linux-kernel - Re: Reserving a fixed physical address page of RAM.

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Message-ID: <21d7e9970611272134g72044fa8u5c5e47842e994fe3@mail.gmail.com>
Date:	Tue, 28 Nov 2006 16:34:28 +1100
From:	"Dave Airlie" <airlied@...il.com>
To:	"Jon Ringle" <jringle@...tical.com>
Cc:	"Robert Hancock" <hancockr@...w.ca>, linux-kernel@...r.kernel.org
Subject: Re: Reserving a fixed physical address page of RAM.

On 11/28/06, Jon Ringle <jringle@...tical.com> wrote:
> Robert Hancock wrote:
> > Jon Ringle wrote:
> >> Hi,
> >>
> >> I need to reserve a page of memory at a specific area of RAM that will
> >> be used as a "shared memory" with another processor over PCI. How can I
> >> ensure that the this area of RAM gets reseved so that the Linux's memory
> >> management (kmalloc() and friends) don't use it?
> >>
> >> Some things that I've considered are iotable_init() and ioremap().
> >> However, I've seen these used for memory mapped IO devices which are
> >> outside of the RAM memory. Can I use them for reseving RAM too?
> >>
> >> I appreciate any advice in this regard.
> >
> > Sounds to me like dma_alloc_coherent is what you want..
> >
> It looks promising, however, I need to reserve a physical address area
> that is well known (so that the code running on the other processor
> knows where in PCI memory to write to). It appears that
> dma_alloc_coherent returns the address that it allocated. Instead I need
> something where I can tell it what physical address and range I want to use.
>

I've seen other projects just boot a 128M board with mem=120M and just
use the 8MB at 120 to talk to the other processor..

Dave.
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