drm/tests: Add HDMI connector rate filter hook tests

The previous patch adds a new hook for HDMI connectors to filter out
configurations based on the TMDS character rate. Let's add some tests to
make sure it works as expected.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240527-kms-hdmi-connector-state-v15-14-c5af16c3aae2@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/tests/drm_hdmi_state_helper_test.c

@@ -115,6 +115,18 @@ static int set_connector_edid(struct kunit *test, struct drm_connector *connecto
 static const struct drm_connector_hdmi_funcs dummy_connector_hdmi_funcs = {
 };
 
+static enum drm_mode_status
+reject_connector_tmds_char_rate_valid(const struct drm_connector *connector,
+				      const struct drm_display_mode *mode,
+				      unsigned long long tmds_rate)
+{
+	return MODE_BAD;
+}
+
+static const struct drm_connector_hdmi_funcs reject_connector_hdmi_funcs = {
+	.tmds_char_rate_valid	= reject_connector_tmds_char_rate_valid,
+};
+
 static int dummy_connector_get_modes(struct drm_connector *connector)
 {
 	struct drm_atomic_helper_connector_hdmi_priv *priv =
@@ -493,7 +505,60 @@ static void drm_test_check_tmds_char_rate_rgb_12bpc(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, conn_state->hdmi.tmds_char_rate, preferred->clock * 1500);
 }
 
+/*
+ * Test that if we filter a rate through our hook, it's indeed rejected
+ * by the whole atomic_check logic.
+ *
+ * We do so by first doing a commit on the pipeline to make sure that it
+ * works, change the HDMI helpers pointer, and then try the same commit
+ * again to see if it fails as it should.
+ */
+static void drm_test_check_hdmi_funcs_reject_rate(struct kunit *test)
+{
+	struct drm_atomic_helper_connector_hdmi_priv *priv;
+	struct drm_modeset_acquire_ctx *ctx;
+	struct drm_atomic_state *state;
+	struct drm_display_mode *preferred;
+	struct drm_crtc_state *crtc_state;
+	struct drm_connector *conn;
+	struct drm_device *drm;
+	struct drm_crtc *crtc;
+	int ret;
+
+	priv = drm_atomic_helper_connector_hdmi_init(test,
+						     BIT(HDMI_COLORSPACE_RGB),
+						     8);
+	KUNIT_ASSERT_NOT_NULL(test, priv);
+
+	ctx = drm_kunit_helper_acquire_ctx_alloc(test);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
+
+	conn = &priv->connector;
+	preferred = find_preferred_mode(conn);
+	KUNIT_ASSERT_NOT_NULL(test, preferred);
+
+	drm = &priv->drm;
+	crtc = priv->crtc;
+	ret = light_up_connector(test, drm, crtc, conn, preferred, ctx);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	/* You shouldn't be doing that at home. */
+	conn->hdmi.funcs = &reject_connector_hdmi_funcs;
+
+	state = drm_kunit_helper_atomic_state_alloc(test, drm, ctx);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, state);
+
+	crtc_state = drm_atomic_get_crtc_state(state, crtc);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, crtc_state);
+
+	crtc_state->connectors_changed = true;
+
+	ret = drm_atomic_check_only(state);
+	KUNIT_EXPECT_LT(test, ret, 0);
+}
+
 static struct kunit_case drm_atomic_helper_connector_hdmi_check_tests[] = {
+	KUNIT_CASE(drm_test_check_hdmi_funcs_reject_rate),
 	KUNIT_CASE(drm_test_check_output_bpc_crtc_mode_changed),
 	KUNIT_CASE(drm_test_check_output_bpc_crtc_mode_not_changed),
 	KUNIT_CASE(drm_test_check_tmds_char_rate_rgb_8bpc),