drm/client: Add some tests for drm_connector_pick_cmdline_mode()

drm_connector_pick_cmdline_mode() is in charge of finding a proper
drm_display_mode from the definition we got in the video= command line
argument.

Let's add some unit tests to make sure we're not getting any regressions
there.
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v9-8-24b168e5bcd5@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/drm_client_modeset.c

@@ -1237,3 +1237,7 @@ int drm_client_modeset_dpms(struct drm_client_dev *client, int mode)
 	return ret;
 }
 EXPORT_SYMBOL(drm_client_modeset_dpms);
+
+#ifdef CONFIG_DRM_KUNIT_TEST
+#include "tests/drm_client_modeset_test.c"
+#endif

drivers/gpu/drm/tests/drm_client_modeset_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022 Maxime Ripard <mripard@kernel.org>
+ */
+
+#include <kunit/test.h>
+
+#include <drm/drm_connector.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_modes.h>
+#include <drm/drm_modeset_helper_vtables.h>
+#include <drm/drm_probe_helper.h>
+
+#include "drm_kunit_helpers.h"
+
+struct drm_client_modeset_test_priv {
+	struct drm_device *drm;
+	struct drm_connector connector;
+};
+
+static int drm_client_modeset_connector_get_modes(struct drm_connector *connector)
+{
+	return drm_add_modes_noedid(connector, 1920, 1200);
+}
+
+static const struct drm_connector_helper_funcs drm_client_modeset_connector_helper_funcs = {
+	.get_modes = drm_client_modeset_connector_get_modes,
+};
+
+static const struct drm_connector_funcs drm_client_modeset_connector_funcs = {
+};
+
+static int drm_client_modeset_test_init(struct kunit *test)
+{
+	struct drm_client_modeset_test_priv *priv;
+	int ret;
+
+	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, priv);
+
+	test->priv = priv;
+
+	priv->drm = drm_kunit_device_init(test, DRIVER_MODESET, "drm-client-modeset-test");
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv->drm);
+
+	ret = drmm_connector_init(priv->drm, &priv->connector,
+				  &drm_client_modeset_connector_funcs,
+				  DRM_MODE_CONNECTOR_Unknown,
+				  NULL);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	drm_connector_helper_add(&priv->connector, &drm_client_modeset_connector_helper_funcs);
+
+	return 0;
+
+}
+
+static void drm_test_pick_cmdline_res_1920_1080_60(struct kunit *test)
+{
+	struct drm_client_modeset_test_priv *priv = test->priv;
+	struct drm_device *drm = priv->drm;
+	struct drm_connector *connector = &priv->connector;
+	struct drm_cmdline_mode *cmdline_mode = &connector->cmdline_mode;
+	struct drm_display_mode *expected_mode, *mode;
+	const char *cmdline = "1920x1080@60";
+	int ret;
+
+	expected_mode = drm_mode_find_dmt(priv->drm, 1920, 1080, 60, false);
+	KUNIT_ASSERT_NOT_NULL(test, expected_mode);
+
+	KUNIT_ASSERT_TRUE(test,
+			  drm_mode_parse_command_line_for_connector(cmdline,
+								    connector,
+								    cmdline_mode));
+
+	mutex_lock(&drm->mode_config.mutex);
+	ret = drm_helper_probe_single_connector_modes(connector, 1920, 1080);
+	mutex_unlock(&drm->mode_config.mutex);
+	KUNIT_ASSERT_GT(test, ret, 0);
+
+	mode = drm_connector_pick_cmdline_mode(connector);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_EXPECT_TRUE(test, drm_mode_equal(expected_mode, mode));
+}
+
+
+static struct kunit_case drm_test_pick_cmdline_tests[] = {
+	KUNIT_CASE(drm_test_pick_cmdline_res_1920_1080_60),
+	{}
+};
+
+static struct kunit_suite drm_test_pick_cmdline_test_suite = {
+	.name = "drm_test_pick_cmdline",
+	.init = drm_client_modeset_test_init,
+	.test_cases = drm_test_pick_cmdline_tests
+};
+
+kunit_test_suite(drm_test_pick_cmdline_test_suite);