Subject: [PATCH v4] ARM: Avoid compiler optimization for usages of readb and friends. gcc 4.5.1 seems to ignore (at least some) volatile definitions, avoid that as done in the kernel. Reading C99 6.7.3 8 and the comment 114) there, I think it is a bug of that gcc version to ignore the volatile type qualifier used e.g. in __arch_getl(). Anyway, using a definition as in the kernel headers avoids such optimizations when gcc 4.5.1 is used. Maybe the headers as used in the current linux-kernel should be used, but to avoid large changes, I've just added a small change to the current headers. I haven't add the definitions which are using a memory barrier because I haven't found a place in the kernel where they were actually enabled (CONFIG_ARM_DMA_MEM_BUFFERABLE). Signed-off-by: Alexander Holler Signed-off-by: Wolfgang Denk Signed-off-by: Dirk Behme --- Changes since v3: Drop all changes to writex(). It seems that the compiler issue is only with readx(), so we don't have to touch the writex() macros. With not touching the writex() macros, we don't have to care about issues introduced by touching them, too. Note: Tested by compilation only, not tested on real HW. arch/arm/include/asm/io.h | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) Index: u-boot.git/arch/arm/include/asm/io.h =================================================================== --- u-boot.git.orig/arch/arm/include/asm/io.h +++ u-boot.git/arch/arm/include/asm/io.h @@ -128,10 +128,16 @@ extern inline void __raw_readsl(unsigned #define writeb(v,a) __arch_putb(v,a) #define writew(v,a) __arch_putw(v,a) #define writel(v,a) __arch_putl(v,a) +/* + * TODO: The kernel offers some more advanced versions of barriers, it might + * have some advantages to use them instead of the simple one here. + */ +#define dmb() __asm__ __volatile__ ("" : : : "memory") +#define __iormb() dmb() -#define readb(a) __arch_getb(a) -#define readw(a) __arch_getw(a) -#define readl(a) __arch_getl(a) +#define readb(c) ({ u8 __v = __arch_getb(c); __iormb(); __v; }) +#define readw(c) ({ u16 __v = __arch_getw(c); __iormb(); __v; }) +#define readl(c) ({ u32 __v = __arch_getl(c); __iormb(); __v; }) /* * The compiler seems to be incapable of optimising constants