[PATCH i-g-t 05/13] tests/intel/kms_dp_link_training: Drive the smallest mode the sink offers

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

The test modesets the output's preferred mode, which on a modern
monitor needs most of the link. The driver picks the lowest
configuration that carries the mode, so a large mode leaves most of the
link configurations below the threshold where they can be used at all.

Override the smallest mode the sink offers instead. That keeps the
largest number of configurations usable, and it stays out of the
compressed regime, where the bpp the driver picks rather than the link
configuration absorbs the difference.

The override is cleared by the igt_display_reset() each run starts
with, so it needs no explicit teardown.

Prep for training every allowed configuration.

Assisted-by: GitHub_Copilot:claude-opus-5
Signed-off-by: Kunal Joshi <kunal1.joshi@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 b2d686f28..6a174da88 100644
--- a/tests/intel/kms_dp_link_training.c
+++ b/tests/intel/kms_dp_link_training.c
@@ -183,6 +183,25 @@ static void train_link_config(data_t *data, bool mst,
 	assert_link_recovery_idle(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.
  */
@@ -222,6 +241,7 @@ 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);
@@ -241,6 +261,9 @@ 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