Message-ID: <20251208164926.cwe7arncr6tnan5f@hu-mojha-hyd.qualcomm.com>
Date: Mon, 8 Dec 2025 22:19:26 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: 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 Fri, Dec 05, 2025 at 04:40:51PM -0600, Bjorn Andersson wrote:
> On Fri, Nov 21, 2025 at 04:31:13PM +0530, 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>
> > ---
> >  drivers/firmware/qcom/qcom_scm.c       | 158 +++++++++++++++++++++++++++++++++
> >  drivers/firmware/qcom/qcom_scm.h       |   1 +
> >  include/linux/firmware/qcom/qcom_scm.h |   4 +
> >  3 files changed, 163 insertions(+)
> > 
> > diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> > index 84498d0d2f0c..c4420b79fb57 100644
> > --- a/drivers/firmware/qcom/qcom_scm.c
> > +++ b/drivers/firmware/qcom/qcom_scm.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/of_reserved_mem.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/reset-controller.h>
> > +#include <linux/remoteproc.h>
> >  #include <linux/sizes.h>
> >  #include <linux/types.h>
> >  
> > @@ -111,6 +112,10 @@ enum qcom_scm_qseecom_tz_cmd_info {
> >  	QSEECOM_TZ_CMD_INFO_VERSION		= 3,
> >  };
> >  
> > +enum qcom_scm_rsctable_resp_type {
> > +	RSCTABLE_BUFFER_NOT_SUFFICIENT		= 20,
> > +};
> > +
> >  #define QSEECOM_MAX_APP_NAME_SIZE		64
> >  #define SHMBRIDGE_RESULT_NOTSUPP		4
> >  
> > @@ -766,6 +771,159 @@ int qcom_scm_pas_mem_setup(u32 pas_id, phys_addr_t addr, phys_addr_t size)
> >  }
> >  EXPORT_SYMBOL_GPL(qcom_scm_pas_mem_setup);
> >  
> > +static int __qcom_scm_pas_get_rsc_table(u32 pas_id, void *input_rt, size_t input_rt_size,
> > +					void **output_rt, size_t *output_rt_size)
> 
> output_rt is not going to be modified, only its content, so it can be
> void * (single pointer).
> 
> > +{
> > +	struct qcom_scm_desc desc = {
> > +		.svc = QCOM_SCM_SVC_PIL,
> > +		.cmd = QCOM_SCM_PIL_PAS_GET_RSCTABLE,
> > +		.arginfo = QCOM_SCM_ARGS(5, QCOM_SCM_VAL, QCOM_SCM_RO, QCOM_SCM_VAL,
> > +					 QCOM_SCM_RW, QCOM_SCM_VAL),
> > +		.args[0] = pas_id,
> > +		.owner = ARM_SMCCC_OWNER_SIP,
> > +	};
> > +	void *input_rt_buf, *output_rt_buf;
> 
> I do one prefer one variable per line, preferably in reverse xmas order.

Ack.

> 
> > +	struct resource_table *rsc;
> 
> Calling this "empty_rsc" will make its purpose obvious.

Ack.

> 
> > +	struct qcom_scm_res res;
> > +	int ret;
> > +
> > +	ret = qcom_scm_clk_enable();
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = qcom_scm_bw_enable();
> > +	if (ret)
> > +		goto disable_clk;
> > +
> > +	/*
> > +	 * TrustZone can not accept buffer as NULL value as argument Hence,
> > +	 * we need to pass a input buffer indicating that subsystem firmware
> > +	 * does not have resource table by filling resource table structure.
> > +	 */
> > +	if (!input_rt)
> > +		input_rt_size = sizeof(*rsc);
> 
> If you overwrite input_rt here, you don't need to repeat this
> conditional below, like:
> 
> 	struct resource_table empty_rsc = {};
> 	
> 	...
> 	
> 	if (!input_rt) {
> 		input_rt = &empty_rsc;
> 		input_rt_size = sizeof(rsc);
> 	}
> 	
> 	qcom_tzmem_alloc(input_rt_size)
> 	
> 	memcpy(input_rt_buf, input_rt);

Ack.

