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. 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... > > Robin. > > > If so, then is adding the changes to io-pgtable-arm.c possible for 5.4 and then > > add the implementation specific code on top of Robin's stack later or do you > > feel they should come as part of a package deal? > > > > Jordan > > > >> Jordan Crouse (2): > >> iommu/io-pgtable-arm: Add support for ARM_ADRENO_GPU_LPAE io-pgtable > >> format > >> iommu/arm-smmu: Add support for Adreno GPU pagetable formats > >> > >> drivers/iommu/arm-smmu.c | 8 +- > >> drivers/iommu/io-pgtable-arm.c | 214 ++++++++++++++++++++++++++++++++++++++--- > >> drivers/iommu/io-pgtable.c | 1 + > >> include/linux/io-pgtable.h | 2 + > >> 4 files changed, 209 insertions(+), 16 deletions(-) > >> > >> -- > >> 2.7.4 > >> > >> _______________________________________________ > >> Freedreno mailing list > >> Freedreno@xxxxxxxxxxxxxxxxxxxxx > >> https://lists.freedesktop.org/mailman/listinfo/freedreno > > > _______________________________________________ > Freedreno mailing list > Freedreno@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/freedreno
