drm/amd/display: Adjust DP 8b10b LT exit behavior

[Why]
Polling SINK_STATUS DPCD can cause some non-DP2.0 LTTPR hubs to hang and
no longer respond to AUX.

[How]
As a workaround for the problem hubs, and also to more closely match
DP spec 8b10b behavior, don't poll for intra-hop AUX reply indication
on 8b10b-encoded links.
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1912,7 +1912,7 @@ enum dc_status dpcd_configure_lttpr_mode(struct dc_link *link, struct link_train
 	return status;
 }
 
-static void dpcd_exit_training_mode(struct dc_link *link)
+static void dpcd_exit_training_mode(struct dc_link *link, enum dp_link_encoding encoding)
 {
 	uint8_t sink_status = 0;
 	uint8_t i;
@@ -1920,6 +1920,7 @@ static void dpcd_exit_training_mode(struct dc_link *link)
 	/* clear training pattern set */
 	dpcd_set_training_pattern(link, DP_TRAINING_PATTERN_VIDEOIDLE);
 
+	if (encoding == DP_128b_132b_ENCODING) {
 		/* poll for intra-hop disable */
 		for (i = 0; i < 10; i++) {
 			if ((core_link_read_dpcd(link, DP_SINK_STATUS, &sink_status, 1) == DC_OK) &&
@@ -1927,6 +1928,7 @@ static void dpcd_exit_training_mode(struct dc_link *link)
 				break;
 			udelay(1000);
 		}
+	}
 }
 
 enum dc_status dpcd_configure_channel_coding(struct dc_link *link,
@@ -2649,7 +2651,7 @@ enum link_training_result dc_link_dp_perform_link_training(
 			&lt_settings);
 
 	/* reset previous training states */
-	dpcd_exit_training_mode(link);
+	dpcd_exit_training_mode(link, encoding);
 
 	/* configure link prior to entering training mode */
 	dpcd_configure_lttpr_mode(link, &lt_settings);
@@ -2670,7 +2672,7 @@ enum link_training_result dc_link_dp_perform_link_training(
 		ASSERT(0);
 
 	/* exit training mode */
-	dpcd_exit_training_mode(link);
+	dpcd_exit_training_mode(link, encoding);
 
 	/* switch to video idle */
 	if ((status == LINK_TRAINING_SUCCESS) || !skip_video_pattern)