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: Fri, 30 May 2014 21:01:19 +0200 Message-ID: <4830064.JvgTAs8Xty@wuerfel> References: <1400877395-4235-1-git-send-email-thierry.reding@gmail.com> <20140530112226.GA3949@e103592.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140530112226.GA3949-M5GwZQ6tE7x5pKCnmE3YQBJ8xKzm50AiAL8bYrjMMd8@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: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Cc: Mark Rutland , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Pawel Moll , Ian Campbell , Grant Grundler , Stephen Warren , Will Deacon , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Rob Herring , Marc Zyngier , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Thierry Reding , Kumar Gala , linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Cho KyongHo , Dave Martin List-Id: linux-tegra@vger.kernel.org On Friday 30 May 2014 12:22:32 Dave Martin wrote: > > + > > +Examples: > > +========= > > + > > +Single-master IOMMU: > > +-------------------- > > + > > + iommu { > > + #address-cells = <0>; > > + #size-cells = <0>; > > + }; > > + > > + master { > > + iommus = <&/iommu>; > > + }; > > + > > +Multiple-master IOMMU with fixed associations: > > +---------------------------------------------- > > + > > + /* multiple-master IOMMU */ > > + iommu { > > + /* > > + * Masters are statically associated with this IOMMU and > > + * address translation is always enabled. > > + */ > > + #address-cells = <0>; > > + #size-cells = <0>; > > In this example, can different translations be set up for the different > masters? > > With no cells available to contain any sort of ID, it looks like this > is not possible. Correct, this example is for an IOMMU that does not use IDs but has a shared address space for all devices. > > +Multiple-master IOMMU with configurable DMA window: > > +--------------------------------------------------- > > + > > + / { > > + #address-cells = <1>; > > + #size-cells = <1>; > > + > > + iommu { > > + /* master ID, address of DMA window */ > > + #address-cells = <2>; > > + #size-cells = <2>; > > + }; > > + > > + master { > > + /* master ID 42, 4 GiB DMA window starting at 0 */ > > + iommus = <&/iommu 42 0 0x1 0x0>; > > I'm still concerned that in order to deal with future cases we will have > to invent multiple ways to parse the "iommus" property. For example, if > we have a PCEe RC mastering through an IOMMU, it will pass a huge set > of possible master IDs to the IOMMU, not just noe or two. > > Do you have a solution in mind for that which doesn't break backwards > compatibility? I think we can treat PCI as a special case here and have an interface that gets used by the PCI core code to talk to the IOMMU core code when setting up a the dma_map_ops for a PCI function. As long as the IOMMU driver understands what PCI is, we don't have to describe the mapping in detail. > One option is to include an extra cell to the IOMMUs property > that indicates how to parse it. For now, only a single value would > be defined. For example: > > iommus = <&/iommu IOMMU_SIMPLE 42>; > > Then maybe later > > iommus = <&/iommu IOMMU_RANGE 0x10000 0x10000>; > > (I'm not suggesting what IOMMU_RANGE might mean.) > This can really be left up to the specific IOMMU driver itself. We can have drivers that support both #address-cells=<1> and #address-cells=<2> and behave differently based on that. I don't see a reason to define that across IOMMU implementations. > Other options are to introduce a new property name > > range-iommus = <&/iommu 0x10000 0x10000>; > > or control the parsing of incompatible iommus properties via a compatible > string somewhere. Introducing a new compatible string is always an option as the last resort. Arnd