linux-kernel - Re: reserve memory in low physical address

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Message-ID: <20061031154019.GC14272@srv.junsun.net>
Date:	Tue, 31 Oct 2006 07:40:19 -0800
From:	Jun Sun <jsun@...sun.net>
To:	"Richard B. Johnson" <jmodem@...minablefirebug.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: reserve memory in low physical address - possible?

On Tue, Oct 31, 2006 at 07:32:37AM -0500, Richard B. Johnson wrote:
> 
> You will not be able to reserve any address space starting at 0 anyway, but 
> your driver or even
> user-space code can memory-map it.
> 

Any reasons or concerns as to why I can't reserve any address space 
starting from 0?

To make my motivation clearer, here is the application scenario.

My system will load an initial OS (could be a strip down Linux or some
simple RTOS) into the low memory starting from address 0.  The initial OS
will then load Linux into higher memory region, say @100M.  Then control jumps
to Linux while the initial OS is still lurking in the RAM for future
use.

> Some early (ISA) boards couldn't access address-space beyoond 16 megabytes, 
> hense the "low" memory
> for DMA.
> 

So if I don't have ISA performing DMA, I should be OK in this regard?

Thanks.

Jun
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