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

Dirk Behme
2010-12-22T14:50:02Z

On 22.12.2010 12:04, Alexander Holler wrote:
> 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>

This patch seems to be the same as the proposal from Wolfgang

http://lists.denx.de/pipermail/u-boot/2010-December/084122.html

So we shouldn't drop his

Signed-off-by: Wolfgang Denk <wd@denx.de>

Besides of this

Acked-by: Dirk Behme <dirk.behme@googlemail.com>

Thanks

Dirk

> ---
> 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