Zephyr's use of devicetree has evolved significantly over time, and further changes are expected. The following are the general design goals, along with specific examples about how they impact Zephyr's source code, and areas where more work remains to be done.
Zephyr's built-in device drivers and sample applications shall obtain configurable hardware descriptions from devicetree.
- New device drivers shall use devicetree APIs to determine which :ref:`devices to create <dt-create-devices>`.
- In-tree sample applications shall use :ref:`aliases <dt-alias-chosen>` to determine which of multiple possible generic devices of a given type will be used in the current build. For example, the :zephyr:code-sample:`blinky` sample uses this to determine the LED to blink.
- Boot-time pin muxing and pin control for new SoCs shall be accomplished via a devicetree-based pinctrl driver
- Zephyr's :ref:`twister_script` currently use :file:`board.yaml` files to determine the hardware supported by a board. This should be obtained from devicetree instead.
- Legacy device drivers currently use Kconfig to determine which instances of a particular compatible are enabled. This can and should be done with devicetree overlays instead.
- Board-level documentation still contains tables of hardware support which are generated and maintained by hand. This can and should be obtained from the board level devicetree instead.
- Runtime determination of
struct devicerelationships should be done using information obtained from devicetree, e.g. for device power management.
Zephyr's devicetree tooling is based on a generic layer which is interoperable with other devicetree users, such as the Linux kernel.
Zephyr's binding language semantics can support Zephyr-specific attributes, but shall not express Zephyr-specific relationships.
Zephyr's devicetree source parser, :ref:`dtlib.py <dt-scripts>`, is source-compatible with other tools like dtc in both directions: :file:`dtlib.py` can parse
dtcoutput, anddtccan parse :file:`dtlib.py` output.Zephyr's "extended dtlib" library, :file:`edtlib.py`, shall not include Zephyr-specific features. Its purpose is to provide a higher-level view of the devicetree for common elements like interrupts and buses.
Only the high-level :file:`gen_defines.py` script, which is built on top of :file:`edtlib.py`, contains Zephyr-specific knowledge and features.
- Zephyr has a custom :ref:`dt-bindings` language syntax. While Linux's dtschema does not yet meet Zephyr's needs, we should try to follow what it is capable of representing in Zephyr's own bindings.
- Due to inflexibility in the bindings language, Zephyr cannot support the full set of bindings supported by Linux.
- Devicetree source sharing between Zephyr and Linux is not done.