From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [RFC PATCH v3 5/7] dma-mapping: detect and configure IOMMU in of_dma_configure Date: Mon, 27 Oct 2014 10:51:59 +0000 Message-ID: <20141027105158.GE8768@arm.com> References: <1410539695-29128-1-git-send-email-will.deacon@arm.com> <20140922092909.GJ1470@ulmo> <20140922175027.GK7936@arm.com> <4572757.M4IDlCz5Vc@avalon> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <4572757.M4IDlCz5Vc@avalon> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Laurent Pinchart Cc: "jroedel-l3A5Bk7waGM@public.gmane.org" , "arnd-r2nGTMty4D4@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , Thierry Reding , "Varun.Sethi-KZfg59tc24xl57MIdRCFDg@public.gmane.org" , "dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: iommu@lists.linux-foundation.org On Tue, Oct 14, 2014 at 01:53:59PM +0100, Laurent Pinchart wrote: > Hi Will, Hi Laurent, > On Monday 22 September 2014 18:50:27 Will Deacon wrote: > > On Mon, Sep 22, 2014 at 10:29:10AM +0100, Thierry Reding wrote: > > > Agreed. I wonder how useful it is to know the set of IOMMU instances > > > that each device can master through. Wouldn't it be more useful to keep > > > a list of master interfaces for each device? The set of IOMMU instances > > > can trivially be derived from that. > > > > I'm struggling to think how that would look. What do you mean by `master > > interfaces' in terms of the code we have in Linux? At the end of the day, > > the list of IOMMU instances (i.e. iommu_dma_mapping) exists because you > > and Laurent have use-cases involving devices mastering through multiple > > IOMMUs. If it doesn't work for you, it might be best for you to send me > > the patch ;) > > Just for the record, I've brought up the topic of masters being served by > multiple IOMMUs, but don't have a use case for it (yet at least). I do have > masters served through multiple streams with separate stream IDs, but all by > the same IOMMU. Ok. I spoke to Arnd, David and Joerg at LPC and the consensus was that the DMA-mapping API should *not* be exposed to the details of masters that master through multiple IOMMUs. Instead, that should be abstracted by the device API by exposing that device as a single struct device. So, that's certainly an area that needs more work and I'll drop the limited support I'd cooked up from this patch set in the next version. Will From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Mon, 27 Oct 2014 10:51:59 +0000 Subject: [RFC PATCH v3 5/7] dma-mapping: detect and configure IOMMU in of_dma_configure In-Reply-To: <4572757.M4IDlCz5Vc@avalon> References: <1410539695-29128-1-git-send-email-will.deacon@arm.com> <20140922092909.GJ1470@ulmo> <20140922175027.GK7936@arm.com> <4572757.M4IDlCz5Vc@avalon> Message-ID: <20141027105158.GE8768@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Oct 14, 2014 at 01:53:59PM +0100, Laurent Pinchart wrote: > Hi Will, Hi Laurent, > On Monday 22 September 2014 18:50:27 Will Deacon wrote: > > On Mon, Sep 22, 2014 at 10:29:10AM +0100, Thierry Reding wrote: > > > Agreed. I wonder how useful it is to know the set of IOMMU instances > > > that each device can master through. Wouldn't it be more useful to keep > > > a list of master interfaces for each device? The set of IOMMU instances > > > can trivially be derived from that. > > > > I'm struggling to think how that would look. What do you mean by `master > > interfaces' in terms of the code we have in Linux? At the end of the day, > > the list of IOMMU instances (i.e. iommu_dma_mapping) exists because you > > and Laurent have use-cases involving devices mastering through multiple > > IOMMUs. If it doesn't work for you, it might be best for you to send me > > the patch ;) > > Just for the record, I've brought up the topic of masters being served by > multiple IOMMUs, but don't have a use case for it (yet at least). I do have > masters served through multiple streams with separate stream IDs, but all by > the same IOMMU. Ok. I spoke to Arnd, David and Joerg at LPC and the consensus was that the DMA-mapping API should *not* be exposed to the details of masters that master through multiple IOMMUs. Instead, that should be abstracted by the device API by exposing that device as a single struct device. So, that's certainly an area that needs more work and I'll drop the limited support I'd cooked up from this patch set in the next version. Will