Hi, On Fri, Mar 30, 2018 at 11:58:13AM -0400, Sinan Kaya wrote: > The default implementation of mapping readX() to __raw_readX() is wrong. > readX() has stronger ordering semantics. Compiler is allowed to reorder > __raw_readX().
Could you please specify what the compiler is potentially reordering __raw_readX() against, and why this would be wrong? e.g. do we care about prior normal memory accesses, subsequent normal memory accesses, and/or other IO accesses? I assume that the asm-generic __raw_{read,write}X() implementations are all ordered w.r.t. each other (at least for a specific device). Thanks, Mark. > 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 <ok...@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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html