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From: Nathan Chancellor <natechancellor@gmail.com>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
	clang-built-linux@googlegroups.com,
	Nathan Chancellor <natechancellor@gmail.com>,
	kernel test robot <lkp@intel.com>
Subject: [PATCH] MIPS: Compare __SYNC_loongson3_war against 0
Date: Thu, 14 Jan 2021 10:34:16 -0700	[thread overview]
Message-ID: <20210114173416.738455-1-natechancellor@gmail.com> (raw)

When building with clang when CONFIG_CPU_LOONGSON3_WORKAROUNDS is
enabled:

 In file included from lib/errseq.c:4:
 In file included from ./include/linux/atomic.h:7:
 ./arch/mips/include/asm/atomic.h:52:1: warning: converting the result of
 '<<' to a boolean always evaluates to true
 [-Wtautological-constant-compare]
 ATOMIC_OPS(atomic64, s64)
 ^
 ./arch/mips/include/asm/atomic.h:40:9: note: expanded from macro
 'ATOMIC_OPS'
         return cmpxchg(&v->counter, o, n);
                ^
 ./arch/mips/include/asm/cmpxchg.h:194:7: note: expanded from macro
 'cmpxchg'
         if (!__SYNC_loongson3_war)
              ^
 ./arch/mips/include/asm/sync.h:147:34: note: expanded from macro
 '__SYNC_loongson3_war'
 # define __SYNC_loongson3_war   (1 << 31)
                                    ^

While it is not wrong that the result of this shift is always true in a
boolean context, it is not a problem here. Regardless, the warning is
really noisy so rather than making the shift a boolean implicitly, use
it in an equality comparison so the shift is used as an integer value.

Fixes: 4d1dbfe6cbec ("MIPS: atomic: Emit Loongson3 sync workarounds within asm")
Fixes: a91f2a1dba44 ("MIPS: cmpxchg: Omit redundant barriers for Loongson3")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/mips/include/asm/atomic.h  | 2 +-
 arch/mips/include/asm/cmpxchg.h | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/mips/include/asm/atomic.h b/arch/mips/include/asm/atomic.h
index f904084fcb1f..27ad76791539 100644
--- a/arch/mips/include/asm/atomic.h
+++ b/arch/mips/include/asm/atomic.h
@@ -248,7 +248,7 @@ static __inline__ int pfx##_sub_if_positive(type i, pfx##_t * v)	\
 	 * bltz that can branch	to code outside of the LL/SC loop. As	\
 	 * such, we don't need to emit another barrier here.		\
 	 */								\
-	if (!__SYNC_loongson3_war)					\
+	if (__SYNC_loongson3_war == 0)					\
 		smp_mb__after_atomic();					\
 									\
 	return result;							\
diff --git a/arch/mips/include/asm/cmpxchg.h b/arch/mips/include/asm/cmpxchg.h
index 5b0b3a6777ea..ed8f3f3c4304 100644
--- a/arch/mips/include/asm/cmpxchg.h
+++ b/arch/mips/include/asm/cmpxchg.h
@@ -99,7 +99,7 @@ unsigned long __xchg(volatile void *ptr, unsigned long x, int size)
 	 * contains a completion barrier prior to the LL, so we don't	\
 	 * need to emit an extra one here.				\
 	 */								\
-	if (!__SYNC_loongson3_war)					\
+	if (__SYNC_loongson3_war == 0)					\
 		smp_mb__before_llsc();					\
 									\
 	__res = (__typeof__(*(ptr)))					\
@@ -191,7 +191,7 @@ unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	 * contains a completion barrier prior to the LL, so we don't	\
 	 * need to emit an extra one here.				\
 	 */								\
-	if (!__SYNC_loongson3_war)					\
+	if (__SYNC_loongson3_war == 0)					\
 		smp_mb__before_llsc();					\
 									\
 	__res = cmpxchg_local((ptr), (old), (new));			\
@@ -201,7 +201,7 @@ unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 	 * contains a completion barrier after the SC, so we don't	\
 	 * need to emit an extra one here.				\
 	 */								\
-	if (!__SYNC_loongson3_war)					\
+	if (__SYNC_loongson3_war == 0)					\
 		smp_llsc_mb();						\
 									\
 	__res;								\

base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
-- 
2.30.0


             reply	other threads:[~2021-01-14 17:35 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14 17:34 Nathan Chancellor [this message]
2021-01-14 17:48 ` Nick Desaulniers
2021-01-15 14:39 ` Thomas Bogendoerfer

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