Re: what is __pa(x)

["Raghu R. Arur" <rra2002@aria.ncl.cs.columbia.edu>]

On Mon, 8 Sep 2003, Kirk True wrote:

> Hi,
>
> > What is __pa(x) function, it said that it translates logical address to
> > physical address by x-PAGE_OFFSET, PAGE_OFFSET is normally something
> > like 0xc0000000, how can this translate? What is x input?
>
> x is a virtual address. Virtual addresses are the physical addresses
> plus PAGE_OFFSET. So to go *back* to a virtual address from a physical
> address as the __pa macro does, you simply do the reverse operation and
> subtract PAGE_OFFSET.
>

 __pa(x) gives the physical address of the given virtual address - x. this
works only for kernel memory and not for user memory.


 Raghu

> That's my understanding, anyway. I'm a newbie too and it might not be
> that simple.
>
> Kirk
>
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