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

This reverts commit 24773670.

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: NOleksij Rempel <bug-track@fisher-privat.net>
Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

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);