drm/i915/mst: Limit MST+DSC to TGL+

The MST code currently assumes that glk+ already supports MST+DSC,
which is incorrect. We need to check for TGL+ actually. ICL does
support SST+DSC, but supposedly it can't do MST+FEC which will
also rule out MST+DSC.

Note that a straight TGL+ check doesn't work here because DSC
support can get fused out, so we do need to also check 'has_dsc'.

Cc: stable@vger.kernel.org
Fixes: d51f25eb ("drm/i915: Add DSC support to MST path")
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240402135148.23011-6-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_display_device.h

@@ -47,6 +47,7 @@ struct drm_printer;
 #define HAS_DPT(i915)			(DISPLAY_VER(i915) >= 13)
 #define HAS_DSB(i915)			(DISPLAY_INFO(i915)->has_dsb)
 #define HAS_DSC(__i915)			(DISPLAY_RUNTIME_INFO(__i915)->has_dsc)
+#define HAS_DSC_MST(__i915)		(DISPLAY_VER(__i915) >= 12 && HAS_DSC(__i915))
 #define HAS_FBC(i915)			(DISPLAY_RUNTIME_INFO(i915)->fbc_mask != 0)
 #define HAS_FPGA_DBG_UNCLAIMED(i915)	(DISPLAY_INFO(i915)->has_fpga_dbg)
 #define HAS_FW_BLC(i915)		(DISPLAY_VER(i915) >= 3)

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

@@ -1349,7 +1349,7 @@ intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
 		return 0;
 	}
 
-	if (DISPLAY_VER(dev_priv) >= 10 &&
+	if (HAS_DSC_MST(dev_priv) &&
 	    drm_dp_sink_supports_dsc(intel_connector->dp.dsc_dpcd)) {
 		/*
 		 * TBD pass the connector BPC,