linux-kernel - generic page.h problem

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Date:	Wed, 23 Mar 2011 15:12:53 -0400
From:	Mark Salter <msalter@...hat.com>
To:	arnd@...db.de
Cc:	linux-kernel@...r.kernel.org
Subject: generic page.h problem

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.

--Mark

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