[PATCH 012/108] drm/i915/dp_link_training: Prevent repeated autoretrain attempts

[Imre Deak <imre.deak@intel.com>]

After a regular modeset link training failure, the driver attempts to
recover the link via an autoretrain using the same link parameters as
the modeset.

If the autoretrain fails as well, the set of allowed link configurations
is reduced via a fallback mechanism. For further link training, the
modeset parameters will likely need to change. This lowers the required
link bandwidth and allows selecting a link configuration from the
fallback-reduced set. Only userspace can perform such a modeset change.
Therefore, the driver notifies userspace to take over link recovery.

Userspace is expected to continue with the recovery attempt via a
modeset with updated parameters. The driver must not interfere with
these modesets.

link_training->seq_train_failures is set to MAX_SEQ_TRAIN_FAILURES after
the autoretrain fails. If a fallback selection also fails after this,
as no link configurations remain, retrain_disabled is set as well.

retrain_disabled is therefore somewhat misnamed: it indicates that no
fallback is available, not that autoretraining is disabled. This will be
addressed in a follow-up change by renaming the flag. For now, prevent
further autoretrain attempts based on the correct condition:
seq_train_failures == MAX_SEQ_TRAIN_FAILURES.

This also prepares for replacing the counter with an enum in a follow-up
change.

Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_link_training.c | 2 +-
 1 file changed, 1 insertion(+), 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 db1e03c15596d..54f506bbd6d1d 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -1987,7 +1987,7 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
 					intel_dp->lane_count))
 		return false;
 
-	if (link_training->retrain_disabled)
+	if (link_training->seq_train_failures >= MAX_SEQ_TRAIN_FAILURES)
 		return false;
 
 	if (link_training->seq_train_failures)
-- 
2.49.1