[PATCH] drm/doc: Add KUnit documentation

["José Expósito" <jose.exposito89@gmail.com>]

Explain how to run the KUnit tests present in the DRM subsystem and
clarify why the UML-only options were not added to the configuration
file present in drivers/gpu/drm/.kunitconfig [1] [2].

[1] https://lore.kernel.org/dri-devel/CABVgOSn8i=LO5p7830h2XU1Jgg0KrN0qTnxkOMhf1oTgxjaKKw@mail.gmail.com/
[2] https://lore.kernel.org/dri-devel/CAGS_qxqpiCim_sy1LDK7PLwVgWf-LKW+uNFTGM=T7ydk-dYcEw@mail.gmail.com/

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
---
 Documentation/gpu/drm-internals.rst | 31 +++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/Documentation/gpu/drm-internals.rst b/Documentation/gpu/drm-internals.rst
index 38afed24a75c..08f115417381 100644
--- a/Documentation/gpu/drm-internals.rst
+++ b/Documentation/gpu/drm-internals.rst
@@ -207,6 +207,37 @@ Utilities
    :internal:
 
 
+Unit testing
+============
+
+KUnit
+-----
+
+KUnit (Kernel unit testing framework) provides a common framework for unit tests
+within the Linux kernel.
+
+This section covers the specifics for the DRM subsystem. 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/.kunitconfig``. It can be used by ``kunit.py`` as follows:
+
+.. code-block:: bash
+
+	$ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm \
+		--kconfig_add CONFIG_VIRTIO_UML=y \
+		--kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y
+
+.. note::
+	The configuration included in ``.kunitconfig`` should be as generic as
+	possible.
+	``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not
+	included in it because they are only required for User Mode Linux.
+
+
 Legacy Support Code
 ===================
 
-- 
2.25.1