drm/amd/display: allow DP40 cables to do UHBR13.5

why:
With DP2.1a expansion we are allowing DP40 cables to do UHBR13.5

how:
Assume UHBR10 means UHBR13.5 also for unknown cable type and
passive cable type.
Reviewed-by: George Shen <george.shen@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Ran Shi <ran.shi@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c

@@ -412,12 +412,18 @@ static enum dc_link_rate get_cable_max_link_rate(struct dc_link *link)
 {
 	enum dc_link_rate cable_max_link_rate = LINK_RATE_UNKNOWN;
 
-	if (link->dpcd_caps.cable_id.bits.UHBR10_20_CAPABILITY & DP_UHBR20)
+	if (link->dpcd_caps.cable_id.bits.UHBR10_20_CAPABILITY & DP_UHBR20) {
 		cable_max_link_rate = LINK_RATE_UHBR20;
-	else if (link->dpcd_caps.cable_id.bits.UHBR13_5_CAPABILITY)
+	} else if (link->dpcd_caps.cable_id.bits.UHBR13_5_CAPABILITY) {
 		cable_max_link_rate = LINK_RATE_UHBR13_5;
-	else if (link->dpcd_caps.cable_id.bits.UHBR10_20_CAPABILITY & DP_UHBR10)
-		cable_max_link_rate = LINK_RATE_UHBR10;
+	} else if (link->dpcd_caps.cable_id.bits.UHBR10_20_CAPABILITY & DP_UHBR10) {
+		// allow DP40 cables to do UHBR13.5 for passive or unknown cable type
+		if (link->dpcd_caps.cable_id.bits.CABLE_TYPE < 2) {
+			cable_max_link_rate = LINK_RATE_UHBR13_5;
+		} else {
+			cable_max_link_rate = LINK_RATE_UHBR10;
+		}
+	}
 
 	return cable_max_link_rate;
 }