linux-kernel - [PATCH 5.14 069/172] drm/amd/display: Fix Display Flicker on embedded panels

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Date:   Mon,  4 Oct 2021 14:51:59 +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,
        Praful Swarnakar <Praful.Swarnakar@....com>,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 5.14 069/172] drm/amd/display: Fix Display Flicker on embedded panels

From: Praful Swarnakar <Praful.Swarnakar@....com>

commit 083fa05bbaf65a01866b5440031c822e32ad7510 upstream.

[Why]
ASSR is dependent on Signed PSP Verstage to enable Content
Protection for eDP panels. Unsigned PSP verstage is used
during development phase causing ASSR to FAIL.
As a result, link training is performed with
DP_PANEL_MODE_DEFAULT instead of DP_PANEL_MODE_EDP for
eDP panels that causes display flicker on some panels.

[How]
- Do not change panel mode, if ASSR is disabled
- Just report and continue to perform eDP link training
with right settings further.

Signed-off-by: Praful Swarnakar <Praful.Swarnakar@....com>
Reviewed-by: Harry Wentland <harry.wentland@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -1813,14 +1813,13 @@ bool perform_link_training_with_retries(
 		if (panel_mode == DP_PANEL_MODE_EDP) {
 			struct cp_psp *cp_psp = &stream->ctx->cp_psp;
 
-			if (cp_psp && cp_psp->funcs.enable_assr) {
-				if (!cp_psp->funcs.enable_assr(cp_psp->handle, link)) {
-					/* since eDP implies ASSR on, change panel
-					 * mode to disable ASSR
-					 */
-					panel_mode = DP_PANEL_MODE_DEFAULT;
-				}
-			}
+			if (cp_psp && cp_psp->funcs.enable_assr)
+				/* ASSR is bound to fail with unsigned PSP
+				 * verstage used during devlopment phase.
+				 * Report and continue with eDP panel mode to
+				 * perform eDP link training with right settings
+				 */
+				cp_psp->funcs.enable_assr(cp_psp->handle, link);
 		}
 #endif