zephyr/doc/build/dts/troubleshooting.rst

.. _dt-trouble:

Troubleshooting devicetree
##########################

Here are some tips for fixing misbehaving devicetree related code.

See :ref:`dt-howtos` for other "HOWTO" style information.

.. _dt-trouble-try-pristine:

Try again with a pristine build directory
*****************************************

.. important:: Try this first, before doing anything else.

See :ref:`west-building-pristine` for examples, or just delete the build
directory completely and retry.

This is general advice which is especially applicable to debugging devicetree
issues, because the outputs are created during the CMake configuration phase,
and are not always regenerated when one of their inputs changes.

Make sure <devicetree.h> is included
************************************

Unlike Kconfig symbols, the :file:`devicetree.h` header must be included
explicitly.

Many Zephyr header files rely on information from devicetree, so including some
other API may transitively include :file:`devicetree.h`, but that's not
guaranteed.

undefined reference to ``__device_dts_ord_<N>``
***********************************************

This usually happens on a line like this:

.. code-block:: c

   const struct device *dev = DEVICE_DT_GET(NODE_ID);

where ``NODE_ID`` is a valid :ref:`node identifier <dt-node-identifiers>`, but
no device driver has allocated a ``struct device`` for this devicetree node.
You thus get a linker error, because you're asking for a pointer to a device
that isn't defined.

To fix it, you need to make sure that:

1. The node is enabled: the node must have ``status = "okay";``.

   (Recall that a missing ``status`` property means the same thing as ``status
   = "okay";``; see :ref:`dt-important-props` for more information about
   ``status``).

2. A device driver responsible for allocating the ``struct device`` is enabled.
   That is, the Kconfig option which makes the build system compile the driver
   sources into your application needs to be set to ``y``.

   (See :ref:`setting_configuration_values` for more information on setting
   Kconfig options.)

Below, ``<build>`` means your build directory.

**Making sure the node is enabled**:

To find the devicetree node you need to check, use the number ``<N>`` from the
linker error. Look for this number in the list of nodes at the top of
:file:`<build>/zephyr/include/generated/devicetree_generated.h`. For example, if
``<N>`` is 15, and your :file:`devicetree_generated.h` file looks like this,
the node you are interested in is ``/soc/i2c@deadbeef``:

.. code-block:: none

   /*
    * Generated by gen_defines.py
    *
    * DTS input file:
    *   <build>/zephyr/zephyr.dts.pre
    *
    * Directories with bindings:
    *   $ZEPHYR_BASE/dts/bindings
    *
    * Node dependency ordering (ordinal and path):
    *   0   /
    *   1   /aliases
   [...]
    *   15  /soc/i2c@deadbeef
   [...]

Now look for this node in :file:`<build>/zephyr/zephyr.dts`, which is the final
devicetree for your application build. (See :ref:`get-devicetree-outputs` for
information and examples.)

If the node has ``status = "disabled";`` in :file:`zephyr.dts`, then you need
to enable it by setting ``status = "okay";``, probably by using a devicetree
:ref:`overlay <set-devicetree-overlays>`. For example, if :file:`zephyr.dts`
looks like this:

.. code-block:: DTS

   i2c0: i2c@deadbeef {
           status = "disabled";
   };

Then you should put this into your devicetree overlay and
:ref:`dt-trouble-try-pristine`:

.. code-block:: DTS

   &i2c0 {
           status = "okay";
   };

Make sure that you see ``status = "okay";`` in :file:`zephyr.dts` after you
rebuild.

**Making sure the device driver is enabled**:

The first step is to figure out which device driver is responsible for handling
your devicetree node and allocating devices for it. To do this, you need to
start with the ``compatible`` property in your devicetree node, and find the
driver that allocates ``struct device`` instances for that compatible.

If you're not familiar with how devices are allocated from devicetree nodes
based on compatible properties, the ZDS 2021 talk `A deep dive into the Zephyr
2.5 device model`_ may be a useful place to start, along with the
:ref:`device_model_api` pages. See :ref:`dt-important-props` and the Devicetree
specification for more information about ``compatible``.

