From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Fri, 20 Jun 2014 18:50:51 +0100 Message-ID: <20140620175051.GE30656@arm.com> References: <1400877395-4235-1-git-send-email-thierry.reding@gmail.com> <20140617233714.GD25525@mithrandir> <20140618101439.GF32699@arm.com> <39682213.otHMo6zoRf@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <39682213.otHMo6zoRf@wuerfel> Sender: linux-kernel-owner@vger.kernel.org To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Thierry Reding , Mark Rutland , "devicetree@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , Pawel Moll , Stephen Warren , Grant Grundler , Joerg Roedel , Ian Campbell , "linux-kernel@vger.kernel.org" , Marc Zyngier , "iommu@lists.linux-foundation.org" , Rob Herring , Kumar Gala , "linux-tegra@vger.kernel.org" , Cho KyongHo , Dave P Martin , Hiroshi Doyu List-Id: devicetree@vger.kernel.org On Fri, Jun 20, 2014 at 04:53:08PM +0100, Arnd Bergmann wrote: > On Wednesday 18 June 2014 11:14:39 Will Deacon wrote: > > On Wed, Jun 18, 2014 at 12:37:16AM +0100, Thierry Reding wrote: > > - Each master has a set of fixed StreamIDs > > - StreamIDs can be remastered by adding a constant offset (this could also > > be used to describe RequesterID -> StreamID mapping) > > > > I'd hope this would be sufficient for most people. Dynamic ID assignment can > > be worked out later (I'm not even sure it belongs in this binding) and any > > mappings other than `add a constant offset' can be treated on a case-by-case > > basis. We don't want to throw the kitchen sink at a language for describing > > arbitrary transformations! > > > > > We've had similar discussions before (power sequences anyone?) where we > > > tried to come up with a generic way to describe something in device tree > > > that just didn't work out too well. Some things are better done in code, > > > so I think we should at least consider that possibility rather than > > > blindly try and force everything into device tree. > > > > If we can support 90% of SoCs with a simple DT-based description, we can > > address the corner cases as they arise. I'm not ruling our hardcoding > > topology if we have no choice, but I don't think that's a healthy place to > > start from. > > So we could use the "arm,gicv3" comaptible string for all those that > have a relatively simple mapping, and describe that mapping entirely > in DT properties, but use a different compatible string for those > SoCs that have a mapping which we can't easily describe, and then > put that into code? That doesn't sound unreasonable, but I don't think we should commit to putting things into code until they come along and we can't describe them. Will