linux-kernel - Re: [PATCH v8 11/14] firmware: qcom_scm: Add qcom_scm_pas_get_rsc

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Message-ID: <20251124152538.wt3kzztqmpr76hsx@hu-mojha-hyd.qualcomm.com>
Date: Mon, 24 Nov 2025 20:55:38 +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 v8 11/14] firmware: qcom_scm: Add
 qcom_scm_pas_get_rsc_table() to get resource table

On Mon, Nov 24, 2025 at 12:48:31PM +0100, Konrad Dybcio wrote:
> On 11/21/25 12:01 PM, Mukesh Ojha wrote:
> > Qualcomm remote processor may rely on Static and Dynamic resources for
> > it to be functional. Static resources are fixed like for example,
> > memory-mapped addresses required by the subsystem and dynamic
> > resources, such as shared memory in DDR etc., are determined at
> > runtime during the boot process.
> > 
> > For most of the Qualcomm SoCs, when run with Gunyah or older QHEE
> > hypervisor, all the resources whether it is static or dynamic, is
> > managed by the hypervisor. Dynamic resources if it is present for a
> > remote processor will always be coming from secure world via SMC call
> > while static resources may be present in remote processor firmware
> > binary or it may be coming qcom_scm_pas_get_rsc_table() SMC call along
> > with dynamic resources.
> > 
> > Some of the remote processor drivers, such as video, GPU, IPA, etc., do
> > not check whether resources are present in their remote processor
> > firmware binary. In such cases, the caller of this function should set
> > input_rt and input_rt_size as NULL and zero respectively. Remoteproc
> > framework has method to check whether firmware binary contain resources
> > or not and they should be pass resource table pointer to input_rt and
> > resource table size to input_rt_size and this will be forwarded to
> > TrustZone for authentication. TrustZone will then append the dynamic
> > resources and return the complete resource table in output_rt
> > 
> > More about documentation on resource table format can be found in
> > include/linux/remoteproc.h
> > 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> > ---
> 
> [...]
> 
> > +int qcom_scm_pas_get_rsc_table(struct qcom_scm_pas_context *ctx, void *input_rt,
> > +			       size_t input_rt_size, void **output_rt,
> > +			       size_t *output_rt_size)
> > +{
> > +	unsigned int retry_num = 5;
> > +	int ret;
> > +
> > +	do {
> > +		*output_rt = kzalloc(*output_rt_size, GFP_KERNEL);
> > +		if (!*output_rt)
> > +			return -ENOMEM;
> > +
> > +		ret = __qcom_scm_pas_get_rsc_table(ctx->pas_id, input_rt,
> > +						   input_rt_size, output_rt,
> > +						   output_rt_size);
> > +		if (ret)
> > +			kfree(*output_rt);
> > +
> > +	} while (ret == -EAGAIN && --retry_num);
> 
> Will firmware return -EAGAIN as a result, or is this to handle the
> "buffer too small case"?

The latter one where a re-attempt could pass..

> 
> I think the latter should use a different errno (EOVERFLOW?) and print
> a message since we decided that it's the caller that suggests a suitable
> output buffer size

Agree with error code..

This is kept on the caller side keeping future in mind. where we can have
resource table coming from the client and it needs to go to TZ for
authentication.

Are you suggesting to move this retry on the caller side ?

Just for information, once video patches becomes ready, we may bring this
qcom_mdt_pas_map_devmem_rscs()[1] helper for video or any other client
should be do this here as well ?

I wanted to optimize this path, where caller is making a guess and
gets the updated output size in return.

[1]
https://lore.kernel.org/lkml/20250819165447.4149674-9-mukesh.ojha@oss.qualcomm.com/#t

> 
> In case it doesn't make sense for the caller to share their expectations,
> the buffer could be allocated (and perhaps resized if necessary) internally
> with some validation (i.e. a rsctable likely won't be 5 GiB)

Are you saying output_size as well should be checked and it should not be
greater than something like UINT_MAX or something.. ?

+	*output_rt_size = res.result[2];


> 
> Konrad

-- 
-Mukesh Ojha