From: Samson Tam <Samson.Tam@amd.com>
Date: Mon, 30 Jul 2018 12:22:35 -0400
Subject: drm/amd/display: Do not retain link settings
Git-commit: 8f7040b8f252fae4ca5d2453e9f50b78cf6b834f
Patch-mainline: v4.19-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

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>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/amd/display/dc/core/dc.c
+++ b/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_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)