.. _A deep dive into the Zephyr 2.5 device model:
   https://www.youtube.com/watch?v=sWaxQyIgEBY

There is currently no documentation for what device drivers exist and which
devicetree compatibles they are associated with. You will have to figure this
out by reading the source code:

- Look in :zephyr_file:`drivers` for the appropriate subdirectory that
  corresponds to the API your device implements
- Look inside that directory for relevant files until you figure out what the
  driver is, or realize there is no such driver.

Often, but not always, you can find the driver by looking for a file that sets
the ``DT_DRV_COMPAT`` macro to match your node's ``compatible`` property,
except lowercased and with special characters converted to underscores. For
example, if your node's compatible is ``vnd,foo-device``, look for a file with this
line:

.. code-block:: C

   #define DT_DRV_COMPAT vnd_foo_device

.. important::

   This **does not always work** since not all drivers use ``DT_DRV_COMPAT``.

If you find a driver, you next need to make sure the Kconfig option that
compiles it is enabled. (If you don't find a driver, and you are sure the
compatible property is correct, then you need to write a driver. Writing
drivers is outside the scope of this documentation page.)

Continuing the above example, if your devicetree node looks like this now:

.. code-block:: DTS

   i2c0: i2c@deadbeef {
           compatible = "nordic,nrf-twim";
           status = "okay";
   };

Then you would look inside of :zephyr_file:`drivers/i2c` for the driver file
that handles the compatible ``nordic,nrf-twim``. In this case, that is
:zephyr_file:`drivers/i2c/i2c_nrfx_twim.c`. Notice how even in cases where
``DT_DRV_COMPAT`` is not set, you can use information like driver file names as
clues.

Once you know the driver you want to enable, you need to make sure its Kconfig
option is set to ``y``. You can figure out which Kconfig option is needed by
looking for a line similar to this one in the :file:`CMakeLists.txt` file in
the drivers subdirectory. Continuing the above example,
:zephyr_file:`drivers/i2c/CMakeLists.txt` has a line that looks like this:

.. code-block:: cmake

   zephyr_library_sources_ifdef(CONFIG_NRFX_TWIM       i2c_nrfx_twim.c)

This means that :kconfig:option:`CONFIG_NRFX_TWIM` must be set to ``y`` in
:file:`<build>/zephyr/.config` file.

If your driver's Kconfig is not set to ``y``, you need to figure out what you
need to do to make that happen. Often, this will happen automatically as soon
as you enable the devicetree node. Otherwise, it is sometimes as simple as
adding a line like this to your application's :file:`prj.conf` file and then
making sure to :ref:`dt-trouble-try-pristine`:

.. code-block:: cfg

   CONFIG_FOO=y

where ``CONFIG_FOO`` is the option that :file:`CMakeLists.txt` uses to decide
whether or not to compile the driver.

However, there may be other problems in your way, such as unmet Kconfig
dependencies that you also have to enable before you can enable your driver.

Consult the Kconfig file that defines ``CONFIG_FOO`` (for your value of
``FOO``) for more information.

.. _dt-use-the-right-names:

Make sure you're using the right names
**************************************

Remember that:

- In C/C++, devicetree names must be lowercased and special characters must be
  converted to underscores. Zephyr's generated devicetree header has DTS names
  converted in this way into the C tokens used by the preprocessor-based
  ``<devicetree.h>`` API.
- In overlays, use devicetree node and property names the same way they
  would appear in any DTS file. Zephyr overlays are just DTS fragments.

