linux-kernel - Re: [PATCH 1/2] arm64: dts: qcom: agatti: Fix IOMMU DT properties

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Message-ID: <yudvagpfw3tfemvf3wcr62jrlvxfo5yobgsrzj4nechtqdxeu6@i2pfy4ys6qlj>
Date: Tue, 30 Dec 2025 09:05:28 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Sumit Garg <sumit.garg@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        andersson@...nel.org, konradybcio@...nel.org, robh@...nel.org,
        krzk+dt@...nel.org, conor+dt@...nel.org, akhilpo@....qualcomm.com,
        vikash.garodia@....qualcomm.com, dikshita.agarwal@....qualcomm.com,
        robin.clark@....qualcomm.com, lumag@...nel.org,
        linux-kernel@...r.kernel.org, Sumit Garg <sumit.garg@....qualcomm.com>,
        Prakash Gupta <guptap@....qualcomm.com>
Subject: Re: [PATCH 1/2] arm64: dts: qcom: agatti: Fix IOMMU DT properties

On Tue, Dec 30, 2025 at 10:45:38AM +0530, Sumit Garg wrote:
> On Mon, Dec 29, 2025 at 10:00:02PM +0200, Dmitry Baryshkov wrote:
> > On Mon, Dec 29, 2025 at 12:42:57PM +0530, Sumit Garg wrote:
> > > From: Sumit Garg <sumit.garg@....qualcomm.com>
> > > 
> > > Fix IOMMU DT propeties for GPU, display and video peripherals via
> > > dropping SMMU stream IDs which relates to secure context bank.
> > > 
> > > This problem only surfaced when the Gunyah based firmware stack is
> > > ported on Agatti replacing the legacy QHEE based firmware stack. Assigning
> > > Linux kernel (HLOS) VMID to secure context bank stream IDs is treated
> > > as a fault by Gunyah hypervisor which were previously ignored by QHEE
> > > hypervisor.
> > 
> > We are porting the underlaying layer. Can we make it to behave in a way
> > similar to the _existing_ software? If DT was a part of the firmware, it
> > would have been fine to perform such updates. But as it is not, we
> > really should try not to break the interface boundary between firmware
> > and the kernel.
> 
> I support your viewpoint. But in this current case Linux kernel VMID mapping
> for secure context bank stream IDs is incorrect. As Konrad mentioned in the
> other thread that for secure media streaming use-cases, it rather requires
> proper representation via iommu-map such that appropriate VMID can be mapped.

Yes, I understand this part. I'm basically suggesting that Gunyah should
ignore this SID when programming the actual SMMU (probably like QHEE
did).

> 
> > 
> > I'm fine with the change, but I think we should make sure that Gunyah
> > doesn't break existing device trees.
> 
> Sure, this change isn't breaking any DT ABI but brings compliance to
> usage of stream IDs.

Actually, it does, as you can see from Rob's email. You didn't perform
make dtbs_check while submitting this patch.

-- 
With best wishes
Dmitry