Mapping of Device Physical Address to Kernel Virtual address

[Philipp Ittershagen]

Hi Prabhu,

On Tue, Jul 10, 2012 at 6:56 AM, Prabhu nath <gprabhunath at gmail.com> wrote:
> For E.g. I have a device whose physical address range is 0x80008000 to
> 0x80008FFF.
>              Is it possible to map this device physical address to a known
> virtual address range 0xF0008000 to 0xF0008FFF.

I don't think this is possible, because these virtual address ranges
are handled by the kernel VMA system and are allocated dynamically, so
that is not just a bitmask or something to change.

> My hardware configuration has 128 MB of system RAM which will have been
> MAPPED to the Kernel virtual address from 0xC0000000 to 0xC7FFFFFF
>
> Also is it possible to configure the vmalloc kernel virtual address region
> to a fixed range of 128 MB from 0xC8000000 to 0xCFFFFFFF

You could change PAGE_OFFSET. From [1]:


PHYS_OFFSET
	Physical start address of the first bank of RAM.

PAGE_OFFSET
	Virtual start address of the first bank of RAM.  During the kernel
	boot phase, virtual address PAGE_OFFSET will be mapped to physical
	address PHYS_OFFSET, along with any other mappings you supply.
	This should be the same value as TASK_SIZE.


But I'm curious: Why do you want to change it?


Greetings,

  Philipp


[1]: http://www.kernelport.org/defines.html