Re: question about __virt_to_phys and __phys_to_virt

["mahaveer darade" <mah.darade@xxxxxxxxx>]

these are used in context of dma mapping. go through documentation/dma-mapping.txt for more information.

On Wed, Dec 3, 2008 at 9:11 AM, loody <miloody@xxxxxxxxx> wrote:

Dear all:
If I remember correctly, the translation between virtual and physical
memory should use page table.
But in include/asm/memory.h, these 2 functions seem don't use page
table to do the translation.

#define __virt_to_phys(x)       ((x) - PAGE_OFFSET + PHYS_OFFSET)
#define __phys_to_virt(x)       ((x) - PHYS_OFFSET + PAGE_OFFSET)

where
in mmu mode
#define PHYS_OFFSET     UL(0x00000000)

#ifndef PAGE_OFFSET
#define PAGE_OFFSET             UL(0xc0000000)
#endif



not in mmu mode
#ifndef PHYS_OFFSET
#define PHYS_OFFSET             (CONFIG_DRAM_BASE)
#endif

#ifndef PAGE_OFFSET
#define PAGE_OFFSET             (PHYS_OFFSET)
#endif

Why they don't need page table to do the page table translation?

cz they are directly mapped.
 

Except the caller is at the first page and in kernel, the first page
is located at the first frame.
thanks for your help,
miloody

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Thanks,
Mahaveer
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