a basic high-level documentation. Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/devicetree/index.rst59
1 files changed, 57 insertions, 2 deletions
diff --git a/Documentation/devicetree/index.rst b/Documentation/devicetree/index.rst
index c6309de..9086526 100644
--- a/Documentation/devicetree/index.rst
+++ b/Documentation/devicetree/index.rst
@@ -1,5 +1,60 @@
-Barebox specific devicetree bindings
-====================================
+Barebox devicetree handling and bindings
+========================================
+
+The preferred way of adding board support to barebox is to have devices
+on non-enumerable buses probed from device tree.
+barebox imports the Linux OpenFirmware ``of_*``-API functions for device tree
+parsing, which makes porting the device tree specific bits from device drivers
+very straight forward.
+
+Additionally, barebox has support for programmatically fixing up device trees
+it passes to the kernel, either directly via ``of_register_fixup`` or via device
+tree overlays.
+
+Upstream Device Trees
+---------------------
+
+barebox regularly synchronizes with the Linux kernel device tree definitions
+via the `kernel.org Split device-tree repository`_.
+They are located under the top-level ``dts/`` directory.
+
+Patches against ``dts/`` and its subdirectories are not accepted upstream.
+
+.. _kernel.org Split device-tree repository: https://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git/
+
+barebox Device Trees
+--------------------
+
+For supporting architectures, barebox device trees are located in
+``arch/$ARCH/dts``. Usually the barebox ``board.dts`` imports the upstream
+device tree under ``dts/src/$ARCH`` with ``#include "$ARCH/board.dts"`` and
+then extends it with barebox-specifics like :ref:`barebox,state`,
+environment or boot-time device configuration.
+
+Device Tree Compiler
+--------------------
+
+barebox makes use of the ``dtc`` and ``fdtget`` and the underlying ``libfdt``
+from the `Device-Tree Compiler`_ project.
+
+.. _Device-Tree Compiler: https://git.kernel.org/pub/scm/utils/dtc/dtc.git
+
+These utilities are built as part of the barebox build process. Additionally,
+libfdt is compiled once more as part of the ``CONFIG_BOARD_ARM_GENERIC_DT``
+if selected.
+
+Steps to update ``scripts/dtc``:
+
+* Place a ``git-checkout`` of the upstream ``dtc`` directory in the parent
+ directory of your barebox ``git-checkout``.
+* Run ``scripts/dtc/update-dtc-source.sh`` from the top-level barebox directory.
+* Wait till ``dtc`` build, test, install and commit conclude.
+* Compile-test with ``CONFIG_BOARD_ARM_GENERIC_DT=y``.
+* If ``scripts/dtc/Makefile`` or barebox include file changes are necessary,
+ apply them manually in a commit preceding the ``dtc`` update.
+
+barebox-specific Bindings
+-------------------------
Contents: