From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Fri, 20 Jun 2014 17:53:08 +0200 Message-ID: <39682213.otHMo6zoRf@wuerfel> References: <1400877395-4235-1-git-send-email-thierry.reding@gmail.com> <20140617233714.GD25525@mithrandir> <20140618101439.GF32699@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140618101439.GF32699-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Cc: Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Pawel Moll , Stephen Warren , Grant Grundler , Ian Campbell , Will Deacon , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Rob Herring , Marc Zyngier , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , Thierry Reding , Kumar Gala , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Cho KyongHo , Dave P Martin List-Id: devicetree@vger.kernel.org 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? Arnd