From: Eric Yang <Eric.Yang2@amd.com>
Date: Wed, 1 Nov 2017 15:43:47 -0400
Subject: drm/amd/display: fix MST link training fail division by 0
Git-commit: 00f713c6dc657397ba37b42d7f6887f526c730c6
Patch-mainline: v4.15-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

When link training fail in MST case, we will divide by 0
when calculating avg_time_slots_per_mtp, so we cannot
proceed.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@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_link.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -2318,9 +2318,11 @@ void core_link_enable_stream(
 
 			/* Abort stream enable *unless* the failure was due to
 			 * DP link training - some DP monitors will recover and
-			 * show the stream anyway.
+			 * show the stream anyway. But MST displays can't proceed
+			 * without link training.
 			 */
-			if (status != DC_FAIL_DP_LINK_TRAINING) {
+			if (status != DC_FAIL_DP_LINK_TRAINING ||
+					pipe_ctx->stream->signal == SIGNAL_TYPE_DISPLAY_PORT_MST) {
 				BREAK_TO_DEBUGGER();
 				return;
 			}