linux-kernel - Re: [linux-dvb] [PATCH] Userspace tuner

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Message-ID: <20070914161345.GB8998@8bytes.org>
Date:	Fri, 14 Sep 2007 18:13:46 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Manu Abraham <abraham.manu@...il.com>
Cc:	Markus Rechberger <mrechberger@...il.com>,
	"linux-dvb@...uxtv.org" <linux-dvb@...uxtv.org>,
	"video4linux-list@...hat.com" <video4linux-list@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [linux-dvb] [PATCH] Userspace tuner

On Fri, Sep 14, 2007 at 04:00:30PM +0400, Manu Abraham wrote:
> Joerg Roedel wrote:
> > On Fri, Sep 14, 2007 at 11:57:59AM +0400, Manu Abraham wrote:
> >>>>> What do you think about IOMMU?
> >>>>>
> >>>>>
> >>>> Just because AMD or INTEL want to invent some whizzy new technology it
> >>>> doesn't say anything about the TV card development and retail business.
> >>>> Intel and AMD have teams of Linux engineers helping operating system
> >>>> developers bring their ideas and technologies to new platforms. That's a
> >>>> million miles away from any of the TV board vendors I know of, who have
> >>>> little or NO fulltime linux developers and consider the < 5% market
> >>>> fringe at best.
> >>>>
> >>> it helps to virtualize devices and introduces newer features for that.
> >>> Some interesting projects could be derrived out of that, there are
> >>> quite a few interesting papers floating around how drivers could be
> >>> handled in future.
> >>>
> >> IOMMU can be considered similar to the AGP GART, which is similar,
> >> remapping the Addresses, as far as i understand.
> > 
> > Common new IOMMUs have only very few in common with the AGP GART. In
> > fact, with current modern IOMMU hardware it will be possible to
> > implement secure userspace device drivers that are even able to do DMA.
> > This is not possible with the GART.
> > 
> >> Though you get a physical to virtual translation, what about interrupts,
> > 
> > Modern IOMMUs are able to remap interrupts. This will solve the problem
> > with PCI interrupt sharing.
> 
> What CPU's are we talking about ?

IOMMUs are not necessarily a CPU feature. These IOMMUS will be found in
the South/North Bridge or even on PCI devices itself (uncommon). The
Calgary IOMMU is such an example of an IOMMU not implemented on the CPU
itself.

Joerg
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