drm/i915/dp: Add debugfs entry to force link retrain

Add a connector debugfs entry to force retrain an active link. This can
be used to test both custom link parameters (previously forced via the
force_link_rate/lane_count entries) or link train failure scenarios
(previously forced via the force_link_training_failure entry). The entry
will autoreset after the link-retrain is complete.

v2: Add the entry from intel_dp_link_training.c (Jani)
v3: Lock connection_mutex only for the required intel_dp state. (Ville)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610164933.2947366-21-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1777,6 +1777,7 @@ struct intel_dp {
 		/* Sequential link training failures after a passing LT */
 		int seq_train_failures;
 		int force_train_failure;
+		bool force_retrain;
 	} link;
 	bool reset_link_params;
 	int mso_link_count;

drivers/gpu/drm/i915/display/intel_dp.c

@@ -5065,7 +5065,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
 			drm_dp_mst_hpd_irq_send_new_request(&intel_dp->mst_mgr);
 	}
 
-	if (!link_ok)
+	if (!link_ok || intel_dp->link.force_retrain)
 		intel_encoder_link_check_queue_work(encoder, 0);
 
 	return !reprobe_needed;
@@ -5114,6 +5114,9 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
 	if (intel_psr_enabled(intel_dp))
 		return false;
 
+	if (intel_dp->link.force_retrain)
+		return true;
+
 	if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, DP_PHY_DPRX,
 					     link_status) < 0)
 		return false;
@@ -5252,8 +5255,9 @@ static int intel_dp_retrain_link(struct intel_encoder *encoder,
 	if (!intel_dp_needs_link_retrain(intel_dp))
 		return 0;
 
-	drm_dbg_kms(&dev_priv->drm, "[ENCODER:%d:%s] retraining link\n",
-		    encoder->base.base.id, encoder->base.name);
+	drm_dbg_kms(&dev_priv->drm, "[ENCODER:%d:%s] retraining link (forced %s)\n",
+		    encoder->base.base.id, encoder->base.name,
+		    str_yes_no(intel_dp->link.force_retrain));
 
 	for_each_intel_crtc_in_pipe_mask(&dev_priv->drm, crtc, pipe_mask) {
 		const struct intel_crtc_state *crtc_state =
@@ -5281,7 +5285,7 @@ static int intel_dp_retrain_link(struct intel_encoder *encoder,
 				    encoder->base.base.id, encoder->base.name,
 				    ERR_PTR(ret));
 
-		return ret;
+		goto out;
 	}
 
 	for_each_intel_crtc_in_pipe_mask(&dev_priv->drm, crtc, pipe_mask) {
@@ -5308,7 +5312,11 @@ static int intel_dp_retrain_link(struct intel_encoder *encoder,
 							      intel_crtc_pch_transcoder(crtc), true);
 	}
 
-	return 0;
+out:
+	if (ret != -EDEADLK)
+		intel_dp->link.force_retrain = false;
+
+	return ret;
 }
 
 void intel_dp_link_check(struct intel_encoder *encoder)

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -26,6 +26,7 @@
 #include "intel_dp.h"
 #include "intel_dp_link_training.h"
 #include "intel_encoder.h"
+#include "intel_hotplug.h"
 #include "intel_panel.h"
 
 #define LT_MSG_PREFIX			"[CONNECTOR:%d:%s][ENCODER:%d:%s][%s] "
@@ -1856,6 +1857,47 @@ DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_force_link_training_failure_fops,
 			 i915_dp_force_link_training_failure_show,
 			 i915_dp_force_link_training_failure_write, "%llu\n");
 
+static int i915_dp_force_link_retrain_show(void *data, u64 *val)
+{
+	struct intel_connector *connector = to_intel_connector(data);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int err;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	*val = intel_dp->link.force_retrain;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	return 0;
+}
+
+static int i915_dp_force_link_retrain_write(void *data, u64 val)
+{
+	struct intel_connector *connector = to_intel_connector(data);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int err;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	intel_dp->link.force_retrain = val;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	intel_hpd_trigger_irq(dp_to_dig_port(intel_dp));
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_force_link_retrain_fops,
+			 i915_dp_force_link_retrain_show,
+			 i915_dp_force_link_retrain_write, "%llu\n");
+
 void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
 {
 	struct dentry *root = connector->base.debugfs_entry;
@@ -1878,4 +1920,7 @@ void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
 
 	debugfs_create_file("i915_dp_force_link_training_failure", 0644, root,
 			    connector, &i915_dp_force_link_training_failure_fops);
+
+	debugfs_create_file("i915_dp_force_link_retrain", 0644, root,
+			    connector, &i915_dp_force_link_retrain_fops);
 }