Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753239AbaGKMYW (ORCPT ); Fri, 11 Jul 2014 08:24:22 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:38342 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751071AbaGKMYT (ORCPT ); Fri, 11 Jul 2014 08:24:19 -0400 Date: Fri, 11 Jul 2014 13:24:25 +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 , "mitchelh@codeaurora.org" , Dave P Martin , "linux-arm-kernel@lists.infradead.org" , Hiroshi Doyu Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Message-ID: <20140711122425.GD12899@arm.com> References: <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> <20140709105441.GE9485@arm.com> <53BF1470.1000704@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53BF1470.1000704@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 Thu, Jul 10, 2014 at 11:32:16PM +0100, Olav Haugan wrote: > On 7/9/2014 3:54 AM, Will Deacon wrote: > > On Wed, Jul 09, 2014 at 02:07:38AM +0100, Olav Haugan wrote: > >> 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. > > So you agree that an algorithm needs to know about all the bus > masters/stream IDs for a specific IOMMU before it can figure out the > StreamID masks and how many SMRs can be allocated to a specific bus > master? Andreas's algorithm does not know about the other bus > masters/stream IDs. It operates on one bus master at a time. Right, but it can certainly be improved. There are certain things you can do without complete knowledge, as I mentioned previously (if you can have densely packed power-of-2 aligned/sized regions). > >>>> 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. > > I ran the algorithm through a few trivial cases: > > 1) > Stream IDs: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28 > Number of SMRs: 9 > > In this case the algorithm decided to set mask to 0 for all entries > using up 8 of the SMRs. Well think about what it's doing... we don't know about SID 0x20, for example so there's not much it can do. > 2) Same Stream IDs but only 2 SMRs. > The algorithm gave an error saying I did not have enough SMRs. There's a reason this didn't get merged, and it would be great if you could try to improve the situation ;). 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/