linux-kernel - Re: [PATCH v2 10/11] remoteproc: qcom: pas: Enable Secure PAS support with IOMMU managed by Linux

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Message-ID: <aKWJ-c6B5Pvjw_jx@linaro.org>
Date: Wed, 20 Aug 2025 10:40:25 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Vikash Garodia <quic_vgarodia@...cinc.com>,
	Dikshita Agarwal <quic_dikshita@...cinc.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Abhinav Kumar <abhinav.kumar@...ux.dev>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-media@...r.kernel.org, linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v2 10/11] remoteproc: qcom: pas: Enable Secure PAS
 support with IOMMU managed by Linux

On Tue, Aug 19, 2025 at 10:24:45PM +0530, Mukesh Ojha wrote:
> Most Qualcomm platforms feature a proprietary hypervisor (such as Gunyah
> or QHEE), 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 (at 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 is the 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>
> ---
>  drivers/remoteproc/qcom_q6v5_pas.c | 63 +++++++++++++++++++++++++++---
>  1 file changed, 57 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/remoteproc/qcom_q6v5_pas.c b/drivers/remoteproc/qcom_q6v5_pas.c
> index 1e0f09bf1ef2..180528bcd57c 100644
> --- a/drivers/remoteproc/qcom_q6v5_pas.c
> +++ b/drivers/remoteproc/qcom_q6v5_pas.c
> [...]
> @@ -424,7 +459,8 @@ static int qcom_pas_parse_firmware(struct rproc *rproc, const struct firmware *f
>  	if (!rproc->has_iommu)
>  		return ret;
>  
> -	ret = qcom_scm_pas_get_rsc_table(pas->pas_id, NULL, 0, &output_rt, &output_rt_size);
> +	ret = qcom_scm_pas_get_rsc_table(pas->pas_ctx, NULL, 0,
> +					 &output_rt, &output_rt_size);

Unrelated formatting change, should be in previous commit.

>  	if (ret) {
>  		dev_err(pas->dev, "error %d getting resource_table\n", ret);
>  		return ret;
> @@ -726,6 +762,20 @@ static int qcom_pas_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  	}
>  
> +	if (of_property_present(pdev->dev.of_node, "iommus")) {

I think you need a dt-bindings change for this? You had one in v1, but
dropped it entirely for some reason.

> +		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;
> +	}
> +
>  	rproc->auto_boot = desc->auto_boot;
>  	rproc_coredump_set_elf_info(rproc, ELFCLASS32, EM_NONE);
>  
> @@ -800,6 +850,7 @@ static int qcom_pas_probe(struct platform_device *pdev)
>  	if (!pas->dtb_pas_ctx)
>  		goto remove_ssr_sysmon;
>  
> +	pas->pas_ctx->has_iommu = pas->dtb_pas_ctx->has_iommu = rproc->has_iommu;

Nitpick: I think this would look cleaner if you separate it into two
lines (only one assignment on each line).

Thanks,
Stephan