[PATCH v2 14/21] drm/i915/dp: Disable link retraining after the last fallback step

[Imre Deak]

After a link training failure if the link parameters can't be further
reduced, there is no point in trying to retrain the link in the driver.
This avoids excessive retrain attempts after detecting a bad link, for
instance while handling MST HPD IRQs, which is likely redundant as the
link training failed already twice with the same minimum link
parameters. Userspace can still try to retrain the link with these
parameters via a modeset.

While at it make the error message more accurate and emit instead a
debug message if the link training failure was only forced for testing
purposes.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_dp.c       |  4 ++++
 .../drm/i915/display/intel_dp_link_training.c | 22 +++++++++++++------
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index bde518c843468..eb0cac3e27acf 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -1765,6 +1765,7 @@ struct intel_dp {
 		int max_lane_count;
 		/* Max rate for the current link */
 		int max_rate;
+		bool retrain_disabled;
 		/* Sequential link training failures after a passing LT */
 		int seq_train_failures;
 	} link;
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index b72dbd7becb74..34d64fe3302ef 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2950,6 +2950,7 @@ static void intel_dp_reset_link_params(struct intel_dp *intel_dp)
 {
 	intel_dp->link.max_lane_count = intel_dp_max_common_lane_count(intel_dp);
 	intel_dp->link.max_rate = intel_dp_max_common_rate(intel_dp);
+	intel_dp->link.retrain_disabled = false;
 	intel_dp->link.seq_train_failures = 0;
 }
 
@@ -5061,6 +5062,9 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
 					intel_dp->lane_count))
 		return false;
 
+	if (intel_dp->link.retrain_disabled)
+		return false;
+
 	if (intel_dp->link.seq_train_failures)
 		return true;
 
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 97d499e4b6ef7..375f59afd4dec 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -1165,10 +1165,8 @@ static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
 		new_link_rate = intel_dp_max_common_rate(intel_dp);
 	}
 
-	if (new_lane_count < 0) {
-		drm_err(&i915->drm, "Link Training Unsuccessful\n");
+	if (new_lane_count < 0)
 		return -1;
-	}
 
 	if (intel_dp_is_edp(intel_dp) &&
 	    !intel_dp_can_link_train_fallback_for_edp(intel_dp, new_link_rate, new_lane_count)) {
@@ -1187,7 +1185,7 @@ static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
 	return 0;
 }
 
-static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *state,
+static bool intel_dp_schedule_fallback_link_training(struct intel_atomic_state *state,
 						     struct intel_dp *intel_dp,
 						     const struct intel_crtc_state *crtc_state)
 {
@@ -1195,7 +1193,7 @@ static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *
 
 	if (!intel_digital_port_connected(&dp_to_dig_port(intel_dp)->base)) {
 		lt_dbg(intel_dp, DP_PHY_DPRX, "Link Training failed on disconnected sink.\n");
-		return;
+		return true;
 	}
 
 	if (intel_dp->hobl_active) {
@@ -1203,11 +1201,13 @@ static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *
 		       "Link Training failed with HOBL active, not enabling it from now on\n");
 		intel_dp->hobl_failed = true;
 	} else if (intel_dp_get_link_train_fallback_values(intel_dp, crtc_state)) {
-		return;
+		return false;
 	}
 
 	/* Schedule a Hotplug Uevent to userspace to start modeset */
 	intel_dp_queue_modeset_retry_for_link(state, encoder, crtc_state);
+
+	return true;
 }
 
 /* Perform the link training on all LTTPRs and the DPRX on a link. */
@@ -1518,7 +1518,15 @@ void intel_dp_start_link_train(struct intel_atomic_state *state,
 		return;
 	}
 
-	intel_dp_schedule_fallback_link_training(state, intel_dp, crtc_state);
+	if (intel_dp_schedule_fallback_link_training(state, intel_dp, crtc_state))
+		return;
+
+	intel_dp->link.retrain_disabled = true;
+
+	if (!passed)
+		lt_err(intel_dp, DP_PHY_DPRX, "Can't reduce link training parameters after failure\n");
+	else
+		lt_dbg(intel_dp, DP_PHY_DPRX, "Can't reduce link training parameters after forced failure\n");
 }
 
 void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
-- 
2.43.3