From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933858AbaE3TGv (ORCPT ); Fri, 30 May 2014 15:06:51 -0400 Received: from mout.kundenserver.de ([212.227.126.130]:50067 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751525AbaE3TGs (ORCPT ); Fri, 30 May 2014 15:06:48 -0400 From: Arnd Bergmann To: Rob Herring Cc: Thierry Reding , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Cho KyongHo , Grant Grundler , Dave Martin , Marc Zyngier , Will Deacon , Joerg Roedel , Stephen Warren , Hiroshi Doyu , "devicetree@vger.kernel.org" , Linux IOMMU , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Fri, 30 May 2014 21:06:16 +0200 Message-ID: <4545972.cM7IP1qTXQ@wuerfel> User-Agent: KMail/4.11.5 (Linux/3.11.0-18-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V02:K0:Srl5ALsrqy79FBxN0HyvBfmaEfWG4IiSw2HHUAiE1fz NEoAP0/r2l56JLRH6fhivu0BPbQTY9xnAkBx5Mvwgv0fm9Vumc 5G9fZdroQ3cVsBt+CeCIv0DFuT7bhWjxdEoBiNSjw+1MXJy7VQ wJut5hMfbcw8+0c78gv0Xf/+kmPHeU4tq8ccnssLD5V8Ts0KZZ Lv6pdTQmwCaiw7+9SvWF+shfNY1AUWYr/FKGLMjVwZ5tRHbMIa ogIYGrJJSp3+qLY4HoKsaW4KD4GH1UKbP9IFIDwVC5hw34eyBL /Ac0yHNvg68yBmJUGHcnoGtvDAf5pQ3uPJakYBLgXKDdo1rLeE aUKFPizrEZcVUOUIF+zk= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 30 May 2014 08:16:05 Rob Herring wrote: > On Fri, May 23, 2014 at 3:33 PM, Thierry Reding > wrote: > > From: Thierry Reding > > +IOMMU master node: > > +================== > > + > > +Devices that access memory through an IOMMU are called masters. A device can > > +have multiple master interfaces (to one or more IOMMU devices). > > + > > +Required properties: > > +-------------------- > > +- iommus: A list of phandle and IOMMU specifier pairs that describe the IOMMU > > + master interfaces of the device. One entry in the list describes one master > > + interface of the device. > > + > > +When an "iommus" property is specified in a device tree node, the IOMMU will > > +be used for address translation. If a "dma-ranges" property exists in the > > +device's parent node it will be ignored. An exception to this rule is if the > > +referenced IOMMU is disabled, in which case the "dma-ranges" property of the > > +parent shall take effect. > > Just thinking out loud, could you have dma-ranges in the iommu node > for the case when the iommu is enabled rather than putting the DMA > window information into the iommus property? > > This would probably mean that you need both #iommu-cells and #address-cells. The reason for doing like this was that you may need a different window for each device, while there can only be one dma-ranges property in an iommu node. > > + > > +Optional properties: > > +-------------------- > > +- iommu-names: A list of names identifying each entry in the "iommus" > > + property. > > Do we really need a name here? I would not expect that you have > clearly documented names here from the datasheet like you would for > interrupts or clocks, so you'd just be making up names. Sorry, but I'm > not a fan of names properties in general. Good point, this was really overdesign by modeling it after other subsystems that can have a use for names. > > +Multiple-master IOMMU: > > +---------------------- > > + > > + iommu { > > + /* the specifier represents the ID of the master */ > > + #address-cells = <1>; > > + #size-cells = <0>; > > + }; > > + > > + master { > > + /* device has master ID 42 in the IOMMU */ > > + iommus = <&/iommu 42>; > > + }; > > Presumably the ID would be the streamID on ARM's SMMU. How would a > master with 8 streamIDs be described? This is what Calxeda midway has > for SATA and I would expect that to be somewhat common. Either you > need some ID masking or you'll have lots of duplication when you have > windows. I don't understand the problem. If you have stream IDs 0 through 7, you would have master@a { ... iommus = <&smmu 0>; }; master@b { ... iommus = <&smmu 1; }; ... master@12 { ... iommus = <&smmu 7; }; and you don't need a window at all. Why would you need a mask of some sort? Arnd