drm/dp/i915: Make clock recovery in the link training compliant with DP Spec 1.2

This function cleans up clock recovery loop in link training compliant
tp Dp Spec 1.2. It tries the clock recovery 5 times for the same voltage
or until max voltage swing is reached and removes the additional non
compliant retries. This function now returns a boolean values based on
if clock recovery passed or failed.

v3:
* Better Debug prints in case of failures (Mika Kahola)
v2:
* Rebased on top of new revision of vswing patch (Manasi Navare)

Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/intel_dp_link_training.c

@@ -125,12 +125,11 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 }
 
 /* Enable corresponding port and start training pattern 1 */
-static void
+static bool
 intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 {
-	int i;
 	uint8_t voltage;
-	int voltage_tries, loop_tries;
+	int voltage_tries, max_vswing_tries;
 	uint8_t link_config[2];
 	uint8_t link_bw, rate_select;
 
@@ -146,6 +145,7 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 	if (drm_dp_enhanced_frame_cap(intel_dp->dpcd))
 		link_config[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
 	drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_BW_SET, link_config, 2);
+
 	if (intel_dp->num_sink_rates)
 		drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_RATE_SET,
 				  &rate_select, 1);
@@ -161,58 +161,54 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 				       DP_TRAINING_PATTERN_1 |
 				       DP_LINK_SCRAMBLING_DISABLE)) {
 		DRM_ERROR("failed to enable link training\n");
-		return;
+		return false;
 	}
 
-	voltage = 0xff;
-	voltage_tries = 0;
-	loop_tries = 0;
+	voltage_tries = 1;
+	max_vswing_tries = 0;
 	for (;;) {
 		uint8_t link_status[DP_LINK_STATUS_SIZE];
 
 		drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);
+
 		if (!intel_dp_get_link_status(intel_dp, link_status)) {
 			DRM_ERROR("failed to get link status\n");
-			break;
+			return false;
 		}
 
 		if (drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)) {
 			DRM_DEBUG_KMS("clock recovery OK\n");
-			break;
+			return true;
 		}
 
-		/* Check to see if we've tried the max voltage */
-		if (intel_dp_link_max_vswing_reached(intel_dp)) {
-			++loop_tries;
-			if (loop_tries == 5) {
-				DRM_ERROR("too many full retries, give up\n");
-				intel_dp_dump_link_status(link_status);
-				break;
-			}
-			intel_dp_reset_link_train(intel_dp,
-						  DP_TRAINING_PATTERN_1 |
-						  DP_LINK_SCRAMBLING_DISABLE);
-			voltage_tries = 0;
-			continue;
+		if (voltage_tries == 5) {
+			DRM_DEBUG_KMS("Same voltage tried 5 times\n");
+			return false;
+		}
+
+		if (max_vswing_tries == 1) {
+			DRM_DEBUG_KMS("Max Voltage Swing reached\n");
+			return false;
 		}
 
-		/* Check to see if we've tried the same voltage 5 times */
-		if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) == voltage) {
-			++voltage_tries;
-			if (voltage_tries == 5) {
-				DRM_ERROR("too many voltage retries, give up\n");
-				break;
-			}
-		} else
-			voltage_tries = 0;
 		voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;
 
 		/* Update training set as requested by target */
 		intel_get_adjust_train(intel_dp, link_status);
 		if (!intel_dp_update_link_train(intel_dp)) {
 			DRM_ERROR("failed to update link training\n");
-			break;
+			return false;
 		}
+
+		if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) ==
+		    voltage)
+			++voltage_tries;
+		else
+			voltage_tries = 1;
+
+		if (intel_dp_link_max_vswing_reached(intel_dp))
+			++max_vswing_tries;
+
 	}
 }