drm/amd/display: retry 3 times before successfully reading

DPCD Extended Receiver Capability Field

[Why]
1.dpcd extended receiver capability sometimes read fail,
  and corrupted data leads to sink caps is not correct.
2.sometimes sink reply ack with fewer data

[How]
  check the return value of core_link_read_dpcd,
  try to read again when failure happens
Signed-off-by: Xiaodong Yan <Xiaodong.Yan@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -2371,11 +2371,22 @@ static bool retrieve_link_cap(struct dc_link *link)
 			dpcd_data[DP_TRAINING_AUX_RD_INTERVAL];
 
 		if (aux_rd_interval.bits.EXT_RECIEVER_CAP_FIELD_PRESENT == 1) {
-			core_link_read_dpcd(
+			uint8_t ext_cap_data[16];
+
+			memset(ext_cap_data, '\0', sizeof(ext_cap_data));
+			for (i = 0; i < read_dpcd_retry_cnt; i++) {
+				status = core_link_read_dpcd(
 				link,
 				DP_DP13_DPCD_REV,
-				dpcd_data,
-				sizeof(dpcd_data));
+				ext_cap_data,
+				sizeof(ext_cap_data));
+				if (status == DC_OK) {
+					memcpy(dpcd_data, ext_cap_data, sizeof(dpcd_data));
+					break;
+				}
+			}
+			if (status != DC_OK)
+				dm_error("%s: Read extend caps data failed, use cap from dpcd 0.\n", __func__);
 		}
 	}