drm/i915/dp: Have intel_dp_get_adjust_train() tell us if anything changed

In order to implement the POST_LT_ADJ_REQ sequence we need to
know whether the sink actually requested a changed to the
vswing/pre-emph values.

Tested-by: Imre Deak <[e-mail]>
Reviewed-by: Imre Deak <[e-mail]>
Signed-off-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/display/intel_dp_link_training.c

···
 	_TRAIN_REQ_TX_FFE_ARGS(link_status, 2), \
 	_TRAIN_REQ_TX_FFE_ARGS(link_status, 3)
 
-void
+bool
 intel_dp_get_adjust_train(struct intel_dp *intel_dp,
 			  const struct intel_crtc_state *crtc_state,
 			  enum drm_dp_phy dp_phy,
 			  const u8 link_status[DP_LINK_STATUS_SIZE])
 {
+	bool changed = false;
 	int lane;
 
 	if (intel_dp_is_uhbr(crtc_state)) {
···
 		       TRAIN_REQ_PREEMPH_ARGS(link_status));
 	}
 
-	for (lane = 0; lane < 4; lane++)
-		intel_dp->train_set[lane] =
-			intel_dp_get_lane_adjust_train(intel_dp, crtc_state,
-						       dp_phy, link_status, lane);
+	for (lane = 0; lane < 4; lane++) {
+		u8 new = intel_dp_get_lane_adjust_train(intel_dp, crtc_state,
+							dp_phy, link_status, lane);
+		if (intel_dp->train_set[lane] == new)
+			continue;
+
+		intel_dp->train_set[lane] = new;
+		changed = true;
+	}
+
+	return changed;
 }
 
 static int intel_dp_training_pattern_set_reg(struct intel_dp *intel_dp,

drivers/gpu/drm/i915/display/intel_dp_link_training.h

···
 				   int link_bw, int rate_select, int lane_count,
 				   bool enhanced_framing);
 
-void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
+bool intel_dp_get_adjust_train(struct intel_dp *intel_dp,
 			       const struct intel_crtc_state *crtc_state,
 			       enum drm_dp_phy dp_phy,
 			       const u8 link_status[DP_LINK_STATUS_SIZE]);