AFT <aftnix@xxxxxxxxx> writes:
> My source is from 2.6 git tree. In LDD3 its said that a logical address
> is mapped to physical address and vice versa by the macros __va() and
> __pa().
>
> In my source tree they are defined as follows:
>
> <include/asm-generic/page.h>
There's an important comment in the beginning of that file:
/*
* Generic page.h implementation, for NOMMU architectures.
* This provides the dummy definitions for the memory management.
*/
> #define __va(x) ((void *)((unsigned long) (x)))
> #define __pa(x) ((unsigned long) (x))
>
>
> I'm not actually understanding how these "cute" looking casting is
> performing "address mapping". I thought address mapping involves more
> complex operations.
The dummy definition is the identity mapping. You can look at the real
implementations to see more complex mappings:
bjorn@nemi:/usr/local/src/git/linux$ egrep '#define __(p|v)a\(' arch/*/include/asm/page.h
arch/alpha/include/asm/page.h:#define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
arch/alpha/include/asm/page.h:#define __va(x) ((void *)((unsigned long) (x) + PAGE_OFFSET))
arch/avr32/include/asm/page.h:#define __pa(x) PHYSADDR(x)
arch/avr32/include/asm/page.h:#define __va(x) ((void *)(P1SEGADDR(x)))
arch/frv/include/asm/page.h:#define __pa(vaddr) virt_to_phys((void *) (unsigned long) (vaddr))
arch/frv/include/asm/page.h:#define __va(paddr) phys_to_virt((unsigned long) (paddr))
arch/h8300/include/asm/page.h:#define __pa(vaddr) virt_to_phys(vaddr)
arch/h8300/include/asm/page.h:#define __va(paddr) phys_to_virt((unsigned long)paddr)
arch/hexagon/include/asm/page.h:#define __pa(x) ((unsigned long)(x) - PAGE_OFFSET)
arch/hexagon/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET))
arch/ia64/include/asm/page.h:#define __pa(x) ({ia64_va _v; _v.l = (long) (x); _v.f.reg = 0; _v.l;})
arch/ia64/include/asm/page.h:#define __va(x) ({ia64_va _v; _v.l = (long) (x); _v.f.reg = -1; _v.p;})
arch/m32r/include/asm/page.h:#define __pa(x) ((unsigned long)(x) - PAGE_OFFSET)
arch/m32r/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET))
arch/mips/include/asm/page.h:#define __pa(x) \
arch/mips/include/asm/page.h:#define __pa(x) \
arch/mips/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET - PHYS_OFFSET))
arch/mn10300/include/asm/page.h:#define __pa(x) ((unsigned long)(x))
arch/mn10300/include/asm/page.h:#define __va(x) ((void *)(unsigned long)(x))
arch/openrisc/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x) + PAGE_OFFSET))
arch/openrisc/include/asm/page.h:#define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
arch/parisc/include/asm/page.h:#define __pa(x) ((unsigned long)(x)-PAGE_OFFSET)
arch/parisc/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
arch/powerpc/include/asm/page.h:#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + VIRT_PHYS_OFFSET))
arch/powerpc/include/asm/page.h:#define __pa(x) ((unsigned long)(x) - VIRT_PHYS_OFFSET)
arch/powerpc/include/asm/page.h:#define __va(x) ((void *)(unsigned long)((phys_addr_t)(x) + PAGE_OFFSET - MEMORY_START))
arch/powerpc/include/asm/page.h:#define __pa(x) ((unsigned long)(x) - PAGE_OFFSET + MEMORY_START)
arch/s390/include/asm/page.h:#define __pa(x) (unsigned long)(x)
arch/s390/include/asm/page.h:#define __va(x) (void *)(unsigned long)(x)
arch/score/include/asm/page.h:#define __pa(x) ((unsigned long)(x) - PAGE_OFFSET)
arch/score/include/asm/page.h:#define __va(x) ((void *)((unsigned long) (x) + PAGE_OFFSET))
arch/sh/include/asm/page.h:#define __pa(x) ___pa((unsigned long)x)
arch/sh/include/asm/page.h:#define __va(x) (void *)___va((unsigned long)x)
arch/tile/include/asm/page.h:#define __pa(kaddr) virt_to_phys((void *)(unsigned long)(kaddr))
arch/tile/include/asm/page.h:#define __va(paddr) phys_to_virt((phys_addr_t)(paddr))
arch/um/include/asm/page.h:#define __pa(virt) to_phys((void *) (unsigned long) (virt))
arch/um/include/asm/page.h:#define __va(phys) to_virt((unsigned long) (phys))
arch/x86/include/asm/page.h:#define __pa(x) __phys_addr((unsigned long)(x))
arch/x86/include/asm/page.h:#define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
arch/xtensa/include/asm/page.h:#define __pa(x) ((unsigned long) (x) - PAGE_OFFSET)
arch/xtensa/include/asm/page.h:#define __va(x) ((void *)((unsigned long) (x) + PAGE_OFFSET))
Bjørn
_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
