linux-kernel - Re: [Linaro-mm-sig] [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

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Message-ID: <7233574.nKiRa7HnXU@wuerfel>
Date:	Tue, 03 Feb 2015 17:36:59 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-kernel@...ts.linaro.org
Cc:	Rob Clark <robdclark@...il.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Tomasz Stanislawski <stanislawski.tomasz@...glemail.com>,
	LKML <linux-kernel@...r.kernel.org>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Daniel Vetter <daniel@...ll.ch>,
	Robin Murphy <robin.murphy@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

On Tuesday 03 February 2015 11:22:01 Rob Clark wrote:
> On Tue, Feb 3, 2015 at 11:12 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > I agree for the case you are describing here. From what I understood
> > from Rob was that he is looking at something more like:
> >
> > Fig 3
> > CPU--L1cache--L2cache--Memory--IOMMU---<iobus>--device
> >
> > where the IOMMU controls one or more contexts per device, and is
> > shared across GPU and non-GPU devices. Here, we need to use the
> > dmap-mapping interface to set up the IO page table for any device
> > that is unable to address all of system RAM, and we can use it
> > for purposes like isolation of the devices. There are also cases
> > where using the IOMMU is not optional.
> 
> 
> Actually, just to clarify, the IOMMU instance is specific to the GPU..
> not shared with other devices.  Otherwise managing multiple contexts
> would go quite badly..
> 
> But other devices have their own instance of the same IOMMU.. so same
> driver could be used.

I think from the driver perspective, I'd view those two cases as
identical. Not sure if Russell agrees with that.

	Arnd
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