drm/mst: read sideband messaging cap

Amend drm_dp_read_mst_cap() to return an enum, indicating "SST", "SST
with sideband messaging", or "MST". Modify all call sites to take the
new return value into account.

v2:
- Rename enumerators (Ville)

Cc: Arun R Murthy <arun.r.murthy@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b32a3704934871a67d06420b760e148b76c5ced8.1710839496.git.jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -3608,24 +3608,30 @@ fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
 EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
 
 /**
- * drm_dp_read_mst_cap() - check whether or not a sink supports MST
+ * drm_dp_read_mst_cap() - Read the sink's MST mode capability
  * @aux: The DP AUX channel to use
  * @dpcd: A cached copy of the DPCD capabilities for this sink
  *
- * Returns: %True if the sink supports MST, %false otherwise
+ * Returns: enum drm_dp_mst_mode to indicate MST mode capability
  */
-bool drm_dp_read_mst_cap(struct drm_dp_aux *aux,
-			 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+enum drm_dp_mst_mode drm_dp_read_mst_cap(struct drm_dp_aux *aux,
+					 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {
 	u8 mstm_cap;
 
 	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_12)
-		return false;
+		return DRM_DP_SST;
 
 	if (drm_dp_dpcd_readb(aux, DP_MSTM_CAP, &mstm_cap) != 1)
-		return false;
+		return DRM_DP_SST;
+
+	if (mstm_cap & DP_MST_CAP)
+		return DRM_DP_MST;
+
+	if (mstm_cap & DP_SINGLE_STREAM_SIDEBAND_MSG)
+		return DRM_DP_SST_SIDEBAND_MSG;
 
-	return mstm_cap & DP_MST_CAP;
+	return DRM_DP_SST;
 }
 EXPORT_SYMBOL(drm_dp_read_mst_cap);
 

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

@@ -4046,7 +4046,7 @@ intel_dp_can_mst(struct intel_dp *intel_dp)
 
 	return i915->display.params.enable_dp_mst &&
 		intel_dp_mst_source_support(intel_dp) &&
-		drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd);
+		drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DRM_DP_MST;
 }
 
 static void
@@ -4055,7 +4055,7 @@ intel_dp_configure_mst(struct intel_dp *intel_dp)
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	struct intel_encoder *encoder =
 		&dp_to_dig_port(intel_dp)->base;
-	bool sink_can_mst = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd);
+	bool sink_can_mst = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd) == DRM_DP_MST;
 
 	drm_dbg_kms(&i915->drm,
 		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s\n",

drivers/gpu/drm/nouveau/nouveau_dp.c

@@ -181,7 +181,7 @@ nouveau_dp_probe_dpcd(struct nouveau_connector *nv_connector,
 	if (nouveau_mst) {
 		mstm = outp->dp.mstm;
 		if (mstm)
-			mstm->can_mst = drm_dp_read_mst_cap(aux, dpcd);
+			mstm->can_mst = drm_dp_read_mst_cap(aux, dpcd) == DRM_DP_MST;
 	}
 
 	if (nouveau_dp_has_sink_count(connector, outp)) {

include/drm/display/drm_dp_mst_helper.h

@@ -818,7 +818,28 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
 
 void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr);
 
-bool drm_dp_read_mst_cap(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE]);
+/**
+ * enum drm_dp_mst_mode - sink's MST mode capability
+ */
+enum drm_dp_mst_mode {
+	/**
+	 * @DRM_DP_SST: The sink does not support MST nor single stream sideband
+	 * messaging.
+	 */
+	DRM_DP_SST,
+	/**
+	 * @DRM_DP_MST: Sink supports MST, more than one stream and single
+	 * stream sideband messaging.
+	 */
+	DRM_DP_MST,
+	/**
+	 * @DRM_DP_SST_SIDEBAND_MSG: Sink supports only one stream and single
+	 * stream sideband messaging.
+	 */
+	DRM_DP_SST_SIDEBAND_MSG,
+};
+
+enum drm_dp_mst_mode drm_dp_read_mst_cap(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE]);
 int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state);
 
 int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr *mgr,