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 -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
