[PATCH v2 2/6] drm/i915/mst: improve debug logging of DP MST mode detect

[Jani Nikula <jani.nikula@xxxxxxxxx>]

Rename intel_dp_can_mst() to intel_dp_mst_detect(), and move all DP MST
detect debug logging there. Debug log the sink's MST capability,
including single-stream sideband messaging support, and the decision
whether to enable MST mode or not. Do this regardless of whether we're
actually enabling MST or not.

Cc: Arun R Murthy <arun.r.murthy@xxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 45 +++++++++++++++++--------
 1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index a1c304f451bd..944f566525dd 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4007,31 +4007,48 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 					   intel_dp->downstream_ports) == 0;
 }
 
+static const char *intel_dp_mst_mode_str(enum drm_dp_mst_mode mst_mode)
+{
+	if (mst_mode == DRM_DP_SST_SIDEBAND_MSG)
+		return "single-stream sideband messaging";
+	else
+		return str_yes_no(mst_mode == DRM_DP_MST);
+}
+
 static bool
-intel_dp_can_mst(struct intel_dp *intel_dp)
+intel_dp_mst_detect(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;
+	enum drm_dp_mst_mode sink_mst_mode;
+	enum drm_dp_mst_mode mst_detect;
+
+	sink_mst_mode = drm_dp_read_mst_cap(&intel_dp->aux, intel_dp->dpcd);
+
+	if (i915->display.params.enable_dp_mst &&
+	    intel_dp_mst_source_support(intel_dp) &&
+	    sink_mst_mode == DRM_DP_MST)
+		mst_detect = DRM_DP_MST;
+	else
+		mst_detect = DRM_DP_SST;
 
-	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_MST;
+	drm_dbg_kms(&i915->drm,
+		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s -> enable: %s\n",
+		    encoder->base.base.id, encoder->base.name,
+		    str_yes_no(intel_dp_mst_source_support(intel_dp)),
+		    intel_dp_mst_mode_str(sink_mst_mode),
+		    str_yes_no(i915->display.params.enable_dp_mst),
+		    intel_dp_mst_mode_str(mst_detect));
+
+	return mst_detect != DRM_DP_SST;
 }
 
 static void
 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) == DRM_DP_MST;
 
-	drm_dbg_kms(&i915->drm,
-		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s\n",
-		    encoder->base.base.id, encoder->base.name,
-		    str_yes_no(intel_dp_mst_source_support(intel_dp)),
-		    str_yes_no(sink_can_mst),
-		    str_yes_no(i915->display.params.enable_dp_mst));
-
 	if (!intel_dp_mst_source_support(intel_dp))
 		return;
 
@@ -5390,7 +5407,7 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 		connector_status_connected : connector_status_disconnected;
 	}
 
-	if (intel_dp_can_mst(intel_dp))
+	if (intel_dp_mst_detect(intel_dp))
 		return connector_status_connected;
 
 	/* If no HPD, poke DDC gently */
-- 
2.39.2