Re: generic page.h problem

From: Arnd Bergmann
Date: Wed Mar 23 2011 - 15:53:49 EST

On Wednesday 23 March 2011 20:12:53 Mark Salter wrote:
> I'm working with a new architecture port (nommu) and was wanting to use
> the generic page.h but there is a problem. I'm using CONFIG_FLATMEM with
> a non-zero CONFIG_KERNEL_RAM_BASE_ADDRESS. The hardware uses this same
> address to access RAM from code and for DMA purposes. The generic page.h
> has:
> #else
> #define PAGE_OFFSET (0)
> #endif
> #ifndef __ASSEMBLY__
> #define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET))
> #define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
> The problem I have is that __va(x) and __pa(x) should do nothing on
> this architecture. If I use the following, then everything seems to
> work as it should.
> diff --git a/include/asm-generic/page.h b/include/asm-generic/page.h
> index 75fec18..4dc4a81 100644
> --- a/include/asm-generic/page.h
> +++ b/include/asm-generic/page.h
> @@ -73,8 +73,8 @@ extern unsigned long memory_end;
> #ifndef __ASSEMBLY__
> -#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET))
> -#define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
> +#define __va(x) ((void *)((unsigned long) (x)))
> +#define __pa(x) ((unsigned long) (x))
> #define virt_to_pfn(kaddr) (__pa(kaddr) >> PAGE_SHIFT)
> #define pfn_to_virt(pfn) __va((pfn) << PAGE_SHIFT)
> Am I missing something here? The only other arch using the generic
> page.h is blackfin, but it uses a zero PAGE_OFFSET, so my patch
> would have no effect there.

I don't think the handling of nonzero PAGE_OFFSET in asm-generic/page.h
was intentional. When Remis worked on the patch to introduce this file,
the idea was to take the common parts from all related architectures
and come up with a way that works on most of them.

Maybe one of the other arch maintainers has an opinion on this. If
not, I don't mind your patch, just add that to your series when submitting
the architecture for review.

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