linux-kernel - [PATCH] drm/amd/display: avoid stringop-overflow warnings for dp_decide_lane

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Message-Id: <20231122221421.2944301-1-arnd@kernel.org>
Date:   Wed, 22 Nov 2023 23:13:36 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Wenjing Liu <wenjing.liu@....com>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        George Shen <george.shen@....com>, Jun Lei <Jun.Lei@....com>,
        Michael Mityushkin <michael.mityushkin@....com>,
        Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
        Alan Liu <haoping.liu@....com>,
        Michael Strauss <michael.strauss@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/amd/display: avoid stringop-overflow warnings for dp_decide_lane_settings()

From: Arnd Bergmann <arnd@...db.de>

gcc prints a warning about a possible array overflow for a couple of
callers of dp_decide_lane_settings() after commit 1b56c90018f0 ("Makefile:
Enable -Wstringop-overflow globally"):

drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c: In function 'dp_perform_fixed_vs_pe_training_sequence_legacy':
drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c:426:25: error: 'dp_decide_lane_settings' accessing 4 bytes in a region of size 1 [-Werror=stringop-overflow=]
  426 |                         dp_decide_lane_settings(lt_settings, dpcd_lane_adjust,
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  427 |                                         lt_settings->hw_lane_settings, lt_settings->dpcd_lane_settings);
      |                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c:426:25: note: referencing argument 4 of type 'union dpcd_training_lane[4]'

I'm not entirely sure what caused this, but changing the prototype to expect
a pointer instead of an array avoids the warnings.

Fixes: 7727e7b60f82 ("drm/amd/display: Improve robustness of FIXED_VS link training at DP1 rates")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 .../gpu/drm/amd/display/dc/link/protocols/link_dp_training.c    | 2 +-
 .../gpu/drm/amd/display/dc/link/protocols/link_dp_training.h    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

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 90339c2dfd84..5a0b04518956 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
@@ -807,7 +807,7 @@ void dp_decide_lane_settings(
 		const struct link_training_settings *lt_settings,
 		const union lane_adjust ln_adjust[LANE_COUNT_DP_MAX],
 		struct dc_lane_settings hw_lane_settings[LANE_COUNT_DP_MAX],
-		union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX])
+		union dpcd_training_lane *dpcd_lane_settings)
 {
 	uint32_t lane;
 
diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
index 7d027bac8255..851bd17317a0 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
@@ -111,7 +111,7 @@ void dp_decide_lane_settings(
 	const struct link_training_settings *lt_settings,
 	const union lane_adjust ln_adjust[LANE_COUNT_DP_MAX],
 	struct dc_lane_settings hw_lane_settings[LANE_COUNT_DP_MAX],
-	union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX]);
+	union dpcd_training_lane *dpcd_lane_settings);
 
 enum dc_dp_training_pattern decide_cr_training_pattern(
 		const struct dc_link_settings *link_settings);
-- 
2.39.2