[U-Boot] [RFC PATCH v2] ARM: Avoid compiler optimization for usages of readb, writeb and friends.

John Rigby
2010-12-20T16:12:07Z

On Mon, Dec 20, 2010 at 9:08 AM, John Rigby <john.rigby@linaro.org> wrote:
> Earlier in this thread Alexander said:
>> 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).
>
> I think this is the problem because it is indeed defined for all v6
> and v7 arm platforms. ?Here is the config snippet from
> arch/arm/mm/Kconfig:
>
> config ARM_DMA_MEM_BUFFERABLE
> ? ? ? ?bool "Use non-cacheable memory for DMA" if CPU_V6 && !CPU_V7
> ? ? ? ?depends on !(MACH_REALVIEW_PB1176 || REALVIEW_EB_ARM11MP || \
> ? ? ? ? ? ? ? ? ? ? MACH_REALVIEW_PB11MP)
> ? ? ? ?default y if CPU_V6 || CPU_V7
> ? ? ? ?help
> ? ? ? ? ?Historically, the kernel has used strongly ordered mappings to
> ? ? ? ? ?provide DMA coherent memory. ?With the advent of ARMv7, mapping
> ? ? ? ? ?memory with differing types results in unpredictable behaviour,
> ? ? ? ? ?so on these CPUs, this option is forced on.

On second thought maybe this is noise for us in u-boot without
cacheable mappings? Sorry for the noise.

br,

John