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: Mon, 30 Jun 2014 10:52:20 +0100 Message-ID: <20140630095220.GA25779@arm.com> References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <53ADEEDF.7060902-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Olav Haugan Cc: Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Arnd Bergmann , Pawel Moll , Ian Campbell , Grant Grundler , Joerg Roedel , Stephen Warren , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Marc Zyngier , Linux IOMMU , Rob Herring , Thierry Reding , Kumar Gala , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Cho KyongHo , Dave P Martin , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Hiroshi List-Id: devicetree@vger.kernel.org Hi Olav, On Fri, Jun 27, 2014 at 11:23:27PM +0100, Olav Haugan wrote: > On 6/25/2014 2:18 AM, Will Deacon wrote: > > Why can't it be dynamically detected? Whilst the StreamIDs are fixed in > > hardware (from the SMMU architecture perspective), the SMRs are completely > > programmable. Why doesn't something like Andreas's proposal work for you? > > The idea there was to find the constant bits among the StreamIDs for a > > master and create the mask accordingly. > > > 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 > I am not familiar with Andreas's proposal. Do you have a link? http://marc.info/?l=linux-arm-kernel&m=139110598005846&w=2 Note that since Calxeda went under, Andreas is unfortunately no longer working on this. Will