On 22.12.2010 09:02, Wolfgang Denk wrote:
Dear Alexander Holler,
In message1292711230-3234-1-git-send-email-holler@ahsoftware.de you wrote:
gcc 4.5.1 seems to ignore (at least some) volatile definitions, avoid that as done in the kernel.
...
+#define writeb(v,c) ({ __iowmb(); __arch_putb(v,c); }) +#define writew(v,c) ({ __iowmb(); __arch_putw(v,c); }) +#define writel(v,c) ({ __iowmb(); __arch_putl(v,c); })
http://www.codesourcery.com/archives/arm-gnu/msg03990.html explains why this construct is causing errors in cases where an additional read from the address is unsupported.
Just for the record:
The trick is to ensure that the __arch_putx() containing the volatile is not the last statement in the GCC statement-expression. So, using something like
#define writeb(v,c) ({ __iowmb(); __arch_putb(v,c); v;})
(note the additional 'v;') should result in correct code, too.
The patches sent by Wolfgang and Alexander using
#define writeb(v,c) do { __iowmb(); __arch_putb(v,c); } while (0)
do the same with a slightly different syntax, so these patches are fine, too.
Thanks
Dirk
Can you please try the following patch instead?
From 4672bbddaf8ce7e17a99ba737782cc527d46e5eb Mon Sep 17 00:00:00 2001
From: Alexander Hollerholler@ahsoftware.de Date: Sat, 18 Dec 2010 23:27:10 +0100 Subject: [PATCH] ARM: Avoid compiler optimization for readb, writeb 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.
Signed-off-by: Alexander Hollerholler@ahsoftware.de Signed-off-by: Wolfgang Denkwd@denx.de
arch/arm/include/asm/io.h | 32 ++++++++++++++++++++------------ 1 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h index ff1518e..647503a 100644 --- a/arch/arm/include/asm/io.h +++ b/arch/arm/include/asm/io.h @@ -117,21 +117,29 @@ extern inline void __raw_readsl(unsigned int addr, void *data, int longlen) *buf++ = __arch_getl(addr); }
-#define __raw_writeb(v,a) __arch_putb(v,a) -#define __raw_writew(v,a) __arch_putw(v,a) -#define __raw_writel(v,a) __arch_putl(v,a) +#define __raw_writeb(v,a) __arch_putb(v,a) +#define __raw_writew(v,a) __arch_putw(v,a) +#define __raw_writel(v,a) __arch_putl(v,a)
-#define __raw_readb(a) __arch_getb(a) -#define __raw_readw(a) __arch_getw(a) -#define __raw_readl(a) __arch_getl(a) +#define __raw_readb(a) __arch_getb(a) +#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