linux-kernel - [PATCH AUTOSEL 6.6 03/23] drm/amd/display: add workaround flag to link to force FFE preset

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Message-Id: <20250403191816.2681439-3-sashal@kernel.org>
Date: Thu,  3 Apr 2025 15:17:56 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Brendan Tam <Brendan.Tam@....com>,
	Wenjing Liu <wenjing.liu@....com>,
	Aurabindo Pillai <aurabindo.pillai@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Sasha Levin <sashal@...nel.org>,
	harry.wentland@....com,
	sunpeng.li@....com,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	aric.cyr@....com,
	siqueira@...lia.com,
	alex.hung@....com,
	roman.li@....com,
	dillon.varone@....com,
	Samson.Tam@....com,
	Syed.Hassan@....com,
	george.shen@....com,
	Cruise.Hung@....com,
	joshua.aberback@....com,
	PeiChen.Huang@....com,
	michael.strauss@....com,
	jerry.zuo@....com,
	ivlipski@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.6 03/23] drm/amd/display: add workaround flag to link to force FFE preset

From: Brendan Tam <Brendan.Tam@....com>

[ Upstream commit 51d1b338541dea83fec8e6f95d3e46fa469a73a8 ]

[Why]
There have been instances of some monitors being unable to link train on
their reported link speed using their selected FFE preset. If a different
FFE preset is found that has a higher rate of success during link training
this workaround can be used to force its FFE preset.

[How]
A new link workaround flag is made called force_dp_ffe_preset. The flag is
checked in override_training_settings and will set lt_settings->ffe_preset
which is null if the flag is not set. The flag is then set in
override_lane_settings.

Reviewed-by: Wenjing Liu <wenjing.liu@....com>
Signed-off-by: Brendan Tam <Brendan.Tam@....com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@....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/dc.h                             | 2 ++
 .../gpu/drm/amd/display/dc/link/protocols/link_dp_training.c    | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dc.h b/drivers/gpu/drm/amd/display/dc/dc.h
index cc5e01df15135..88e64b280c90f 100644
--- a/drivers/gpu/drm/amd/display/dc/dc.h
+++ b/drivers/gpu/drm/amd/display/dc/dc.h
@@ -1563,7 +1563,9 @@ struct dc_link {
 		bool dongle_mode_timing_override;
 		bool blank_stream_on_ocs_change;
 		bool read_dpcd204h_on_irq_hpd;
+		bool force_dp_ffe_preset;
 	} wa_flags;
+	union dc_dp_ffe_preset forced_dp_ffe_preset;
 	struct link_mst_stream_allocation_table mst_stream_alloc_table;
 
 	struct dc_link_status link_status;
diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
index 9d1adfc09fb2a..51e88efee11e4 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
@@ -697,6 +697,8 @@ void override_training_settings(
 		lt_settings->pre_emphasis = overrides->pre_emphasis;
 	if (overrides->post_cursor2 != NULL)
 		lt_settings->post_cursor2 = overrides->post_cursor2;
+	if (link->wa_flags.force_dp_ffe_preset && !dp_is_lttpr_present(link))
+		lt_settings->ffe_preset = &link->forced_dp_ffe_preset;
 	if (overrides->ffe_preset != NULL)
 		lt_settings->ffe_preset = overrides->ffe_preset;
 	/* Override HW lane settings with BIOS forced values if present */
-- 
2.39.5