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: <65e6d61a-7648-4125-8550-8a8c6d476b0a@oss.qualcomm.com>
Date: Wed, 8 Oct 2025 11:19:32 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        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>
Cc: 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 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

Konrad