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Subject[PATCH v2 2/2] io: prevent compiler reordering on the default readX() implementation
Date
The default implementation of mapping readX() to __raw_readX() is wrong.
readX() has stronger ordering semantics. Compiler is allowed to reorder
__raw_readX().

In the abscence of a read barrier or when using a strongly ordered
architecture, readX() should at least have a compiler barrier in
it to prevent commpiler from clobbering the execution order.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
---
include/asm-generic/io.h | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index e8c2078..2554f15 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -110,7 +110,12 @@ static inline void __raw_writeq(u64 value, volatile void __iomem *addr)
#define readb readb
static inline u8 readb(const volatile void __iomem *addr)
{
- return __raw_readb(addr);
+ u8 val;
+
+ val = __raw_readb(addr);
+ barrier();
+
+ return val;
}
#endif

@@ -118,7 +123,12 @@ static inline u8 readb(const volatile void __iomem *addr)
#define readw readw
static inline u16 readw(const volatile void __iomem *addr)
{
- return __le16_to_cpu(__raw_readw(addr));
+ u16 val;
+
+ val = __le16_to_cpu(__raw_readw(addr));
+ barrier();
+
+ return val;
}
#endif

@@ -126,7 +136,12 @@ static inline u16 readw(const volatile void __iomem *addr)
#define readl readl
static inline u32 readl(const volatile void __iomem *addr)
{
- return __le32_to_cpu(__raw_readl(addr));
+ u32 val;
+
+ val = __le32_to_cpu(__raw_readl(addr));
+ barrier();
+
+ return val;
}
#endif

@@ -135,7 +150,12 @@ static inline u32 readl(const volatile void __iomem *addr)
#define readq readq
static inline u64 readq(const volatile void __iomem *addr)
{
- return __le64_to_cpu(__raw_readq(addr));
+ u64 val;
+
+ val = __le64_to_cpu(__raw_readq(addr));
+ barrier();
+
+ return val;
}
#endif
#endif /* CONFIG_64BIT */
--
2.7.4
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