From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Wed, 04 Jun 2014 16:01:15 +0200 Message-ID: <13061821.NYx1AfEhs0@wuerfel> References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> <20140604134400.GE28484@ulmo> <20140604135600.GD6644@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140604135600.GD6644-5wv7dgnIgG8@public.gmane.org> 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: Will Deacon Cc: Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Pawel Moll , Ian Campbell , Grant Grundler , Stephen Warren , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Rob Herring , Marc Zyngier , Linux IOMMU , Thierry Reding , Rob Herring , Kumar Gala , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Cho KyongHo , Dave P Martin , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: devicetree@vger.kernel.org On Wednesday 04 June 2014 14:56:01 Will Deacon wrote: > On Wed, Jun 04, 2014 at 02:44:03PM +0100, Thierry Reding wrote: > > On Fri, May 30, 2014 at 09:54:37PM +0200, Arnd Bergmann wrote: > > > On Friday 30 May 2014 22:29:13 Hiroshi Doyu wrote: > > > > The disadvantage of this is that this limits the max number of streamIDs > > > > to support. If # of streamID is increased later more than 64, this > > > > format cannot cover any more. You have to predict the max # of streamIDs > > > > in advance if steamID is statically assigned. > > > > > > > > > > Well, the iommu specific binding could allow a variable #address-cells. > > > That way, you just need to know the number of stream IDs for that instance > > > of the iommu. > > > > That sounds fairly complicated to me. I don't see what that buys us over > > the clarity and simplicity that the above explicit notation gives us. Is > > it not more common for a device to have a single master rather than a > > whole bunch of them? > > I've never seen a device upstream of an ARM SMMU with a single stream-id; > they always seem to have a whole bunch of them. Calxeda's SATA controller > had 10 IDs, for example, and a PL330 DMA controller tends to have at least > 3. What are those good for? Would we just always use the first one? Arnd