From 36299a15d2723e8d3a38d05a87d48d43be3dcd7d Mon Sep 17 00:00:00 2001
From: "Tianci.Yin" <tianci.yin@amd.com>
Date: Tue, 8 Mar 2022 13:45:45 +0800
Subject: drm/amd/display: fix dp kvm can't light up
Git-commit: 2e9fda82c98b1e417b90ff5a2f8b8b96cac06fc5
Patch-mainline: v5.18-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]
The DP KVM failed to light up, since the lttpr_mode is not reset to
default value when failed to read LTTPR capabilities, and the
variable max_link_rate retains a initial value zero, this cause variable
link_rate be assigned to an error value zero, consquently pixel_clock
get wrong value zero, and kvm can't light up.

[how]
Reset lttpr_mode to default value when failed to read LTTPR
capabilities, so that the link_rate fallbacks to the minimum rate that
supported by link encoder and sink.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Tianci.Yin <tianci.yin@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 | 1 +
 1 file changed, 1 insertion(+)

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 7d88165e8fa2..c35d55fe41ab 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
@@ -5110,6 +5110,7 @@ bool dp_retrieve_lttpr_cap(struct dc_link *link)
 				sizeof(lttpr_dpcd_data));
 		if (status != DC_OK) {
 			DC_LOG_DP2("%s: Read LTTPR caps data failed.\n", __func__);
+			link->lttpr_mode = LTTPR_MODE_NON_LTTPR;
 			return false;
 		}
 
-- 
2.38.1