linux-kernel - [PATCH 5.16 057/285] drm/amd/display: reset lane settings after each PHY repeater LT

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Message-Id: <20220412062945.316287675@linuxfoundation.org>
Date:   Tue, 12 Apr 2022 08:28:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Meenakshikumar Somasundaram <Meenakshikumar.Somasundaram@....com>,
        Jun Lei <Jun.Lei@....com>, Jasdeep Dhillon <jdhillon@....com>,
        Sung Joon Kim <sungkim@....com>,
        Daniel Wheeler <daniel.wheeler@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 057/285] drm/amd/display: reset lane settings after each PHY repeater LT

From: Sung Joon Kim <sungkim@....com>

[ Upstream commit 3b853c316c9321e195414a6fb121d1c2d45b1e87 ]

[why]
In LTTPR non-transparent mode, we need
to reset the cached lane settings before performing
link training on the next PHY repeater. Otherwise,
the cached lane settings will be used for the next
clock recovery e.g. VS = MAX (3) which should not be
the case according to the DP specs. We expect to use
minimum lane settings on each clock recovery sequence.

[how]
Reset DPCD and HW lane settings on each repeater LT.
Set training pattern to 0 for the repeater that failed LT
at the proper place.

Reviewed-by: Meenakshikumar Somasundaram <Meenakshikumar.Somasundaram@....com>
Reviewed-by: Jun Lei <Jun.Lei@....com>
Acked-by: Jasdeep Dhillon <jdhillon@....com>
Signed-off-by: Sung Joon Kim <sungkim@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 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 135ea1c422f2..f46aa7f8c35d 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
@@ -2124,21 +2124,26 @@ static enum link_training_result dp_perform_8b_10b_link_training(
 				repeater_id--) {
 			status = perform_clock_recovery_sequence(link, lt_settings, repeater_id);
 
-			if (status != LINK_TRAINING_SUCCESS)
+			if (status != LINK_TRAINING_SUCCESS) {
+				repeater_training_done(link, repeater_id);
 				break;
+			}
 
 			status = perform_channel_equalization_sequence(link,
 					lt_settings,
 					repeater_id);
 
+			repeater_training_done(link, repeater_id);
+
 			if (status != LINK_TRAINING_SUCCESS)
 				break;
 
-			repeater_training_done(link, repeater_id);
+			for (lane = 0; lane < LANE_COUNT_DP_MAX; lane++) {
+				lt_settings->dpcd_lane_settings[lane].raw = 0;
+				lt_settings->hw_lane_settings[lane].VOLTAGE_SWING = 0;
+				lt_settings->hw_lane_settings[lane].PRE_EMPHASIS = 0;
+			}
 		}
-
-		for (lane = 0; lane < (uint8_t)lt_settings->link_settings.lane_count; lane++)
-			lt_settings->dpcd_lane_settings[lane].raw = 0;
 	}
 
 	if (status == LINK_TRAINING_SUCCESS) {
-- 
2.35.1