Mapping of Device Physical Address to Kernel Virtual address

[弋天 卜]

在 2012-7-10，17:16，"Prabhu nath" <gprabhunath at gmail.com> 写道：

> Thanks for your reply. Plz see inline
> 
> On Tue, Jul 10, 2012 at 11:17 AM, Philipp Ittershagen <p.ittershagen at googlemail.com> wrote:
> 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?
> 
>       Just wanted to have a constant mapping from PA to VA of devices and wanted to have a separate region for vmalloc. 
> 

what do you mean constant?
After mapping, it is constant.
Before mapping, it is constant for 
Low memory region, but is not 
Constant for vmalloc region. 

Vmalloc region is separate in default.
Your change doesn't make any sense.

The most difficult thing for you is
To make sure what do you want to
Do really. Please give detail demand.


> 
> Greetings,
> 
>   Philipp
> 
> 
> [1]: http://www.kernelport.org/defines.html
> 
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