drm/i915/dp_mst: Disable DSC on ICL MST outputs

Enabling DSC on ICL MST outputs is broken leading to FIFO pipe /
transcoder underruns and blank screen. On TGL+ platforms MST/DSC works -
after fixing the known issues in [1] - however to make this work on ICL
requires more work.

So far DSC on MST probably didn't get enabled for users - due to an issue
fixed by [2] - but after fixing that, DSC could get enabled, leading to a
blank screen in ICL/MST configurations which do work atm. To prevent
this disable MST/DSC on ICL for now.

[1] https://lore.kernel.org/all/20231030155843.2251023-1-imre.deak@intel.com
[2] https://lore.kernel.org/all/20231030155843.2251023-31-imre.deak@intel.com

v2 (Ville):
- Use DISPLAY_VER >= 12 instead of > 11.
- Explain the ICL DSC issue in code comment.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231102194434.2634786-1-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -43,6 +43,7 @@
 #include "intel_dpio_phy.h"
 #include "intel_hdcp.h"
 #include "intel_hotplug.h"
+#include "intel_vdsc.h"
 #include "skl_scaler.h"
 
 static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp,
@@ -297,6 +298,18 @@ static int intel_dp_mst_update_slots(struct intel_encoder *encoder,
 	return 0;
 }
 
+static bool
+intel_dp_mst_dsc_source_support(const struct intel_crtc_state *crtc_state)
+{
+	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
+
+	/*
+	 * FIXME: Enabling DSC on ICL results in blank screen and FIFO pipe /
+	 * transcoder underruns, re-enable DSC after fixing this issue.
+	 */
+	return DISPLAY_VER(i915) >= 12 && intel_dsc_source_support(crtc_state);
+}
+
 static bool
 intel_dp_mst_compute_config_limits(struct intel_dp *intel_dp,
 				   struct intel_crtc_state *crtc_state,
@@ -375,6 +388,9 @@ 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_dsc_source_support(pipe_config))
+			return -EINVAL;
+
 		if (!intel_dp_mst_compute_config_limits(intel_dp,
 							pipe_config,
 							true,