drm/i915: Fix broken mst get_hw_state.

connector->encoder is initialized as NULL. Fix this by setting it in
during pre enable. MST connectors are not read out during initial hw
readout, and have no fixed encoder mappings. So it's harmless to
return false when the connector has never been assigned to an encoder.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -6305,7 +6305,7 @@ static void intel_connector_check_state(struct intel_connector *connector)
 		      connector->base.name);
 
 	if (connector->get_hw_state(connector)) {
-		struct drm_encoder *encoder = &connector->encoder->base;
+		struct intel_encoder *encoder = connector->encoder;
 		struct drm_connector_state *conn_state = connector->base.state;
 
 		I915_STATE_WARN(!crtc,
@@ -6317,13 +6317,13 @@ static void intel_connector_check_state(struct intel_connector *connector)
 		I915_STATE_WARN(!crtc->state->active,
 		      "connector is active, but attached crtc isn't\n");
 
-		if (!encoder)
+		if (!encoder || encoder->type == INTEL_OUTPUT_DP_MST)
 			return;
 
-		I915_STATE_WARN(conn_state->best_encoder != encoder,
+		I915_STATE_WARN(conn_state->best_encoder != &encoder->base,
 			"atomic encoder doesn't match attached encoder\n");
 
-		I915_STATE_WARN(conn_state->crtc != encoder->crtc,
+		I915_STATE_WARN(conn_state->crtc != encoder->base.crtc,
 			"attached encoder crtc differs from connector crtc\n");
 	} else {
 		I915_STATE_WARN(crtc && crtc->state->active,

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -173,6 +173,11 @@ static void intel_mst_pre_enable_dp(struct intel_encoder *encoder)
 		return;
 	}
 
+	/* MST encoders are bound to a crtc, not to a connector,
+	 * force the mapping here for get_hw_state.
+	 */
+	found->encoder = encoder;
+
 	DRM_DEBUG_KMS("%d\n", intel_dp->active_mst_links);
 	intel_mst->port = found->port;
 
@@ -400,7 +405,7 @@ static const struct drm_encoder_funcs intel_dp_mst_enc_funcs = {
 
 static bool intel_dp_mst_get_hw_state(struct intel_connector *connector)
 {
-	if (connector->encoder) {
+	if (connector->encoder && connector->base.state->crtc) {
 		enum pipe pipe;
 		if (!connector->encoder->get_hw_state(connector->encoder, &pipe))
 			return false;