On Tue, Jun 24, 2014 at 07:20:56PM +0100, Arnd Bergmann wrote: > On Tuesday 24 June 2014 19:11:50 Will Deacon wrote: > > On Tue, Jun 24, 2014 at 06:57:44PM +0100, Olav Haugan wrote: > > > We do describe the masked StreamID (SID) but we need to specify the mask > > > that the SMMU should apply to the incoming SIDs, right? > > > > > > We have a bus master that emits 43 unique SIDs. However, we have only 40 > > > SMMU_SMRn registers in the SMMU. So we need to mask out some of the > > > incoming SID bits so that the 43 SIDs can match one of 40 entries in the > > > SMR. > > > > Hmm, so you're talking about stream matching, right? That doesn't belong in > > the device-tree. I appreciate that the current driver does a terrible job at > > allocating the SMRs (it's bloody difficult!), but we should try to improve > > the dynamic behaviour instead of moving configuration of the SMMU out into > > device-tree, where it's inflexible at best. > > > > There have been patches previously posted by Andreas Herrmann helping here. > > I'd be glad to see them revived. > > Note that there are areas where we have in the past decided that dynamic > configuration is just too hard for the kernel to do and that we're better > off putting the configuration into DT. Pinctrl and clocks are at least > partially in that category. > > It's always best if you can get the kernel to do things in the ideal > way where that is possible, but getting there may be just not worth it. > > I have no idea where it should be for SMMU, but it's something to consider: > if you can take reasonable shortcuts by reading parts of the configuration > from DT, you may just as well do that.
I treat this in the same manner as the topology bindings we discussed previously; we should do a best-effort to configure things dynamically and solve corner-cases and quirks as special cases. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
