drm/i915: Use the correct bpp when validating "4:2:0 only" modes

When validating a "YCbCr 4:2:0 only" mode we must take into
account the fact that we're going to be outputting YCbCr
4:2:0 or 4:4:4 (when a DP->HDMI protocol converter is doing
the 4:2:0 downsampling). For YCbCr 4:4:4 the minimum output
bpc is 8, for YCbCr 4:2:0 it'll be half that. The currently
hardcoded 6bpc is only correct for RGB 4:4:4, which we will
never use with these kinds of modes. Figure out what we're
going to output and use the correct min bpp value to validate
whether the link has sufficient bandwidth.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200917214335.3569-3-ville.syrjala@linux.intel.comReviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>

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

@@ -608,6 +608,37 @@ intel_dp_output_format(struct drm_connector *connector,
 		return INTEL_OUTPUT_FORMAT_YCBCR420;
 }
 
+int intel_dp_min_bpp(enum intel_output_format output_format)
+{
+	if (output_format == INTEL_OUTPUT_FORMAT_RGB)
+		return 6 * 3;
+	else
+		return 8 * 3;
+}
+
+static int intel_dp_output_bpp(enum intel_output_format output_format, int bpp)
+{
+	/*
+	 * bpp value was assumed to RGB format. And YCbCr 4:2:0 output
+	 * format of the number of bytes per pixel will be half the number
+	 * of bytes of RGB pixel.
+	 */
+	if (output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
+		bpp /= 2;
+
+	return bpp;
+}
+
+static int
+intel_dp_mode_min_output_bpp(struct drm_connector *connector,
+			     const struct drm_display_mode *mode)
+{
+	enum intel_output_format output_format =
+		intel_dp_output_format(connector, mode);
+
+	return intel_dp_output_bpp(output_format, intel_dp_min_bpp(output_format));
+}
+
 static bool intel_dp_hdisplay_bad(struct drm_i915_private *dev_priv,
 				  int hdisplay)
 {
@@ -687,7 +718,8 @@ intel_dp_mode_valid(struct drm_connector *connector,
 	max_lanes = intel_dp_max_lane_count(intel_dp);
 
 	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
-	mode_rate = intel_dp_link_required(target_clock, 18);
+	mode_rate = intel_dp_link_required(target_clock,
+					   intel_dp_mode_min_output_bpp(connector, mode));
 
 	if (intel_dp_hdisplay_bad(dev_priv, mode->hdisplay))
 		return MODE_H_ILLEGAL;
@@ -2111,19 +2143,6 @@ intel_dp_adjust_compliance_config(struct intel_dp *intel_dp,
 	}
 }
 
-static int intel_dp_output_bpp(enum intel_output_format output_format, int bpp)
-{
-	/*
-	 * bpp value was assumed to RGB format. And YCbCr 4:2:0 output
-	 * format of the number of bytes per pixel will be half the number
-	 * of bytes of RGB pixel.
-	 */
-	if (output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
-		bpp /= 2;
-
-	return bpp;
-}
-
 /* Optimize link config in order: max bpp, min clock, min lanes */
 static int
 intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
@@ -2346,14 +2365,6 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	return 0;
 }
 
-int intel_dp_min_bpp(enum intel_output_format output_format)
-{
-	if (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,