[Intel-gfx] [PATCH 3/7] drm/i915: Simplify the link training functions

[Imre Deak]

Split the prepare, link training, fallback-handling steps into their own
functions for clarity and as a preparation for the upcoming LTTPR changes.

While at it also add some documentation to exported functions.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 .../drm/i915/display/intel_dp_link_training.c | 80 ++++++++++++++-----
 1 file changed, 62 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
index 6d13d00db5e6..0c3809891bd2 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -162,14 +162,13 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 	return true;
 }
 
-/* Enable corresponding port and start training pattern 1 */
-static bool
-intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
+/*
+ * Prepare link training by configuring the link parameters and enabling the
+ * corresponding port.
+ */
+static void intel_dp_prepare_link_train(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-	u8 voltage;
-	int voltage_tries, cr_tries, max_cr_tries;
-	bool max_vswing_reached = false;
 	u8 link_config[2];
 	u8 link_bw, rate_select;
 
@@ -203,6 +202,16 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 	drm_dp_dpcd_write(&intel_dp->aux, DP_DOWNSPREAD_CTRL, link_config, 2);
 
 	intel_dp->DP |= DP_PORT_EN;
+}
+
+/* Perform the link training clock recovery phase using training pattern 1. */
+static bool
+intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
+{
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	u8 voltage;
+	int voltage_tries, cr_tries, max_cr_tries;
+	bool max_vswing_reached = false;
 
 	/* clock recovery */
 	if (!intel_dp_reset_link_train(intel_dp,
@@ -325,6 +334,10 @@ static u32 intel_dp_training_pattern(struct intel_dp *intel_dp)
 	return DP_TRAINING_PATTERN_2;
 }
 
+/*
+ * Perform the link training channel equalization phase using one of training
+ * pattern 2, 3 or 4 depending on the the source and sink capabilities.
+ */
 static bool
 intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
 {
@@ -395,6 +408,15 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
 
 }
 
+/**
+ * intel_dp_stop_link_train - stop link training
+ * @intel_dp: DP struct
+ *
+ * Stop the link training of the @intel_dp port, programming the port to
+ * output an idle pattern on the link and  disabling the training pattern in
+ * the sink's DPCD.
+ * This function must be called after intel_dp_start_link_train().
+ */
 void intel_dp_stop_link_train(struct intel_dp *intel_dp)
 {
 	intel_dp->link_trained = true;
@@ -403,30 +425,37 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp)
 				DP_TRAINING_PATTERN_DISABLE);
 }
 
-void
-intel_dp_start_link_train(struct intel_dp *intel_dp)
+static bool
+intel_dp_link_train(struct intel_dp *intel_dp)
 {
 	struct intel_connector *intel_connector = intel_dp->attached_connector;
+	bool ret = false;
+
+	intel_dp_prepare_link_train(intel_dp);
 
 	if (!intel_dp_link_training_clock_recovery(intel_dp))
-		goto failure_handling;
+		goto out;
+
 	if (!intel_dp_link_training_channel_equalization(intel_dp))
-		goto failure_handling;
+		goto out;
 
-	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
-		    "[CONNECTOR:%d:%s] Link Training Passed at Link Rate = %d, Lane count = %d",
-		    intel_connector->base.base.id,
-		    intel_connector->base.name,
-		    intel_dp->link_rate, intel_dp->lane_count);
-	return;
+	ret = true;
 
- failure_handling:
+out:
 	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
-		    "[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
+		    "[CONNECTOR:%d:%s] Link Training %s at Link Rate = %d, Lane count = %d",
 		    intel_connector->base.base.id,
 		    intel_connector->base.name,
+		    ret ? "passed" : "failed",
 		    intel_dp->link_rate, intel_dp->lane_count);
 
+	return ret;
+}
+
+static void intel_dp_schedule_fallback_link_training(struct intel_dp *intel_dp)
+{
+	struct intel_connector *intel_connector = intel_dp->attached_connector;
+
 	if (intel_dp->hobl_active) {
 		drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 			    "Link Training failed with HOBL active, not enabling it from now on");
@@ -440,3 +469,18 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
 	/* Schedule a Hotplug Uevent to userspace to start modeset */
 	schedule_work(&intel_connector->modeset_retry_work);
 }
+
+/**
+ * intel_dp_start_link_train - start link training
+ * @intel_dp: DP struct
+ *
+ * Start the link training of the @intel_dp port, scheduling a fallback
+ * retraining with reduced link rate/lane parameters if the link training
+ * fails.
+ * After calling this function intel_dp_stop_link_train() must be called.
+ */
+void intel_dp_start_link_train(struct intel_dp *intel_dp)
+{
+	if (!intel_dp_link_train(intel_dp))
+		intel_dp_schedule_fallback_link_training(intel_dp);
+}
-- 
2.17.1