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Date: Wed, 11 Jul 2007 12:50:20 +0400
From: "Manu Abraham" <abraham.manu@gmail.com>
To: "Nobin Mathew" <nobin.mathew@gmail.com>
Subject: Re: Reading a physical memory location
Cc: "vraghavan3@mail.gatech.edu" <vraghavan3@mail.gatech.edu>,
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On 7/11/07, Nobin Mathew <nobin.mathew@gmail.com> wrote:
> See this in the documentation
>
> The returned virtual address is a current CPU mapping for the memory
> address given. It is only valid to use this function on addresses that
> have a kernel mapping
>
> This function does not handle bus mappings for DMA transfers. In
> almost all conceivable cases a device driver should not be using this
> function
>

To get a better idea, look here
http://tldp.org/LDP/khg/HyperNews/get/devices/addrxlate.html