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From: Mike Frysinger <vapier.adi@gmail.com>
To: Mark Salter <msalter@redhat.com>
Cc: arnd@arndb.de, linux-kernel@vger.kernel.org
Subject: Re: generic page.h problem
Date: Wed, 23 Mar 2011 15:19:52 -0400	[thread overview]
Message-ID: <AANLkTiks3dUzD5+Ud73CgguYsOUdyBeSNeGH9C0MueUT@mail.gmail.com> (raw)
In-Reply-To: <1300907573.15255.224.camel@deneb.localdomain>

On Wed, Mar 23, 2011 at 15:12, 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:
>
> #ifdef CONFIG_KERNEL_RAM_BASE_ADDRESS
> #define PAGE_OFFSET             (CONFIG_KERNEL_RAM_BASE_ADDRESS)
> #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.

the only arch that defines CONFIG_KERNEL_RAM_BASE_ADDRESS is mn10300,
and it seems that this generic page.h was designed with it in mind.
fwiw, the va/pa defs for mn10300 also ignore PAGE_OFFSET.
-mike

  reply	other threads:[~2011-03-23 19:21 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-23 19:12 generic page.h problem Mark Salter
2011-03-23 19:19 ` Mike Frysinger [this message]
2011-03-23 19:53 ` Arnd Bergmann

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