drm/i915/dp: Validate modes using max Output BPP and slice count when DSC supported

When DSC is supported we need to validate the modes based on the
maximum supported compressed BPP and maximum supported slice count.
This allows us to allow the modes with pixel clock greater than the
available link BW as long as it meets the compressed BPP
and slice count requirements.

v3:
* Use the macro for dsc sink support (Jani N)
v2:
* Properly comment why we are right shifting the bpp value (Anusha)

Cc: Gaurav K Singh <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Ville Syrjala <[e-mail]>
Cc: Anusha Srivatsa <[e-mail]>
Signed-off-by: Manasi Navare <[e-mail]>
Reviewed-by: Anusha Srivatsa <[e-mail]>
Reviewed-by: Gaurav K Singh <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/intel_dp.c

···
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct intel_connector *intel_connector = to_intel_connector(connector);
 	struct drm_display_mode *fixed_mode = intel_connector->panel.fixed_mode;
+	struct drm_i915_private *dev_priv = to_i915(connector->dev);
 	int target_clock = mode->clock;
 	int max_rate, mode_rate, max_lanes, max_link_clock;
 	int max_dotclk;
+	u16 dsc_max_output_bpp = 0;
+	u8 dsc_slice_count = 0;
 
 	if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return MODE_NO_DBLESCAN;
···
 	max_rate = intel_dp_max_data_rate(max_link_clock, max_lanes);
 	mode_rate = intel_dp_link_required(target_clock, 18);
 
-	if (mode_rate > max_rate || target_clock > max_dotclk)
+	/*
+	 * Output bpp is stored in 6.4 format so right shift by 4 to get the
+	 * integer value since we support only integer values of bpp.
+	 */
+	if ((INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv)) &&
+	    drm_dp_sink_supports_dsc(intel_dp->dsc_dpcd)) {
+		if (intel_dp_is_edp(intel_dp)) {
+			dsc_max_output_bpp =
+				drm_edp_dsc_sink_output_bpp(intel_dp->dsc_dpcd) >> 4;
+			dsc_slice_count =
+				drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
+								true);
+		} else {
+			dsc_max_output_bpp =
+				intel_dp_dsc_get_output_bpp(max_link_clock,
+							    max_lanes,
+							    target_clock,
+							    mode->hdisplay) >> 4;
+			dsc_slice_count =
+				intel_dp_dsc_get_slice_count(intel_dp,
+							     target_clock,
+							     mode->hdisplay);
+		}
+	}
+
+	if ((mode_rate > max_rate && !(dsc_max_output_bpp && dsc_slice_count)) ||
+	    target_clock > max_dotclk)
 		return MODE_CLOCK_HIGH;
 
 	if (mode->clock < 10000)