From 715c11ee95c2ebf7ea141a74d86f25191083bbba Mon Sep 17 00:00:00 2001
From: Jimmy Kizito <Jimmy.Kizito@amd.com>
Date: Wed, 25 Aug 2021 19:12:08 -0400
Subject: drm/amd/display: Fix link training fallback logic
Git-commit: 4de0bfe67bc98fb2a1115bc58ef3b9bc21717629
Patch-mainline: v5.16-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

[Why]
Link training should fail if stream bandwidth exceeds link bandwidth.

[How]
Correct fallback logic and use named variables to make intention clear.

Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Jimmy Kizito <Jimmy.Kizito@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index b696dca28f63..a594b3d4f6cf 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -2455,12 +2455,16 @@ bool perform_link_training_with_retries(
 			if (type == dc_connection_none)
 				break;
 		} else if (do_fallback) {
+			uint32_t req_bw;
+			uint32_t link_bw;
+
 			decide_fallback_link_setting(*link_setting, &current_setting, status);
 			/* Fail link training if reduced link bandwidth no longer meets
 			 * stream requirements.
 			 */
-			if (dc_bandwidth_in_kbps_from_timing(&stream->timing) <
-					dc_link_bandwidth_kbps(link, &current_setting))
+			req_bw = dc_bandwidth_in_kbps_from_timing(&stream->timing);
+			link_bw = dc_link_bandwidth_kbps(link, &current_setting);
+			if (req_bw > link_bw)
 				break;
 		}
 
-- 
2.38.1