drm/vc4: tests: Introduce a mocking infrastructure

In order to test the current atomic_check hooks we need to have a DRM
device that has roughly the same capabilities and layout that the actual
hardware. We'll also need a bunch of functions to create arbitrary
atomic states.

Let's create some helpers to create a device that behaves like the real
one, and some helpers to maintain the atomic state we want to check.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Link: https://lore.kernel.org/r/20221123-rpi-kunit-tests-v3-17-4615a663a84a@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/tests/vc4_mock_plane.c

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <drm/drm_atomic_state_helper.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_modeset_helper_vtables.h>
+#include <drm/drm_plane.h>
+
+#include <kunit/test.h>
+
+#include "vc4_mock.h"
+
+static const struct drm_plane_helper_funcs vc4_dummy_plane_helper_funcs = {
+};
+
+static const struct drm_plane_funcs vc4_dummy_plane_funcs = {
+	.atomic_destroy_state	= drm_atomic_helper_plane_destroy_state,
+	.atomic_duplicate_state	= drm_atomic_helper_plane_duplicate_state,
+	.reset			= drm_atomic_helper_plane_reset,
+};
+
+static const uint32_t vc4_dummy_plane_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+struct vc4_dummy_plane *vc4_dummy_plane(struct kunit *test,
+					struct drm_device *drm,
+					enum drm_plane_type type)
+{
+	struct vc4_dummy_plane *dummy_plane;
+	struct drm_plane *plane;
+
+	dummy_plane = drmm_universal_plane_alloc(drm,
+						 struct vc4_dummy_plane, plane.base,
+						 0,
+						 &vc4_dummy_plane_funcs,
+						 vc4_dummy_plane_formats,
+						 ARRAY_SIZE(vc4_dummy_plane_formats),
+						 NULL,
+						 DRM_PLANE_TYPE_PRIMARY,
+						 NULL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dummy_plane);
+
+	plane = &dummy_plane->plane.base;
+	drm_plane_helper_add(plane, &vc4_dummy_plane_helper_funcs);
+
+	return dummy_plane;
+}