[PATCH 1/2] drm/i915/dp: Fix error handling during 128b/132b link training

[Imre Deak]

At the end of a 128b/132b link training sequence, the HW expects the
transcoder training pattern to be set to TPS2 and from that to normal
mode (disabling the training pattern). Transitioning from TPS1 directly
to normal mode leaves the transcoder in a stuck state, resulting in
page-flip timeouts later in the modeset sequence.

Atm, in case of a failure during link training, the transcoder may be
still set to output the TPS1 pattern. Later the transcoder is then set
from TPS1 directly to normal mode in intel_dp_stop_link_train(), leading
to modeset failures later as described above. Fix this by setting the
training patter to TPS2, if the link training failed at any point.

Cc: stable at vger.kernel.org # v5.18+
Cc: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 .../gpu/drm/i915/display/intel_dp_link_training.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

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 3cc06c916017d..11953b03bb6aa 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -1563,7 +1563,7 @@ intel_dp_128b132b_link_train(struct intel_dp *intel_dp,
 
 	if (wait_for(intel_dp_128b132b_intra_hop(intel_dp, crtc_state) == 0, 500)) {
 		lt_err(intel_dp, DP_PHY_DPRX, "128b/132b intra-hop not clear\n");
-		return false;
+		goto out;
 	}
 
 	if (intel_dp_128b132b_lane_eq(intel_dp, crtc_state) &&
@@ -1575,6 +1575,19 @@ intel_dp_128b132b_link_train(struct intel_dp *intel_dp,
 	       passed ? "passed" : "failed",
 	       crtc_state->port_clock, crtc_state->lane_count);
 
+out:
+	/*
+	 * Ensure that the training pattern does get set to TPS2 even in case
+	 * of a failure, as is the case at the end of a passing link training
+	 * and what is expected by the transcoder. Leaving TPS1 set (and
+	 * disabling the link train mode in DP_TP_CTL later from TPS1 directly)
+	 * would result in a stuck transcoder HW state and flip-done timeouts
+	 * later in the modeset sequence.
+	 */
+	if (!passed)
+		intel_dp_program_link_training_pattern(intel_dp, crtc_state,
+						       DP_PHY_DPRX, DP_TRAINING_PATTERN_2);
+
 	return passed;
 }
 
-- 
2.44.2