drm/i915: Set DP min_bpp to 8*3 for non-RGB output formats

6bpc is only legal for RGB and RAW pixel encodings. For the rest
the minimum is 8bpc. Set our lower limit accordingly.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326142556.21176-6-ville.syrjala@linux.intel.comReviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1978,6 +1978,14 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	return 0;
 }
 
+int intel_dp_min_bpp(const struct intel_crtc_state *crtc_state)
+{
+	if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_RGB)
+		return 6 * 3;
+	else
+		return 8 * 3;
+}
+
 static int
 intel_dp_compute_link_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config,
@@ -2001,7 +2009,7 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	limits.min_lane_count = 1;
 	limits.max_lane_count = intel_dp_max_lane_count(intel_dp);
 
-	limits.min_bpp = 6 * 3;
+	limits.min_bpp = intel_dp_min_bpp(pipe_config);
 	limits.max_bpp = intel_dp_compute_bpp(intel_dp, pipe_config);
 
 	if (intel_dp_is_edp(intel_dp)) {

drivers/gpu/drm/i915/intel_dp.h

@@ -34,6 +34,7 @@ void intel_dp_adjust_compliance_config(struct intel_dp *intel_dp,
 				       struct link_config_limits *limits);
 bool intel_dp_limited_color_range(const struct intel_crtc_state *crtc_state,
 				  const struct drm_connector_state *conn_state);
+int intel_dp_min_bpp(const struct intel_crtc_state *crtc_state);
 bool intel_dp_port_enabled(struct drm_i915_private *dev_priv,
 			   i915_reg_t dp_reg, enum port port,
 			   enum pipe *pipe);

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -124,7 +124,7 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	limits.min_lane_count =
 	limits.max_lane_count = intel_dp_max_lane_count(intel_dp);
 
-	limits.min_bpp = 6 * 3;
+	limits.min_bpp = intel_dp_min_bpp(pipe_config);
 	limits.max_bpp = pipe_config->pipe_bpp;
 
 	intel_dp_adjust_compliance_config(intel_dp, pipe_config, &limits);