linux-kernel - Re: [PATCH v4 11/12] remoteproc: qcom: pas: Enable Secure PAS support with IOMMU managed by Linux

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Message-ID: <20251008120010.kygbso4vw2ouwlzu@hu-mojha-hyd.qualcomm.com>
Date: Wed, 8 Oct 2025 17:30:10 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 11/12] remoteproc: qcom: pas: Enable Secure PAS
 support with IOMMU managed by Linux

On Wed, Oct 08, 2025 at 11:19:32AM +0200, Konrad Dybcio wrote:
> On 10/7/25 6:48 PM, Mukesh Ojha wrote:
> > Most Qualcomm platforms feature Gunyah hypervisor, which typically
> > handles IOMMU configuration. This includes mapping memory regions and
> > device memory resources for remote processors by intercepting
> > qcom_scm_pas_auth_and_reset() calls. These mappings are later removed
> > during teardown. Additionally, SHM bridge setup is required to enable
> > memory protection for both remoteproc metadata and its memory regions.
> > When the aforementioned hypervisor is absent, the operating system must
> > perform these configurations instead.
> > 
> > When Linux runs as the hypervisor (@ EL2) on a SoC, it will have its
> > own device tree overlay file that specifies the firmware stream ID now
> > managed by Linux for a particular remote processor. If the iommus
> > property is specified in the remoteproc device tree node, it indicates
> > that IOMMU configuration must be handled by Linux. In this case, the
> > has_iommu flag is set for the remote processor, which ensures that the
> > resource table, carveouts, and SHM bridge are properly configured before
> > memory is passed to TrustZone for authentication. Otherwise, the
> > has_iommu flag remains unset, which indicates default behavior.
> > 
> > Enables Secure PAS support for remote processors when IOMMU configuration
> > is managed by Linux.
> > 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> > ---
> 
> [...]
> 
> > +	if (of_property_present(pdev->dev.of_node, "iommus")) {
> > +		struct of_phandle_args args;
> > +
> > +		ret = of_parse_phandle_with_args(pdev->dev.of_node, "iommus",
> > +						 "#iommu-cells", 0, &args);
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		rproc->has_iommu = true;
> > +		of_node_put(args.np);
> > +	} else {
> > +		rproc->has_iommu = false;
> > +	}
> 
> I think the above is a little heavy-handed..
> 
> rproc->has_iommu = of_property_present(...)
> 
> should suffice.. if the developer puts something that isn't a #xxx-cells
> -marked provider in xxx = <>, that's on them

Sure.

> 
> Konrad

-- 
-Mukesh Ojha