[U-Boot] [PATCH v4] ARM: Avoid compiler optimization for readb, writeb and friends.

[Thomas Weber <weber@corscience.de>]

Am 09.01.2011 23:19, schrieb Wolfgang Denk:
> From: Alexander Holler <holler@ahsoftware.de>
> 
> 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 Holler <holler@ahsoftware.de>
> Signed-off-by: Dirk Behme <dirk.behme@googlemail.com>
> Signed-off-by: Wolfgang Denk <wd@denx.de>
> Cc: Alessandro Rubini <rubini-list@gnudd.com>
> ---
>  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..3886f15 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)	({ __iowmb(); __arch_putb(v,c); v; })
> +#define writew(v,c)	({ __iowmb(); __arch_putw(v,c); v; })
> +#define writel(v,c)	({ __iowmb(); __arch_putl(v,c); v; })
>  
> -#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

Tested-by: Thomas Weber <weber@corscience.de>

on Devkit8000 with codesourcery arm2010.09 (gcc4.5.1) and arm2010q1 (gcc
4.4.1)