For example, if you're trying to **get** the ``clock-frequency`` property of a
node with path ``/soc/i2c@12340000`` in a C/C++ file:

.. code-block:: c

   /*
    * foo.c: lowercase-and-underscores names
    */

   /* Don't do this: */
   #define MY_CLOCK_FREQ DT_PROP(DT_PATH(soc, i2c@1234000), clock-frequency)
   /*                                           ^               ^
    *                                        @ should be _     - should be _  */

   /* Do this instead: */
   #define MY_CLOCK_FREQ DT_PROP(DT_PATH(soc, i2c_1234000), clock_frequency)
   /*                                           ^               ^           */

And if you're trying to **set** that property in a devicetree overlay:

.. code-block:: none

   /*
    * foo.overlay: DTS names with special characters, etc.
    */

   /* Don't do this; you'll get devicetree errors. */
   &{/soc/i2c_12340000/} {
   	clock_frequency = <115200>;
   };

   /* Do this instead. Overlays are just DTS fragments. */
   &{/soc/i2c@12340000/} {
   	clock-frequency = <115200>;
   };

Look at the preprocessor output
*******************************

To save preprocessor output files, enable the
:kconfig:option:`CONFIG_COMPILER_SAVE_TEMPS` option. For example, to build
:ref:`hello_world` with west with this option set, use:

.. code-block:: sh

   west build -b BOARD samples/hello_world -- -DCONFIG_COMPILER_SAVE_TEMPS=y

This will create a preprocessor output file named :file:`foo.c.i` in the build
directory for each source file :file:`foo.c`.

You can then search for the file in the build directory to see what your
devicetree macros expanded to. For example, on macOS and Linux, using ``find``
to find :file:`main.c.i`:

.. code-block:: sh

   $ find build -name main.c.i
   build/CMakeFiles/app.dir/src/main.c.i

It's usually easiest to run a style formatter on the results before opening
them. For example, to use ``clang-format`` to reformat the file in place:

.. code-block:: sh

   clang-format -i build/CMakeFiles/app.dir/src/main.c.i

You can then open the file in your favorite editor to view the final C results
after preprocessing.

Do not track macro expansion
****************************

Compiler messages for devicetree errors can sometimes be very long. This
typically happens when the compiler prints a message for every step of a
complex macro expansion that has several intermediate expansion steps.

To prevent the compiler from doing this, you can disable the
:kconfig:option:`CONFIG_COMPILER_TRACK_MACRO_EXPANSION` option. This typically
reduces the output to one message per error.

For example, to build :ref:`hello_world` with west and this option disabled,
use:

.. code-block:: sh

   west build -b BOARD samples/hello_world -- -DCONFIG_COMPILER_TRACK_MACRO_EXPANSION=n

Validate properties
*******************

If you're getting a compile error reading a node property, check your node
identifier and property. For example, if you get a build error on a line that
looks like this:

.. code-block:: c

   int baud_rate = DT_PROP(DT_NODELABEL(my_serial), current_speed);

Try checking the node by adding this to the file and recompiling:

.. code-block:: c

   #if !DT_NODE_EXISTS(DT_NODELABEL(my_serial))
   #error "whoops"
   #endif

If you see the "whoops" error message when you rebuild, the node identifier
isn't referring to a valid node. :ref:`get-devicetree-outputs` and debug from
there.

Some hints for what to check next if you don't see the "whoops" error message:

- did you :ref:`dt-use-the-right-names`?
- does the :ref:`property exist <dt-checking-property-exists>`?
- does the node have a :ref:`matching binding <dt-bindings>`?
- does the binding define the property?

.. _missing-dt-binding:

Check for missing bindings
**************************

See :ref:`dt-bindings` for information about bindings, and
:ref:`devicetree_binding_index` for information on bindings built into Zephyr.

If the build fails to :ref:`dts-find-binding` for a node, then either the
node's ``compatible`` property is not defined, or its value has no matching
binding. If the property is set, check for typos in its name. In a devicetree
source file, ``compatible`` should look like ``"vnd,some-device"`` --
:ref:`dt-use-the-right-names`.

If your binding file is not under :file:`zephyr/dts`, you may need to set
:ref:`DTS_ROOT <dts_root>`; see :ref:`dt-where-bindings-are-located`.

Errors with DT_INST_() APIs
***************************

If you're using an API like :c:func:`DT_INST_PROP`, you must define
``DT_DRV_COMPAT`` to the lowercase-and-underscores version of the compatible
you are interested in. See :ref:`dt-create-devices-inst`.