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

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Message-ID: <aVNf-lZ1KcH3tRV_@sumit-xelite>
Date: Tue, 30 Dec 2025 10:45:38 +0530
From: Sumit Garg <sumit.garg@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
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 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.

> 
> 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.

-Sumit

> 
> > 
> > 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
>