[PATCH i-g-t 05/13] tests/intel/kms_dp_link_training: use the lowest pixel clock mode

[Kunal Joshi <kunal1.joshi@intel.com>]

The preferred mode of a modern monitor may need most of the link
bandwidth, leaving the lower link configs unusable. Use the mode with
the lowest pixel clock instead, so that as many configs as possible can
carry it. This should also keep DSC out of the picture.

The override is cleared by igt_display_reset(), so there's no need to
clean up.

This prepares for training all the allowed link configs.

Assisted-by: GitHub_Copilot:claude-opus-5
Signed-off-by: Kunal Joshi <kunal1.joshi@intel.com>
Reviewed-by: Sowmiya S <sowmiya.s@intel.com>
---
 tests/intel/kms_dp_link_training.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tests/intel/kms_dp_link_training.c b/tests/intel/kms_dp_link_training.c
index 8d079ffb0..76bbe3733 100644
--- a/tests/intel/kms_dp_link_training.c
+++ b/tests/intel/kms_dp_link_training.c
@@ -185,6 +185,25 @@ static void train_link_config(data_t *data, bool mst,
 	assert_link_retrain_not_disabled(data, config);
 }
 
+/*
+ * override_lowest_mode - Drive the mode with the lowest pixel clock, so that
+ * the largest number of link configurations can carry it.
+ */
+static void override_lowest_mode(data_t *data, igt_output_t *output)
+{
+	drmModeConnector *connector = output->config.connector;
+	drmModeModeInfo *mode = NULL;
+	int i;
+
+	for (i = 0; i < connector->count_modes; i++)
+		if (!mode || connector->modes[i].clock < mode->clock)
+			mode = &connector->modes[i];
+
+	igt_assert_f(mode, "No mode on output %s\n", igt_output_name(output));
+
+	igt_output_override_mode(output, mode);
+}
+
 /*
  * setup_planes_fbs - Create solid-color FBs and attach them to the primary plane.
  */
@@ -224,6 +243,7 @@ static void do_modeset(data_t *data, bool mst)
 	int n_pipes = 0;
 	int out_count = 0;
 	igt_crtc_t *crtc;
+	int i;
 
 	for_each_crtc(&data->display, crtc) {
 		valid_pipes_mask |= BIT(crtc->hardware_pipe);
@@ -243,6 +263,9 @@ static void do_modeset(data_t *data, bool mst)
 
 	igt_assert_f(out_count > 0, "Require at least one output\n");
 
+	for (i = 0; i < out_count; i++)
+		override_lowest_mode(data, outs[i]);
+
 	igt_set_all_master_pipes_for_platform(&data->display, &master_pipes_mask);
 
 	igt_assert_f(igt_assign_pipes_for_outputs(data->drm_fd,
-- 
2.25.1