drm/i915/dp: Disable FEC ready flag in the sink

Disable the FEC ready flag in the sink during a disabling modeset.
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030155843.2251023-21-imre.deak@intel.com

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

@@ -2211,18 +2211,21 @@ static void intel_dp_sink_set_msa_timing_par_ignore_state(struct intel_dp *intel
 }
 
 static void intel_dp_sink_set_fec_ready(struct intel_dp *intel_dp,
-					const struct intel_crtc_state *crtc_state)
+					const struct intel_crtc_state *crtc_state,
+					bool enable)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 
 	if (!crtc_state->fec_enable)
 		return;
 
-	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_FEC_CONFIGURATION, DP_FEC_READY) <= 0)
-		drm_dbg_kms(&i915->drm,
-			    "Failed to set FEC_READY in the sink\n");
+	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_FEC_CONFIGURATION,
+			       enable ? DP_FEC_READY : 0) <= 0)
+		drm_dbg_kms(&i915->drm, "Failed to set FEC_READY to %s in the sink\n",
+			    enable ? "enabled" : "disabled");
 
-	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_FEC_STATUS,
+	if (enable &&
+	    drm_dp_dpcd_writeb(&intel_dp->aux, DP_FEC_STATUS,
 			       DP_FEC_DECODE_EN_DETECTED | DP_FEC_DECODE_DIS_DETECTED) <= 0)
 		drm_dbg_kms(&i915->drm, "Failed to clear FEC detected flags\n");
 }
@@ -2541,7 +2544,7 @@ static void mtl_ddi_pre_enable_dp(struct intel_atomic_state *state,
 	 * in the FEC_CONFIGURATION register to 1 before initiating link
 	 * training
 	 */
-	intel_dp_sink_set_fec_ready(intel_dp, crtc_state);
+	intel_dp_sink_set_fec_ready(intel_dp, crtc_state, true);
 
 	intel_dp_check_frl_training(intel_dp);
 	intel_dp_pcon_dsc_configure(intel_dp, crtc_state);
@@ -2692,7 +2695,7 @@ static void tgl_ddi_pre_enable_dp(struct intel_atomic_state *state,
 	 * in the FEC_CONFIGURATION register to 1 before initiating link
 	 * training
 	 */
-	intel_dp_sink_set_fec_ready(intel_dp, crtc_state);
+	intel_dp_sink_set_fec_ready(intel_dp, crtc_state, true);
 
 	intel_dp_check_frl_training(intel_dp);
 	intel_dp_pcon_dsc_configure(intel_dp, crtc_state);
@@ -2768,7 +2771,7 @@ static void hsw_ddi_pre_enable_dp(struct intel_atomic_state *state,
 	intel_dp_configure_protocol_converter(intel_dp, crtc_state);
 	intel_dp_sink_set_decompression_state(intel_dp, crtc_state,
 					      true);
-	intel_dp_sink_set_fec_ready(intel_dp, crtc_state);
+	intel_dp_sink_set_fec_ready(intel_dp, crtc_state, true);
 	intel_dp_start_link_train(intel_dp, crtc_state);
 	if ((port != PORT_A || DISPLAY_VER(dev_priv) >= 9) &&
 	    !is_trans_port_sync_mode(crtc_state))
@@ -2997,6 +3000,8 @@ static void intel_ddi_post_disable_dp(struct intel_atomic_state *state,
 
 	intel_disable_ddi_buf(encoder, old_crtc_state);
 
+	intel_dp_sink_set_fec_ready(intel_dp, old_crtc_state, false);
+
 	/*
 	 * From TGL spec: "If single stream or multi-stream master transcoder:
 	 * Configure Transcoder Clock select to direct no clock to the