[U-Boot] [PATCH v3] ARM: Avoid compiler optimization for usages of readb, writeb and friends.

Alexander Holler
2010-12-22T11:04:22Z

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 <holler@ahsoftware.de>
---
arch/arm/include/asm/io.h | 20 ++++++++++++++------
1 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
index ff1518e..068ed17 100644
--- a/arch/arm/include/asm/io.h
+++ b/arch/arm/include/asm/io.h
@@ -125,13 +125,21 @@ extern inline void __raw_readsl(unsigned int addr, void *data, int longlen)
#define __raw_readw(a) __arch_getw(a)
#define __raw_readl(a) __arch_getl(a)

-#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 __iowmb() dmb()
+
+#define writeb(v,c) do { __iowmb(); __arch_putb(v,c); } while (0)
+#define writew(v,c) do { __iowmb(); __arch_putw(v,c); } while (0)
+#define writel(v,c) do { __iowmb(); __arch_putl(v,c); } while (0)

-#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
--
1.7.2.2