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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     David Gow <davidgow@google.com>,
        Tales Aparecida <tales.aparecida@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Sasha Levin <sashal@kernel.org>, harry.wentland@amd.com,
        sunpeng.li@amd.com, Rodrigo.Siqueira@amd.com,
        christian.koenig@amd.com, Xinhui.Pan@amd.com, airlied@gmail.com,
        daniel@ffwll.ch, isabbasso@riseup.net,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: [PATCH AUTOSEL 4.19 03/10] drm/amd/display: fix overflow on MIN_I64 definition
Date:   Sun,  9 Oct 2022 19:57:38 -0400
Message-Id: <20221009235746.1232129-3-sashal@kernel.org>
In-Reply-To: <20221009235746.1232129-1-sashal@kernel.org>
References: <20221009235746.1232129-1-sashal@kernel.org>
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From: David Gow <davidgow@google.com>

[ Upstream commit 6ae0632d17759852c07e2d1e0a31c728eb6ba246 ]

The definition of MIN_I64 in bw_fixed.c can cause gcc to whinge about
integer overflow, because it is treated as a positive value, which is
then negated. The temporary positive value is not necessarily
representable.

This causes the following warning:
../drivers/gpu/drm/amd/amdgpu/../display/dc/dml/calcs/bw_fixed.c:30:19:
warning: integer overflow in expression ‘-9223372036854775808’ of type
‘long long int’ results in ‘-9223372036854775808’ [-Woverflow]
  30 |         (int64_t)(-(1LL << 63))
     |                   ^

Writing out (-MAX_I64 - 1) works instead.

Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Tales Aparecida <tales.aparecida@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c b/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c
index 6ca288fb5fb9..2d46bc527b21 100644
--- a/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c
+++ b/drivers/gpu/drm/amd/display/dc/calcs/bw_fixed.c
@@ -26,12 +26,12 @@
 #include "bw_fixed.h"
 
 
-#define MIN_I64 \
-	(int64_t)(-(1LL << 63))
-
 #define MAX_I64 \
 	(int64_t)((1ULL << 63) - 1)
 
+#define MIN_I64 \
+	(-MAX_I64 - 1)
+
 #define FRACTIONAL_PART_MASK \
 	((1ULL << BW_FIXED_BITS_PER_FRACTIONAL_PART) - 1)
 
-- 
2.35.1