From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: Question about arm smmu Date: Wed, 4 Nov 2015 15:31:55 +0000 Message-ID: <563A24EB.6090106@arm.com> References: <20151104134439.GA4022@linux-4gyl.site> <20151104144308.GQ5405@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20151104144308.GQ5405-5wv7dgnIgG8@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 , Peng Fan Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: iommu@lists.linux-foundation.org On 04/11/15 14:43, Will Deacon wrote: > On Wed, Nov 04, 2015 at 09:44:40PM +0800, Peng Fan wrote: >> Hi Will, > > Hello, > >> I am trying to enable SMMU(mmu500) on an platform. >> My platform support only 32 SIDs, but it have more than 100 masters. Do you mean the MMU-500 configuration really only has 5 bits of stream ID wired up (which seems a bit unlikely, especially given that in such a configuration you should gain extra bits from the prepended TBU number), or that you have a sufficient number of stream ID bits but only have 32 stream matching groups? >> So I need to let different masters share one SID. I read current >> arm-smmu.c, but it needs each master has unique SID. Do you have >> some suggestions about how to let different masters sharing one >> SID? > > We can achieve that using iommu_groups, but then we need a way to > describe those groups in the device-tree, as opposed to putting > each device into its own group like we do at present. Robin (CC'd) had > some work-in-progress for this, iirc. I spent enough time on it that I reached the point of thinking there's no feasible DT binding that is sufficiently hardware-agnostic, and isn't just trying to paint a Linux implementation detail as hardware description - the master IDs are already there, so it might as well be up to the thing parsing them to work out what, if anything, it wants to do with duplicates. What I have now is a simple little lookup table solution inside the SMMUv2 driver to automatically track groups by stream ID for platform devices. I've not yet tried pulling in Joerg's generic group series, but I think it's going to slot together really neatly with that, so I might try breaking it out of the big stream ID probing rework I'm currently half-way through. >> On my platform, SID can be dynamically programmed. So I can program >> DMA0 and DMA1 using one SID, saying 0x5. But I do not have a good >> idea how to support this use case in arm-smmu.c driver. > > I think we've have the firmware allocating the SIDs, then describing > the grouping to Linux in the device-tree. Yeah, regardless of how we handle groups we need the SIDs to be in the DT and not change at runtime, so the programming is going to have to be done before the kernel even runs. Robin. > > Will >