On Fri, Aug 16, 2019 at 08:43:53PM +0100, Robin Murphy wrote: > On 16/08/2019 19:12, Rob Clark wrote: > >On Fri, Aug 16, 2019 at 9:58 AM Robin Murphy <robin.murphy@xxxxxxx> wrote: > >> > >>Hi Jordan, > >> > >>On 15/08/2019 16:33, Jordan Crouse wrote: > >>>On Wed, Aug 07, 2019 at 04:21:38PM -0600, Jordan Crouse wrote: > >>>>(Sigh, resend. I freaked out my SMTP server) > >>>> > >>>>This is part of an ongoing evolution for enabling split pagetable support for > >>>>arm-smmu. Previous versions can be found [1]. > >>>> > >>>>In the discussion for v2 Robin pointed out that this is a very Adreno specific > >>>>use case and that is exactly true. Not only do we want to configure and use a > >>>>pagetable in the TTBR1 space, we also want to configure the TTBR0 region but > >>>>not allocate a pagetable for it or touch it until the GPU hardware does so. As > >>>>much as I want it to be a generic concept it really isn't. > >>>> > >>>>This revision leans into that idea. Most of the same io-pgtable code is there > >>>>but now it is wrapped as an Adreno GPU specific format that is selected by the > >>>>compatible string in the arm-smmu device. > >>>> > >>>>Additionally, per Robin's suggestion we are skipping creating a TTBR0 pagetable > >>>>to save on wasted memory. > >>>> > >>>>This isn't as clean as I would like it to be but I think that this is a better > >>>>direction than trying to pretend that the generic format would work. > >>>> > >>>>I'm tempting fate by posting this and then taking some time off, but I wanted > >>>>to try to kick off a conversation or at least get some flames so I can try to > >>>>refine this again next week. Please take a look and give some advice on the > >>>>direction. > >>> > >>>Will, Robin - > >>> > >>>Modulo the impl changes from Robin, do you think that using a dedicated > >>>pagetable format is the right approach for supporting split pagetables for the > >>>Adreno GPU? > >> > >>How many different Adreno drivers would benefit from sharing it? > > > >Hypothetically everything back to a3xx, so I *could* see usefulness of > >this in qcom_iommu (or maybe even msm-iommu). OTOH maybe with > >"modularizing" arm-smmu we could re-combine qcom_iommu and arm-smmu. > > Indeed, that's certainly something I'm planning to investigate as a future > refactoring step. > > >And as a practical matter, I'm not sure if anyone will get around to > >backporting per-context pagetables as far back as a3xx. > > > >BR, > >-R > > > >>The more I come back to this, the more I'm convinced that io-pgtable > >>should focus on the heavy lifting of pagetable management - the code > >>that nobody wants to have to write at all, let alone more than once - > >>and any subtleties which aren't essential to that should be pushed back > >>into whichever callers actually care. Consider that already, literally > >>no caller actually uses an unmodified stage 1 TCR value as provided in > >>the io_pgtable_cfg. > >> > >>I feel it would be most productive to elaborate further in the form of > >>patches, so let me get right on that and try to bash something out > >>before I go home tonight... > > ...and now there's a rough WIP branch here: > > http://linux-arm.org/git?p=linux-rm.git;a=shortlog;h=refs/heads/iommu/pgtable > > I'll finish testing and polishing those patches at some point next week, > probably, but hopefully they're sufficiently illustrative for the moment. This looks great so far. I can see where the TTBR1 stuff would fit in and I like it a lot. I'll try to have some patches ready when you are done polishing. Jordan > Robin. -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
