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

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Message-ID: <oacyy4r7vsbpcdzripuv24djh2lgjux2danqrc3fwgbyhpgtia@njdjysybobpt>
Date: Tue, 30 Dec 2025 16:40:20 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Akhil P Oommen <akhilpo@....qualcomm.com>
Cc: Sumit Garg <sumit.garg@...nel.org>, 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, 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 06:16:05PM +0530, Akhil P Oommen wrote:
> On 12/30/2025 12:35 PM, Dmitry Baryshkov wrote:
> > 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).
> 
> But the existing DT description for Agatti GPU is buggy. SID 2 is for
> secure access from GPU and it should not be mixed with non-secure
> access. We haven't hit any issue so far because the KMD doesn't have
> support for secure usecase yet.
> 
> At least for the GPU property, I feel that the right thing to do is to
> correct the buggy description.

I do not doubt the change, we should not be mapping secure SIDs. However
I very much dislike the fact that changing the bootloader makes us
perform this change.

> 
> -Akhil
> 
> > 
> >>
> >>>
> >>> 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