linux-kernel - [PATCH] powerpc/32: Remove memory clobber asm constraint on dcbX() functions

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Date:   Tue,  9 Jan 2018 07:57:59 +0100 (CET)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/32: Remove memory clobber asm constraint on dcbX()
 functions

Instead of just telling GCC that dcbz(), dcbi(), dcbf() and dcbst()
clobber memory, tell it what it clobbers:
* dcbz(), dcbi() and dcbf() clobbers one cacheline as output
* dcbf() and dcbst() clobbers one cacheline as input

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/include/asm/cache.h | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
index c1d257aa4c2d..fc8fe18acf8c 100644
--- a/arch/powerpc/include/asm/cache.h
+++ b/arch/powerpc/include/asm/cache.h
@@ -82,22 +82,31 @@ extern void _set_L3CR(unsigned long);
 
 static inline void dcbz(void *addr)
 {
-	__asm__ __volatile__ ("dcbz 0, %0" : : "r"(addr) : "memory");
+	__asm__ __volatile__ ("dcbz 0, %1" :
+			      "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
+			      "r"(addr) :);
 }
 
 static inline void dcbi(void *addr)
 {
-	__asm__ __volatile__ ("dcbi 0, %0" : : "r"(addr) : "memory");
+	__asm__ __volatile__ ("dcbi 0, %1" :
+			      "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
+			      "r"(addr) :);
 }
 
 static inline void dcbf(void *addr)
 {
-	__asm__ __volatile__ ("dcbf 0, %0" : : "r"(addr) : "memory");
+	__asm__ __volatile__ ("dcbf 0, %1" :
+			      "=m"(*(char (*)[L1_CACHE_BYTES])addr) :
+			      "r"(addr), "m"(*(char (*)[L1_CACHE_BYTES])addr) :
+			     );
 }
 
 static inline void dcbst(void *addr)
 {
-	__asm__ __volatile__ ("dcbst 0, %0" : : "r"(addr) : "memory");
+	__asm__ __volatile__ ("dcbst 0, %0" : :
+			      "r"(addr), "m"(*(char (*)[L1_CACHE_BYTES])addr) :
+			     );
 }
 #endif /* !__ASSEMBLY__ */
 #endif /* __KERNEL__ */
-- 
2.13.3