[PATCH v2 3/6] drm/i915/mst: abstract choosing the MST mode to use

[Jani Nikula]

Clarify the conditions for choosing the MST mode to use by adding a new
function intel_dp_mst_mode_choose(). This also prepares for being able
to extend the MST modes to single-stream sideband messaging.

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 | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c 
b/drivers/gpu/drm/i915/display/intel_dp.c
index 944f566525dd..007cb2a04e38 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4015,6 +4015,24 @@ static const char *intel_dp_mst_mode_str(enum 
drm_dp_mst_mode mst_mode)
                return str_yes_no(mst_mode == DRM_DP_MST);
 }
 
+static enum drm_dp_mst_mode
+intel_dp_mst_mode_choose(struct intel_dp *intel_dp,
+                        enum drm_dp_mst_mode sink_mst_mode)
+{
+       struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+
+       if (!i915->display.params.enable_dp_mst)
+               return DRM_DP_SST;
+
+       if (!intel_dp_mst_source_support(intel_dp))
+               return DRM_DP_SST;
+
+       if (sink_mst_mode == DRM_DP_SST_SIDEBAND_MSG)
+               return DRM_DP_SST;
+
+       return sink_mst_mode;
+}
+
 static bool
 intel_dp_mst_detect(struct intel_dp *intel_dp)
 {
@@ -4025,12 +4043,7 @@ intel_dp_mst_detect(struct intel_dp *intel_dp)
 
        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;
+       mst_detect = intel_dp_mst_mode_choose(intel_dp, sink_mst_mode);
 
        drm_dbg_kms(&i915->drm,
                    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: 
%s -> enable: %s\n",
-- 
2.39.2