[PATCH AUTOSEL 5.19 06/36] drm/amd/display: fix overflow on MIN_I64 definition

Sasha Levin
2022-10-10T00:17:32Z

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/dml/calcs/bw_fixed.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dml/calcs/bw_fixed.c b/drivers/gpu/drm/amd/display/dc/dml/calcs/bw_fixed.c
index 6ca288fb5fb9..2d46bc527b21 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/calcs/bw_fixed.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/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