address translation

Gary Thomas gary at
Thu May 15 21:46:20 EST 2003

On Thu, 2003-05-15 at 05:29, Trevor Woerner wrote:
> I want to setup a mapping so that when anything tries to read/write the
> 16 bytes at 0x1f0 - 0x1ff the actual physical memory that gets accessed
> is 0xf7000000 - 0xf700000f.
> I can't figure out what I need to call to get this done.
> ioremap() is the exact opposite of what I want.
> remap_page_range() comes very close but aligns everything to the page
> boundary. In other words, after I do the mapping with either 0x1f0 or
> 0x0 as the virtual address, accessing 0x1f0 gives me 0xf70001f0 instead
> of 0xf7000000. I don't want *page* translation, I need
> *address-for-address* translation (if such a thing is possible). I
> tried setting the physical address to 0xf7000000 - 0x1f0 but that
> didn't work (I didn't think it would :-)
> I think resetting _IO_BASE is just another page translation trick.
> I also tried using io_block_mapping(), which I use in my platform io
> setup routine, but the MMU crashed with one of those '###A' reports.

The memory management on the PowerPC does not have this capability.

I'd suggest rethinking how you are looking at this problem.
  * What is it that wants access to this specific range of physical
    memory in such a way?
Perhaps a specialized device driver would be a better choice.

Gary Thomas <gary at>
MLB Associates

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