linux-kernel - Re: [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable support

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Message-ID: <20190815153304.GD28465@jcrouse1-lnx.qualcomm.com>
Date:   Thu, 15 Aug 2019 09:33:04 -0600
From:   Jordan Crouse <jcrouse@...eaurora.org>
To:     freedreno@...ts.freedesktop.org
Cc:     Rob Herring <robh@...nel.org>, Will Deacon <will@...nel.org>,
        jean-philippe.brucker@....com, linux-arm-msm@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org,
        Zhen Lei <thunder.leizhen@...wei.com>, robin.murphy@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [Freedreno] [PATCH v3 0/2] iommu/arm-smmu: Split pagetable
 support

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?

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@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/freedreno

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