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MIPS: cmpxchg: Omit redundant barriers for Loongson3 

When building a kernel configured to support Loongson3 LL/SC workarounds
(ie. CONFIG_CPU_LOONGSON3_WORKAROUNDS=y) the inline assembly in
__xchg_asm() & __cmpxchg_asm() already emits completion barriers, and as
such we don't need to emit extra barriers from the xchg() or cmpxchg()
macros. Add compile-time constant checks causing us to omit the
redundant memory barriers.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org
This commit is contained in:
Paul Burton 2019-10-01 21:53:38 +00:00
parent 6a57d2d1e7
commit a91f2a1dba
No known key found for this signature in database
GPG Key ID: 3EA79FACB57500DD
1 changed files with 23 additions and 3 deletions
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26
arch/mips/include/asm/cmpxchg.h
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@ -94,7 +94,13 @@ static inline unsigned long __xchg(volatile void *ptr, unsigned long x,
({ \
__typeof__(*(ptr)) __res; \
\
smp_mb__before_llsc(); \
/* \
* In the Loongson3 workaround case __xchg_asm() already \
* contains a completion barrier prior to the LL, so we don't \
* need to emit an extra one here. \
*/ \
if (!__SYNC_loongson3_war) \
smp_mb__before_llsc(); \
\
__res = (__typeof__(*(ptr))) \
__xchg((ptr), (unsigned long)(x), sizeof(*(ptr))); \
@ -179,9 +185,23 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
({ \
__typeof__(*(ptr)) __res; \
\
smp_mb__before_llsc(); \
/* \
* In the Loongson3 workaround case __cmpxchg_asm() already \
* contains a completion barrier prior to the LL, so we don't \
* need to emit an extra one here. \
*/ \
if (!__SYNC_loongson3_war) \
smp_mb__before_llsc(); \
\
__res = cmpxchg_local((ptr), (old), (new)); \
smp_llsc_mb(); \
\
/* \
* In the Loongson3 workaround case __cmpxchg_asm() already \
* contains a completion barrier after the SC, so we don't \
* need to emit an extra one here. \
*/ \
if (!__SYNC_loongson3_war) \
smp_llsc_mb(); \
\
__res; \
})