Revert "drm/i915: Try harder to complete DP training pattern 1"

This reverts commit 2477367083b3eaa97f87993ab26627a02f350551.

If (for whatever reason) the DP sink device never asks for the maximal
voltage level, we never don't hit the check that should bail us out
after 5 retries of the same voltage. Which leads to an endless loop in
the DP link training code, which hangs the driver.

Now some more DP link training experiments on eDP panels seem to
indicate that our training algorithm isn't robust enough anyway and
needs more work. Hence for 3.7-fixes, let's just revert the regressing
commit instead of trying to apply more duct-tape.

Reported-by: Oleksij Rempel <bug-track@fisher-privat.net>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index bd2c34a..e37ca2c 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1798,7 +1798,8 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
                        if ((intel_dp->train_set[i] & DP_TRAIN_MAX_SWING_REACHED) == 0)
                                break;
                if (i == intel_dp->lane_count && voltage_tries == 5) {
-                       if (++loop_tries == 5) {
+                       ++loop_tries;
+                       if (loop_tries == 5) {
                                DRM_DEBUG_KMS("too many full retries, give up\n");
                                break;
                        }
@@ -1808,11 +1809,15 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
                }
 
                /* 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 = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;
-                       voltage_tries = 0;
-               } else
+               if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) == voltage) {
                        ++voltage_tries;
+                       if (voltage_tries == 5) {
+                               DRM_DEBUG_KMS("too many voltage retries, give up\n");
+                               break;
+                       }
+               } else
+                       voltage_tries = 0;
+               voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;
 
                /* Compute new intel_dp->train_set as requested by target */
                intel_get_adjust_train(intel_dp, link_status);