From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933749AbaE3Tu7 (ORCPT ); Fri, 30 May 2014 15:50:59 -0400 Received: from mout.kundenserver.de ([212.227.126.130]:54944 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753146AbaE3Tu5 (ORCPT ); Fri, 30 May 2014 15:50:57 -0400 From: Arnd Bergmann To: linux-arm-kernel@lists.infradead.org Cc: Rob Herring , Mark Rutland , "devicetree@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , Pawel Moll , Ian Campbell , Grant Grundler , Joerg Roedel , Stephen Warren , Will Deacon , "linux-kernel@vger.kernel.org" , Rob Herring , Marc Zyngier , Linux IOMMU , Thierry Reding , Kumar Gala , "linux-tegra@vger.kernel.org" , Cho KyongHo , Dave Martin , Hiroshi Doyu Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Fri, 30 May 2014 21:49:59 +0200 Message-ID: <5288123.eXagyPAxNq@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> <4545972.cM7IP1qTXQ@wuerfel> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V02:K0:Dwg0+Xphz8ZXH6b1JXsHtzeZyonuF/Umpc6ZKU9KlQr LNzuJ6QRtE4SmxR6D2RPxoZ+l+4bp3jYpBvEBESgMGwZ2vvZl8 pL2YwQrxkKosJzl2rEn9nOnLc/AsvLsbVjhBlL+uuBtoHgl0LV v/F27sJwR7UXCWkyf7iDvP9UlGk6jL0F3LiFoKEZxM1tHfpsKx jFGJfaL++5zloPo2tSw8kywaazEzHh/t9YS1HfX5ylrfY4BFwG KxFwEx+jfZFxa5XfLw1vCS0ENNm5UpyZTP6k7AiGcSDjayasNC +6m8uaPSgJFMcQWRx1TeulHlV5HC54nuMmUmCU98heHA5qnVwE GlYsak5hb6f7k98q9iYQ= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 30 May 2014 14:31:55 Rob Herring wrote: > On Fri, May 30, 2014 at 2:06 PM, Arnd Bergmann wrote: > > 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. > > My suggestion was that you also put the IDs in the dma-ranges as the > first cell much as ranges for PCI encodes other information in the > first cell. Then you can have an entry for each ID. The downside is > another special case like PCI. > > The argument for using #address-cells and #size-cells seems to be to > align with how ranges work. If that's the route we want to go, then I > say we should not stop there and actually use dma-ranges as well. > Otherwise, I don't see the advantage over #iommu-cells. I can see how dma-ranges in bus nodes work, it just doesn't seem to have any reasonable meaning in the iommu node itself. > > 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? > > 1 master with 7 IDs like this: > > master@a { > ... > iommus = <&smmu 0> <&smmu 1> <&smmu 2> <&smmu 3> > <&smmu 4> <&smmu 5> <&smmu 6> <&smmu 7>; > }; > > If there was any sort of window, then it is almost certainly the same > window for each ID. Ok, I see. In that case you'd probably want to have #address-cells = <1> and #size-cells = <1> and give a range of IDs like iommus = <&smmu 0 8>; Do you think that ranges can have a meaningful definition with the ARM SMMU stream IDs? Arnd