drm/i915/dp: Check if force_dsc_output_format is possible

Currently for testing an output format with DSC, we just force the
output format, without checking if it can be supported.
This also creates an issue where there is a PCON which might need to
convert from forced output format to the format to sink format.
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230817142459.89764-19-ankit.k.nautiyal@intel.com

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

@@ -935,16 +935,42 @@ dfp_can_convert_from_ycbcr444(struct intel_dp *intel_dp,
 	return false;
 }
 
+static bool
+dfp_can_convert(struct intel_dp *intel_dp,
+		enum intel_output_format output_format,
+		enum intel_output_format sink_format)
+{
+	switch (output_format) {
+	case INTEL_OUTPUT_FORMAT_RGB:
+		return dfp_can_convert_from_rgb(intel_dp, sink_format);
+	case INTEL_OUTPUT_FORMAT_YCBCR444:
+		return dfp_can_convert_from_ycbcr444(intel_dp, sink_format);
+	default:
+		MISSING_CASE(output_format);
+		return false;
+	}
+
+	return false;
+}
+
 static enum intel_output_format
 intel_dp_output_format(struct intel_connector *connector,
 		       enum intel_output_format sink_format)
 {
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	enum intel_output_format force_dsc_output_format =
+		intel_dp->force_dsc_output_format;
 	enum intel_output_format output_format;
+	if (force_dsc_output_format) {
+		if (source_can_output(intel_dp, force_dsc_output_format) &&
+		    (!drm_dp_is_branch(intel_dp->dpcd) ||
+		     sink_format != force_dsc_output_format ||
+		     dfp_can_convert(intel_dp, force_dsc_output_format, sink_format)))
+			return force_dsc_output_format;
 
-	if (intel_dp->force_dsc_output_format)
-		return intel_dp->force_dsc_output_format;
+		drm_dbg_kms(&i915->drm, "Cannot force DSC output format\n");
+	}
 
 	if (sink_format == INTEL_OUTPUT_FORMAT_RGB ||
 	    dfp_can_convert_from_rgb(intel_dp, sink_format))