Documentation/gpu: Add Display Core Unit Test documentation

Explain how to run the KUnit tests present in the AMDGPU's Display
Core and clarify which architectures and tools can be used to run
the tests. Moreover, explains how to add new tests to the existing
tests.

Signed-off-by: Maíra Canal <mairacanal@riseup.net>

Documentation/gpu/amdgpu/display/display-test.rst

+.. SPDX-License-Identifier: GPL-2.0+
+
+========================
+Display Core Unit Tests
+========================
+
+Display core provides a set of unit tests, currently focused on the Display Mode
+Library. The unit tests use KUnit (Kernel Unit Testing Framework), a common
+framework for unit tests within the Linux Kernel.
+
+This section covers the specifics of the tests for the AMDGPU driver. For general
+information about KUnit, please refer to Documentation/dev-tools/kunit/start.rst.
+
+How to run the tests?
+=====================
+
+In order to facilitate running the test suite, a configuration file is present
+in ``drivers/gpu/drm/amd/display/kunit/dc/.kunitconfig``. This configuration file
+can be used to run the kunit_tool, a Python script (``tools/testing/kunit/kunit.py``)
+used to configure, build, exec, parse and run tests.
+
+.. code-block:: bash
+
+	$ ./tools/testing/kunit/kunit.py run --arch=x86_64 \
+	    --kunitconfig=drivers/gpu/drm/amd/display/kunit
+
+Currently, the Display Core Unit Tests are only supported on x86_64.
+
+Moreover, the tests can also be run on real hardware or in other emulation
+environments. To include the Display Core Unit Tests on a deployable kernel,
+you might add the following config options to your ``.config``:
+
+.. code-block:: none
+
+	CONFIG_KUNIT=y
+	CONFIG_AMDGPU=m
+	CONFIG_AMD_DC_BASICS_KUNIT_TEST=y
+	CONFIG_AMD_DC_KUNIT_TEST=y
+	CONFIG_DCE_KUNIT_TEST=y
+	CONFIG_DML_KUNIT_TEST=y
+
+Once the kernel is built and installed, you can load the ``amdgpu`` module
+to run all tests available.
+
+Also, the tests can be added to the kernel as built-in modules, by adding the
+following config options to your ``.config``:
+
+.. code-block:: none
+
+	CONFIG_KUNIT=y
+	CONFIG_AMDGPU=y
+	CONFIG_AMD_DC_BASICS_KUNIT_TEST=y
+	CONFIG_AMD_DC_KUNIT_TEST=y
+	CONFIG_DCE_KUNIT_TEST=y
+	CONFIG_DML_KUNIT_TEST=y
+
+In order to run specific tests, you can check the filter options from KUnit on
+Documentation/dev-tools/kunit/kunit-tool.rst.
+
+How to add new tests?
+=====================
+
+Tests covering different parts of the Display Core are always welcomed. Adding
+a new test is a simple procedure, that consists in creating a unit test file
+and adding the following guard to the end of the tested file when you are
+testing static functions:
+
+.. code-block:: c
+
+	#ifdef CONFIG_MY_KUNIT_TEST
+	#include "my_kunit_test.c"
+	#endif
+
+If you are not testing static functions, you should use the Makefile placed on
+``display/kunit``. In order to add a test to the Makefile, you can just add
+the following entry to the Makefile:
+
+.. code-block:: make
+
+	ifdef CONFIG_MY_KUNIT_TEST
+		DC_TESTS += my_kunit_test.o
+	endif
+
+The ``display/kunit`` folder replicates the folder hierarchy of the ``display``
+folder, so this must be considered while adding new tests.
+
+More information on how to write unit tests with the KUnit API can be provided
+on Documentation/dev-tools/kunit/api/test.rst.

Documentation/gpu/amdgpu/display/index.rst

@@ -29,4 +29,5 @@ table of content:
    dc-debug.rst
    dcn-overview.rst
    mpo-overview.rst
+   display-test.rst
    dc-glossary.rst