Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755606AbaFYJRJ (ORCPT ); Wed, 25 Jun 2014 05:17:09 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:34063 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752529AbaFYJRE (ORCPT ); Wed, 25 Jun 2014 05:17:04 -0400 Date: Wed, 25 Jun 2014 10:17:02 +0100 From: Will Deacon To: Arnd Bergmann Cc: Olav Haugan , Rob Herring , Mark Rutland , "devicetree@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , 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 Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Message-ID: <20140625091702.GF6153@arm.com> References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> <53A9BC18.2090106@codeaurora.org> <20140624181150.GB4067@arm.com> <4855051.rhxSrNMNLg@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4855051.rhxSrNMNLg@wuerfel> 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 Tue, Jun 24, 2014 at 07:20:56PM +0100, Arnd Bergmann wrote: > On Tuesday 24 June 2014 19:11:50 Will Deacon wrote: > > On Tue, Jun 24, 2014 at 06:57:44PM +0100, Olav Haugan wrote: > > > We do describe the masked StreamID (SID) but we need to specify the mask > > > that the SMMU should apply to the incoming SIDs, right? > > > > > > We have a bus master that emits 43 unique SIDs. However, we have only 40 > > > SMMU_SMRn registers in the SMMU. So we need to mask out some of the > > > incoming SID bits so that the 43 SIDs can match one of 40 entries in the > > > SMR. > > > > Hmm, so you're talking about stream matching, right? That doesn't belong in > > the device-tree. I appreciate that the current driver does a terrible job at > > allocating the SMRs (it's bloody difficult!), but we should try to improve > > the dynamic behaviour instead of moving configuration of the SMMU out into > > device-tree, where it's inflexible at best. > > > > There have been patches previously posted by Andreas Herrmann helping here. > > I'd be glad to see them revived. > > Note that there are areas where we have in the past decided that dynamic > configuration is just too hard for the kernel to do and that we're better > off putting the configuration into DT. Pinctrl and clocks are at least > partially in that category. > > It's always best if you can get the kernel to do things in the ideal > way where that is possible, but getting there may be just not worth it. > > I have no idea where it should be for SMMU, but it's something to consider: > if you can take reasonable shortcuts by reading parts of the configuration > from DT, you may just as well do that. I treat this in the same manner as the topology bindings we discussed previously; we should do a best-effort to configure things dynamically and solve corner-cases and quirks as special cases. 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/