Mapping of Device Physical Address to Kernel Virtual address

[Prabhu nath]

On Tue, Jul 10, 2012 at 10:03 PM, 弋天 卜 <buyit at live.cn> wrote:

>
>
> 在 2012-7-10，17:16，"Prabhu nath" < <gprabhunath at gmail.com>
> 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><p.ittershagen at googlemail.com>
> p.ittershagen at googlemail.com> wrote:
>
>> Hi Prabhu,
>>
>> On Tue, Jul 10, 2012 at 6:56 AM, Prabhu nath < <gprabhunath at gmail.com><gprabhunath at gmail.com>
>> 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.
>

   I mean fixed/static mapping rather than kernel allocating kernel virtual
address dynamically.

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

    You mean ioremap(...) will not map the physical address of the device
into vmalloc region ?

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

    My requirement is very simple. I have designed a layout showing mapping
of physical address to kernel virtual address. I also want to implement in
the same way.

    1. Low mem region - which is already fixed by the kernel based on the
memory size.
    2. Vmalloc region which can be fixed as per your previous mail
    3. Also have a fixed mapping of device physical address by
ioremap_page_range(...)

     I think I got what I needed. Thank you all very much for your valuable
time.

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