FAILED: patch "[PATCH] drm/amd/display: Preserve eDP mode on initial ASSR failure" failed to apply to 6.6-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 5e08102d1d336593160d1434261d50b0c0f6cbe6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026100542-ripening-rematch-74c5@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5e08102d1d336593160d1434261d50b0c0f6cbe6 Mon Sep 17 00:00:00 2001
From: Arthur Heymans <arthur@aheymans.xyz>
Date: Sat, 12 Sep 2026 17:11:37 +0200
Subject: [PATCH] drm/amd/display: Preserve eDP mode on initial ASSR failure

Commit 56d8ce9d8c17 ("drm/amd/display: Apply correct panel mode when
reinitializing hardware") made ASSR failure fall back to the default panel
mode unless eDP mode had previously been applied.

However, dc_link is zero-initialized and DP_PANEL_MODE_DEFAULT is zero.
Before the first call to dp_set_panel_mode(), panel_mode therefore looks
like a previously applied default mode. If ASSR setup fails during the
first link training attempt, the driver incorrectly trains the eDP link
using the default scrambling mode.

On a Google Vilboz Chromebook running self-built coreboot firmware and
PSP verstage, this leaves the panel mostly black with corrupted output
along the top edge.

Track whether panel_mode has actually been initialized, and only consult
the saved mode after it has been applied. This retains the recovery
behavior while preserving eDP mode during initial link training.

Fixes: 56d8ce9d8c17 ("drm/amd/display: Apply correct panel mode when reinitializing hardware")
Assisted-by: Pi:gpt-5.6-sol
Reviewed-by: George Zhang <george.zhang@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit ccb6c2702033f1002b45807fb3cc938760f26f78)
Cc: stable@vger.kernel.org # 6.4.x

diff --git a/drivers/gpu/drm/amd/display/dc/dc.h b/drivers/gpu/drm/amd/display/dc/dc.h
index 705c500ad711..871063f809dc 100644
--- a/drivers/gpu/drm/amd/display/dc/dc.h
+++ b/drivers/gpu/drm/amd/display/dc/dc.h
@@ -1905,6 +1905,7 @@ struct dc_scratch_space {
 	struct ddc_service *ddc;
 
 	enum dp_panel_mode panel_mode;
+	bool panel_mode_initialized;
 	bool aux_mode;
 
 	/* Private to DC core */
diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c
index 16951a9550f2..21dd91fc8010 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c
@@ -93,6 +93,7 @@ void dp_set_panel_mode(struct dc_link *link, enum dp_panel_mode panel_mode)
 	}
 
 	link->panel_mode = panel_mode;
+	link->panel_mode_initialized = true;
 	DC_LOG_DETECTION_DP_CAPS("%d eDP panel mode supported: %d, enabled: %d\n",
 				 link->link_index,
 				 link->dpcd_caps.panel_mode_edp,
@@ -1297,7 +1298,8 @@ void edp_set_panel_assr(struct dc_link *link, struct pipe_ctx *pipe_ctx,
 
 		result = cp_psp->funcs.enable_assr(cp_psp->handle, link);
 
-		if (!result && link->panel_mode != DP_PANEL_MODE_EDP)
+		if (!result && link->panel_mode_initialized &&
+		    link->panel_mode != DP_PANEL_MODE_EDP)
 			*panel_mode = DP_PANEL_MODE_DEFAULT;
 	}
 }