linux-kernel - Re: [PATCH 00/03][RFC] Reusable UIO Platform Driver

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Message-ID: <20080521080503.GA28751@digi.com>
Date:	Wed, 21 May 2008 10:05:03 +0200
From:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
To:	Paul Mundt <lethal@...ux-sh.org>,
	Magnus Damm <magnus.damm@...il.com>,
	"Hans J. Koch" <hjk@...utronix.de>, <linux-kernel@...r.kernel.org>,
	<gregkh@...e.de>, <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 00/03][RFC] Reusable UIO Platform Driver

Paul Mundt wrote:
> On Wed, May 21, 2008 at 08:49:38AM +0200, Uwe Kleine-K?nig wrote:
> > Magnus Damm wrote:
> > >         Extending uio_pdrv driver with a chunk of physically
> > > contiguous memory isn't a big deal though.
> > I wonder how you use that memory.  Isn't it just some kind of shared
> > memory?  If so, why not use normal shared memory?  Do you really need
> > that?
> > 
> Physically contiguous memory is a real requirement, especially for DMA.
> I'm not sure what's confusing about that?
I got that, yes.  The problem is I don't see how you can use it for DMA.
The physical address is stored in info->mem[$last].internal_addr and if
there is a way to access that variable from user space, I don't see it
and would appretiate a hint.  Sorry for not expressing my concern more
clear at the first go.  I hope it's understandable now.

@Magnus: Maybe you can provide the userspace part of the driver?
How is that mapping used there?

Best regards
Uwe

-- 
Uwe Kleine-König, Software Engineer
Digi International GmbH Branch Breisach, Küferstrasse 8, 79206 Breisach, Germany
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