[PATCH v2 1/2] io: prevent compiler reordering on the default writeX() implementation

Sinan Kaya
2018-03-30T15:58:20Z

The default implementation of mapping writeX() to __raw_writeX() is wrong.
writeX() has stronger ordering semantics. Compiler is allowed to reorder
__raw_writeX().

In the abscence of a write barrier or when using a strongly ordered
architecture, writeX() 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 | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index b4531e3..e8c2078 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -144,6 +144,7 @@ static inline u64 readq(const volatile void __iomem *addr)
#define writeb writeb
static inline void writeb(u8 value, volatile void __iomem *addr)
{
+ barrier();
__raw_writeb(value, addr);
}
#endif
@@ -152,6 +153,7 @@ static inline void writeb(u8 value, volatile void __iomem *addr)
#define writew writew
static inline void writew(u16 value, volatile void __iomem *addr)
{
+ barrier();
__raw_writew(cpu_to_le16(value), addr);
}
#endif
@@ -160,6 +162,7 @@ static inline void writew(u16 value, volatile void __iomem *addr)
#define writel writel
static inline void writel(u32 value, volatile void __iomem *addr)
{
+ barrier();
__raw_writel(__cpu_to_le32(value), addr);
}
#endif
@@ -169,6 +172,7 @@ static inline void writel(u32 value, volatile void __iomem *addr)
#define writeq writeq
static inline void writeq(u64 value, volatile void __iomem *addr)
{
+ barrier();
__raw_writeq(__cpu_to_le64(value), addr);
}
#endif
--
2.7.4