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

[Jani Nikula]

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.mur...@intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nik...@intel.com>
---
 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