linux-kernel - Re: Reading a physical memory location

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Message-ID: <46A5F52C.6060101@aitel.hist.no>
Date:	Tue, 24 Jul 2007 14:48:44 +0200
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	vraghavan3@...l.gatech.edu
CC:	Nobin Mathew <nobin.mathew@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Reading a physical memory location

vraghavan3@...l.gatech.edu wrote:
> Thanks for the quick reply. But I was wondering as to why I would have to map
> the physical address to the virtual address when I know that the string is
> permanently in the physical memory because its loaded into flash. 
Because that is how any CPU with a MMU works.
All accesses to memory goes through page tables (virtual memory) -
there is no alternative. But this is not a problem, as the kernel can
map any physical address for you. 

> Is there a way
> to directly read from the physical memory location? 
The way is to map the page containing that address.  You can
then read whatever you want from that page. Nothing is ever accessed
by physical address, physical addresses is only used indirectly
to set up the page tables.

Helge Hafting
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