linux-kernel - Re: how to use TLB to prevent Linux accessing a particular memory region

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Message-ID: <Pine.LNX.4.61.0710161040001.11465@chaos.analogic.com>
Date:	Tue, 16 Oct 2007 10:53:53 -0400
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"veerasena reddy" <veerasena_b@...oo.co.in>
Cc:	"linux-kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mips" <linux-mips@...ux-mips.org>
Subject: Re: how to use TLB to prevent Linux accessing a particular memory region 

On Tue, 16 Oct 2007, veerasena reddy wrote:

> Hi,
>
> I have a board, which has two processors ( one is MIPS
> on which Linux-2.6.18 kernel runs and another is DSP
> based processor) and 32MB DDR.
>
> Out of 32MB of DDR 8MB is reserved for use by DSP
> processor. But the MIPS processor downloads firmware
> into this reserved memory for the DSP.
>
> Now, is it possible to use the TLB to prevent Linux
> from accessing the reserved memory after the firmware
> has been downloaded?
>
> Also we'd need to remove those TLB entries if the
> firmware would ever need to be reloaded to the DSP'
> memory region.
>
> What are the APIs to be used to achieve the above?
>
>
> Thanks in advance.
>
> Regards,
> Veerasena.
>
>
>      5, 50, 500, 5000 - Store N number of mails in your inbox. Go to http://help.yahoo.com/l/in/yahoo/mail/yahoomail/tools/tools-08.html
> -

Can't you just memory-map the area you need? That reserves it
until it's unmapped. You don't need to directly touch the TLB.
If you need a physical location, use ioremap_nocache() in your
driver. If you can't get your physical location because the
kernel already uses it, boot the kernel with mem=xxx on the
command-line to prevent the kernel from using memory you
want to reserve for your DSP. You can use num_physpages
(an integer) to find out the last page the kernel uses.

BTW, if this is a new design, most DSP devices put their
RAM on their own board so you don't have these problems.
That RAM gets mmaped to user-space as needed for access,
that address being set asside in PCI space.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.59 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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