From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olav Haugan Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Date: Thu, 10 Jul 2014 15:32:16 -0700 Message-ID: <53BF1470.1000704@codeaurora.org> References: <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> <20140630095220.GA25779@arm.com> <53BC95DA.1010500@codeaurora.org> <20140709105441.GE9485@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140709105441.GE9485-5wv7dgnIgG8@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: Will Deacon Cc: Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Arnd Bergmann , Pawel Moll , Ian Campbell , Grant Grundler , 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" List-Id: devicetree@vger.kernel.org On 7/9/2014 3:54 AM, Will Deacon wrote: > On Wed, Jul 09, 2014 at 02:07:38AM +0100, Olav Haugan wrote: >> On 6/30/2014 2:52 AM, Will Deacon wrote: >>> On Fri, Jun 27, 2014 at 11:23:27PM +0100, Olav Haugan wrote: >>>> 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 >> >> 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. >>>> 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. 2) Same Stream IDs but only 2 SMRs. The algorithm gave an error saying I did not have enough SMRs. Thanks, Olav -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation