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

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Message-ID: <bylruidduy2u4lsqlhzmohahgkm633hijffi3s2wt5ojeaotk3@awulzz2qdg7h>
Date: Mon, 29 Dec 2025 22:00:02 +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 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'm fine with the change, but I think we should make sure that Gunyah
doesn't break existing device trees.

> 
> The DT changes should be backwards compatible with legacy QHEE based
> firmware stack too.
> 
> Suggested-by: Prakash Gupta <guptap@....qualcomm.com>
> Signed-off-by: Sumit Garg <sumit.garg@....qualcomm.com>
> ---
>  arch/arm64/boot/dts/qcom/agatti.dtsi | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 

-- 
With best wishes
Dmitry