[PATCH 20/22] drm/i915/dp_mst: Allow DSC only for sink ports of the first branch device

[Imre Deak]

Atm the driver supports DSC on MST links only by enabling it globally in
the first branch device UFP's physical DPCD (vs. enabling it per-stream
in the virtual DPCD right upstream the DPRX). This means the branch
device will decompress any compressed stream (which it recognizes via
MSA / SDP compression info), but it does this only for streams going to
an SST output port. Accordingly allow DSC only for streams going to an
SST output port of the first branch device.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 26 +++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index bd44a3007b9c8..f7877127097f1 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -336,6 +336,27 @@ intel_dp_mst_compute_config_limits(struct intel_dp *intel_dp,
 						       limits);
 }
 
+static bool intel_dp_mst_port_supports_dsc(struct intel_dp *intel_dp,
+					   struct intel_crtc_state *crtc_state,
+					   struct drm_connector_state *conn_state)
+{
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	struct intel_connector *connector =
+		to_intel_connector(conn_state->connector);
+	struct intel_crtc *crtc =
+		to_intel_crtc(crtc_state->uapi.crtc);
+
+	if (connector->port->parent != intel_dp->mst_mgr.mst_primary) {
+		drm_dbg_kms(&i915->drm,
+			    "[CRTC:%d:%s] DSC only allowed on sink ports of the first branch device\n",
+			    crtc->base.base.id, crtc->base.name);
+
+		return false;
+	}
+
+	return true;
+}
+
 static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
 				       struct intel_crtc_state *pipe_config,
 				       struct drm_connector_state *conn_state)
@@ -379,6 +400,11 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
 			    str_yes_no(ret),
 			    str_yes_no(intel_dp->force_dsc_en));
 
+		if (!intel_dp_mst_port_supports_dsc(intel_dp,
+						    pipe_config,
+						    conn_state))
+			return -EINVAL;
+
 		if (!intel_dp_mst_compute_config_limits(intel_dp,
 							pipe_config,
 							true,
-- 
2.37.2