Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753971AbaGIK6Z (ORCPT ); Wed, 9 Jul 2014 06:58:25 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:36873 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752301AbaGIK6X (ORCPT ); Wed, 9 Jul 2014 06:58:23 -0400 Date: Wed, 9 Jul 2014 11:54:41 +0100 From: Will Deacon To: Olav Haugan Cc: Mark Rutland , "devicetree@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , Arnd Bergmann , Pawel Moll , Ian Campbell , Grant Grundler , Joerg Roedel , Stephen Warren , "linux-kernel@vger.kernel.org" , Marc Zyngier , Linux IOMMU , Rob Herring , Thierry Reding , Kumar Gala , "linux-tegra@vger.kernel.org" , Cho KyongHo , Dave P Martin , "linux-arm-kernel@lists.infradead.org" , Hiroshi Doyu , "mitchelh@codeaurora.org" Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Message-ID: <20140709105441.GE9485@arm.com> References: <4545972.cM7IP1qTXQ@wuerfel> <53A4C0C9.2050908@codeaurora.org> <20140624091808.GC26013@arm.com> <53A9BC18.2090106@codeaurora.org> <20140624181150.GB4067@arm.com> <53A9EF3A.2070704@codeaurora.org> <20140625091858.GG6153@arm.com> <53ADEEDF.7060902@codeaurora.org> <20140630095220.GA25779@arm.com> <53BC95DA.1010500@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53BC95DA.1010500@codeaurora.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 09, 2014 at 02:07:38AM +0100, Olav Haugan wrote: > On 6/30/2014 2:52 AM, Will Deacon wrote: > > On Fri, Jun 27, 2014 at 11:23:27PM +0100, Olav Haugan wrote: > >> Lets say I have an IOMMU with 2 masters and 2 SMRn slots with the > >> following stream IDs coming from the masters: > >> > >> Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28 > >> Master 2: 0x30 > >> > >> To make this work I would program SMR[0] with StreamID 0x20 and mask 0xF > >> to ignore lower 4 bits. SMR[1] would just be StreamID 0x30 with mask 0x0. > >> > >> However, I could also have an IOMMU with 2 masters and 9 SMRn slots with > >> the following stream IDs: > >> > >> Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28 > >> Master 2: 0x29 > >> > >> Here I would program all SMRn and leave the mask to be 0 for all SMRn's. > >> So how do I detect when to apply a mask or not? > > > > You would aim to use the smallest number of SMRs per master possible. > > You could probably use: > > > > Master 1: SMR[0].id == 0x20, SMR[0].mask = 0x07 > > SMR[1].id == 0x28, SMR[1].mask = 0x00 > > > > Master 2: SMR[2].id == 0x29, SMR[2].mask = 0x00 > > So how does an algorithm figure this out in both my examples? The > algorithm would have to know about both (all) bus masters and their > stream IDs for a specific SMMU. If the algorithm operates on the set of > stream IDs for one bus master at a time the algorithm has no way of > knowing which bits can be ignored since it doesn't know the value of the > other stream IDs for the other bus masters and thus could potentially > create a mask that could cause a stream ID to match in two different > entries. Complete knowledge of the system topology (i.e. all bus masters) is a requirement for being able to configure the SMMU correctly if you want to guarantee that you don't have SMR aliasing issues. > >> I am not familiar with Andreas's proposal. Do you have a link? > > > > http://marc.info/?l=linux-arm-kernel&m=139110598005846&w=2 > > Unless I am mistaken the algorithm works on one bus master at a time. I > don't think that will work. IIRC, it works for densely packed SIDs on the master, so it tries to build up power-of-2 sized groups for that master then mops up the rest with individual entries. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/