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
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