From: Robin Murphy <robin.murphy@arm.com>
To: freedreno@lists.freedesktop.org, Rob Herring <robh@kernel.org>,
Will Deacon <will@kernel.org>,
jean-philippe.brucker@arm.com, linux-arm-msm@vger.kernel.org,
Joerg Roedel <joro@8bytes.org>,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Zhen Lei <thunder.leizhen@huawei.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support
Date: Fri, 16 Aug 2019 17:58:24 +0100 [thread overview]
Message-ID: <ac248f33-2528-c1d4-17ed-17e92e6ed5ad@arm.com> (raw)
In-Reply-To: <20190815153304.GD28465@jcrouse1-lnx.qualcomm.com>
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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next prev parent reply other threads:[~2019-08-16 16:58 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 22:21 [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support Jordan Crouse
2019-08-07 22:21 ` [PATCH v3 1/2] iommu/io-pgtable-arm: Add support for ARM_ADRENO_GPU_LPAE io-pgtable format Jordan Crouse
2019-08-15 15:35 ` Jordan Crouse
2019-08-07 22:21 ` [PATCH v3 2/2] iommu/arm-smmu: Add support for Adreno GPU pagetable formats Jordan Crouse
2019-08-15 15:33 ` [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support Jordan Crouse
2019-08-16 16:58 ` Robin Murphy [this message]
2019-08-16 18:12 ` Rob Clark
2019-08-16 19:43 ` Robin Murphy
2019-08-16 22:20 ` Jordan Crouse
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