Messages in this thread | | | Subject | Re: [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support | From | Robin Murphy <> | Date | Fri, 16 Aug 2019 17:58:24 +0100 |
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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?
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@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/freedreno >
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