drm/i915/dp: read sink UHBR rates

See if sink supports DP 2.0 128b/132b channel encoding, and update sink
rates accordingly.

FIXME: Also take LTTPR 128b/132b into account.

v2: Add build-time check for ->sink_rates size (Ville)
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/089d807e887d308c52c84cf58dfb6777de18872d.1629735412.git.jani.nikula@intel.com

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

@@ -141,6 +141,26 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
 		intel_dp->sink_rates[i] = dp_rates[i];
 	}
 
+	/*
+	 * Sink rates for 128b/132b. If set, sink should support all 8b/10b
+	 * rates and 10 Gbps.
+	 */
+	if (intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B) {
+		u8 uhbr_rates = 0;
+
+		BUILD_BUG_ON(ARRAY_SIZE(intel_dp->sink_rates) < ARRAY_SIZE(dp_rates) + 3);
+
+		drm_dp_dpcd_readb(&intel_dp->aux,
+				  DP_128B132B_SUPPORTED_LINK_RATES, &uhbr_rates);
+
+		if (uhbr_rates & DP_UHBR10)
+			intel_dp->sink_rates[i++] = 1000000;
+		if (uhbr_rates & DP_UHBR13_5)
+			intel_dp->sink_rates[i++] = 1350000;
+		if (uhbr_rates & DP_UHBR20)
+			intel_dp->sink_rates[i++] = 2000000;
+	}
+
 	intel_dp->num_sink_rates = i;
 }