[PATCH 4.6 201/203] drm/i915: Revert DisplayPort fast link training feature

[Greg Kroah-Hartman]

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mika Kahola <mika.kahola@xxxxxxxxx>

commit 34511dce4b35685d3988d5c8b100d11a068db5bd upstream.

It has been found out that in some HW combination the DisplayPort
fast link training feature caused screen flickering. Let's revert
this feature for now until we can ensure that the feature works for
all platforms.

This is a manual revert of commits 5fa836a9d859 ("drm/i915: DP link
training optimization") and 4e96c97742f4 ("drm/i915: eDP link training
optimization").

Fixes: 5fa836a9d859 ("drm/i915: DP link training optimization")
Fixes: 4e96c97742f4 ("drm/i915: eDP link training optimization")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Mika Kahola <mika.kahola@xxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/1466410226-19543-1-git-send-email-mika.kahola@xxxxxxxxx
(cherry picked from commit 91df09d92ad82c8778ca218097bf827f154292ca)
Signed-off-by: Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/intel_dp.c               |    3 ---
 drivers/gpu/drm/i915/intel_dp_link_training.c |   25 ++-----------------------
 drivers/gpu/drm/i915/intel_drv.h              |    2 --
 3 files changed, 2 insertions(+), 28 deletions(-)

--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -5022,9 +5022,6 @@ intel_dp_hpd_pulse(struct intel_digital_
 	intel_display_power_get(dev_priv, power_domain);
 
 	if (long_hpd) {
-		/* indicate that we need to restart link training */
-		intel_dp->train_set_valid = false;
-
 		if (!intel_digital_port_connected(dev_priv, intel_dig_port))
 			goto mst_fail;
 
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -85,8 +85,7 @@ static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
-	if (!intel_dp->train_set_valid)
-		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
+	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
 	intel_dp_set_signal_levels(intel_dp);
 	return intel_dp_set_link_train(intel_dp, dp_train_pat);
 }
@@ -161,22 +160,6 @@ intel_dp_link_training_clock_recovery(st
 			break;
 		}
 
-		/*
-		 * if we used previously trained voltage and pre-emphasis values
-		 * and we don't get clock recovery, reset link training values
-		 */
-		if (intel_dp->train_set_valid) {
-			DRM_DEBUG_KMS("clock recovery not ok, reset");
-			/* clear the flag as we are not reusing train set */
-			intel_dp->train_set_valid = false;
-			if (!intel_dp_reset_link_train(intel_dp,
-						       DP_TRAINING_PATTERN_1 |
-						       DP_LINK_SCRAMBLING_DISABLE)) {
-				DRM_ERROR("failed to enable link training\n");
-				return;
-			}
-			continue;
-		}
 
 		/* Check to see if we've tried the max voltage */
 		for (i = 0; i < intel_dp->lane_count; i++)
@@ -284,7 +267,6 @@ intel_dp_link_training_channel_equalizat
 		/* Make sure clock is still ok */
 		if (!drm_dp_clock_recovery_ok(link_status,
 					      intel_dp->lane_count)) {
-			intel_dp->train_set_valid = false;
 			intel_dp_link_training_clock_recovery(intel_dp);
 			intel_dp_set_link_train(intel_dp,
 						training_pattern |
@@ -301,7 +283,6 @@ intel_dp_link_training_channel_equalizat
 
 		/* Try 5 times, then try clock recovery if that fails */
 		if (tries > 5) {
-			intel_dp->train_set_valid = false;
 			intel_dp_link_training_clock_recovery(intel_dp);
 			intel_dp_set_link_train(intel_dp,
 						training_pattern |
@@ -322,10 +303,8 @@ intel_dp_link_training_channel_equalizat
 
 	intel_dp_set_idle_link_train(intel_dp);
 
-	if (channel_eq) {
-		intel_dp->train_set_valid = true;
+	if (channel_eq)
 		DRM_DEBUG_KMS("Channel EQ done. DP Training successful\n");
-	}
 }
 
 void intel_dp_stop_link_train(struct intel_dp *intel_dp)
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -811,8 +811,6 @@ struct intel_dp {
 	/* This is called before a link training is starterd */
 	void (*prepare_link_retrain)(struct intel_dp *intel_dp);
 
-	bool train_set_valid;
-
 	/* Displayport compliance testing */
 	unsigned long compliance_test_type;
 	unsigned long compliance_test_data;