[RFC 4/4] drm/i915/mst: enable MST mode for 128b/132b single-stream sideband

[Jani Nikula]

If the sink supports 128b/132b and single-stream sideband messaging,
enable MST mode.

With this, the topology manager will still write DP_MSTM_CTRL, which
should be ignored by the sink. In the future,
drm_dp_mst_topology_mgr_set_mst() bool mst_state parameter should
probably be turned into an enum drm_dp_mst_mode mst_mode parameter.

Cc: Arun R Murthy <arun.r.murthy at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 4dd9c50226d1..16130e87dc23 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4020,7 +4020,9 @@ static bool intel_dp_mst_detect(struct intel_dp *intel_dp)
 
 	intel_dp->is_mst = i915->display.params.enable_dp_mst &&
 		intel_dp_mst_source_support(intel_dp) &&
-		sink_mst_mode == DP_MST_CAPABLE;
+		(sink_mst_mode == DP_MST_CAPABLE ||
+		 (sink_mst_mode == DP_MST_SIDEBAND_MSG &&
+		  intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B));
 
 	drm_dbg_kms(&i915->drm,
 		    "[ENCODER:%d:%s] MST support: port: %s, sink: %s, modparam: %s -> enable: %s\n",
-- 
2.39.2