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. > >> 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. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
