linux-kernel - Re: [PATCH v9 0/7] iommu/arm-smmu: Enable split pagetable support

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Date:   Wed, 01 Jul 2020 15:41:03 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Will Deacon <will@...nel.org>
Cc:     linux-arm-msm@...r.kernel.org,
        John Stultz <john.stultz@...aro.org>,
        freedreno@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Brian Masney <masneyb@...tation.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Joerg Roedel <joro@...tes.org>,
        Rob Clark <robdclark@...il.com>,
        Rob Herring <robh+dt@...nel.org>, Sean Paul <sean@...rly.run>,
        Shawn Guo <shawn.guo@...aro.org>, Takashi Iwai <tiwai@...e.de>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH v9 0/7] iommu/arm-smmu: Enable split pagetable support

Hi Will, Robin,

On 2020-06-27 01:30, Jordan Crouse wrote:
> Another iteration of the split-pagetable support for arm-smmu and the 
> Adreno GPU
> SMMU. After email discussions [1] we opted to make a arm-smmu 
> implementation for
> specifically for the Adreno GPU and use that to enable split pagetable 
> support
> and later other implementation specific bits that we need.
> 
> On the hardware side this is very close to the same code from before 
> [2] only
> the TTBR1 quirk is turned on by the implementation and not a domain 
> attribute.
> In drm/msm we use the returned size of the aperture as a clue to let us 
> know
> which virtual address space we should use for global memory objects.
> 
> There are two open items that you should be aware of. First, in the
> implementation specific code we have to check the compatible string of 
> the
> device so that we only enable TTBR1 for the GPU (SID 0) and not the GMU 
> (SID 4).
> I went back and forth trying to decide if I wanted to use the 
> compatible string
> or the SID as the filter and settled on the compatible string but I 
> could be
> talked out of it.
> 
> The other open item is that in drm/msm the hardware only uses 49 bits 
> of the
> address space but arm-smmu expects the address to be sign extended all 
> the way
> to 64 bits. This isn't a problem normally unless you look at the 
> hardware
> registers that contain a IOVA and then the upper bits will be zero. I 
> opted to
> restrict the internal drm/msm IOVA range to only 49 bits and then sign 
> extend
> right before calling iommu_map / iommu_unmap. This is a bit wonky but I 
> thought
> that matching the hardware would be less confusing when debugging a 
> hang.
> 
> v9: Fix bot-detected merge conflict
> v7: Add attached device to smmu_domain to pass to implementation 
> specific
> functions
> 
> [1] 
> https://lists.linuxfoundation.org/pipermail/iommu/2020-May/044537.html
> [2] https://patchwork.kernel.org/patch/11482591/
> 
> 
> Jordan Crouse (7):
>   iommu/arm-smmu: Pass io-pgtable config to implementation specific
>     function
>   iommu/arm-smmu: Add support for split pagetables
>   dt-bindings: arm-smmu: Add compatible string for Adreno GPU SMMU
>   iommu/arm-smmu: Add a pointer to the attached device to smmu_domain
>   iommu/arm-smmu: Add implementation for the adreno GPU SMMU
>   drm/msm: Set the global virtual address range from the IOMMU domain
>   arm: dts: qcom: sm845: Set the compatible string for the GPU SMMU
> 
>  .../devicetree/bindings/iommu/arm,smmu.yaml   |  4 ++
>  arch/arm64/boot/dts/qcom/sdm845.dtsi          |  2 +-
>  drivers/gpu/drm/msm/adreno/adreno_gpu.c       | 13 +++++-
>  drivers/gpu/drm/msm/msm_iommu.c               |  7 +++
>  drivers/iommu/arm-smmu-impl.c                 |  6 ++-
>  drivers/iommu/arm-smmu-qcom.c                 | 45 ++++++++++++++++++-
>  drivers/iommu/arm-smmu.c                      | 38 +++++++++++-----
>  drivers/iommu/arm-smmu.h                      | 30 ++++++++++---
>  8 files changed, 120 insertions(+), 25 deletions(-)

Any chance reviewing this?

Thanks,
Sai

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