drm/i915/dp: Explicitly disable symbol scrambling while training

The DP spec says training patterns 1 and 2 are to be sent non-scrambled,
and the GPU docs claim that happens (or at least, there's no explicit
scrambling control).  But the sink may be confused if we don't
explicitly tell it what we're doing, so play it safe.
Signed-off-by: NAdam Jackson <ajax@redhat.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NKeith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1370,7 +1370,8 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
 			reg = DP | DP_LINK_TRAIN_PAT_1;
 
 		if (!intel_dp_set_link_train(intel_dp, reg,
-					     DP_TRAINING_PATTERN_1))
+					     DP_TRAINING_PATTERN_1 |
+					     DP_LINK_SCRAMBLING_DISABLE))
 			break;
 		/* Set training pattern 1 */
 
@@ -1445,7 +1446,8 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 
 		/* channel eq pattern */
 		if (!intel_dp_set_link_train(intel_dp, reg,
-					     DP_TRAINING_PATTERN_2))
+					     DP_TRAINING_PATTERN_2 |
+					     DP_LINK_SCRAMBLING_DISABLE))
 			break;
 
 		udelay(400);