drm/amd/display: Do not retain link settings

Do not retrain link settings if lane count and link rate are both
unknown.  Causes driver to be stuck reading VBIOS register after
removing emulated connection.
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -52,6 +52,8 @@
 #include "dm_helpers.h"
 #include "mem_input.h"
 #include "hubp.h"
+
+#include "dc_link_dp.h"
 #define DC_LOGGER \
 	dc->ctx->logger
 
@@ -419,8 +421,17 @@ void dc_link_set_preferred_link_settings(struct dc *dc,
 					 struct dc_link_settings *link_setting,
 					 struct dc_link *link)
 {
-	link->preferred_link_setting = *link_setting;
-	dp_retrain_link_dp_test(link, link_setting, false);
+	struct dc_link_settings store_settings = *link_setting;
+	struct dc_stream_state *link_stream =
+		link->dc->current_state->res_ctx.pipe_ctx[0].stream;
+
+	link->preferred_link_setting = store_settings;
+	if (link_stream)
+		decide_link_settings(link_stream, &store_settings);
+
+	if ((store_settings.lane_count != LANE_COUNT_UNKNOWN) &&
+		(store_settings.link_rate != LINK_RATE_UNKNOWN))
+		dp_retrain_link_dp_test(link, &store_settings, false);
 }
 
 void dc_link_enable_hpd(const struct dc_link *link)