> 
> > +
> > +	input_rt_buf = qcom_tzmem_alloc(__scm->mempool, input_rt_size, GFP_KERNEL);
> > +	if (!input_rt_buf) {
> > +		ret = -ENOMEM;
> > +		goto disable_scm_bw;
> > +	}
> > +
> > +	if (!input_rt) {
> > +		rsc = input_rt_buf;
> > +		rsc->num = 0;
> > +	} else {
> > +		memcpy(input_rt_buf, input_rt, input_rt_size);
> > +	}
> > +
> 
> Reading this patch once more, it looks reasonable, but few of the things
> in this function actually depend on *output_rt_size, yet we perform them
> in the loop below.
> 
> We're expecting, with some certainty, that this sequence will be called
> more than once, so I think it would be preferable to slice this
> differently, and only repeat the <loop></loop> part.
> 
> <loop>

Ack, I will move all the clock, bw voting and mentioned retry(on -EOVERFLOW) loop
to the caller of this function.

> 
> > +	output_rt_buf = qcom_tzmem_alloc(__scm->mempool, *output_rt_size, GFP_KERNEL);
> > +	if (!output_rt_buf) {
> > +		ret = -ENOMEM;
> > +		goto free_input_rt_buf;
> > +	}
> > +
> > +	desc.args[1] = qcom_tzmem_to_phys(input_rt_buf);
> > +	desc.args[2] = input_rt_size;
> > +	desc.args[3] = qcom_tzmem_to_phys(output_rt_buf);
> > +	desc.args[4] = *output_rt_size;
> > +
> > +	/*
> > +	 * Whether SMC fail or pass, res.result[2] will hold actual resource table
> > +	 * size.
> > +	 *
> > +	 * if passed 'output_rt_size' buffer size is not sufficient to hold the
> > +	 * resource table TrustZone sends, response code in res.result[1] as
> > +	 * RSCTABLE_BUFFER_NOT_SUFFICIENT so that caller can retry this SMC call with
> > +	 * output_rt buffer with res.result[2] size.
> > +	 */
> > +	ret = qcom_scm_call(__scm->dev, &desc, &res);
> > +	*output_rt_size = res.result[2];
> > +	if (!ret)
> > +		memcpy(*output_rt, output_rt_buf, *output_rt_size);
> > +
> > +	if (ret && res.result[1] == RSCTABLE_BUFFER_NOT_SUFFICIENT)
> > +		ret = -EAGAIN;
> 
> </loop>
> 
> > +
> > +	qcom_tzmem_free(output_rt_buf);
> > +
> > +free_input_rt_buf:
> > +	qcom_tzmem_free(input_rt_buf);
> > +
> > +disable_scm_bw:
> > +	qcom_scm_bw_disable();
> > +
> > +disable_clk:
> > +	qcom_scm_clk_disable();
> > +
> > +	return ret ? : res.result[0];
> 
> Is there a risk that res.result[0] will carry something meaningful to
> the caller (which will be misinterpreted)?

No, its just to align with other SMC call, it will always have 0 value
on success.

> 
> > +}
> > +
> > +/**
> > + * qcom_scm_pas_get_rsc_table() - Retrieve the resource table in passed output buffer
> > + *				  for a given peripheral.
> > + *
> > + * Qualcomm remote processor may rely on both static and dynamic resources for
> > + * its functionality. Static resources typically refer to memory-mapped addresses
> > + * required by the subsystem and are often embedded within the firmware binary
> > + * and dynamic resources, such as shared memory in DDR etc., are determined at
> > + * runtime during the boot process.
> > + *
> > + * On Qualcomm Technologies devices, it's possible that static resources are not
> > + * embedded in the firmware binary and instead are provided by TrustZone However,
> > + * dynamic resources are always expected to come from TrustZone. This indicates
> > + * that for Qualcomm devices, all resources (static and dynamic) will be provided
> > + * by TrustZone via the SMC call.
> > + *
> > + * If the remote processor firmware binary does contain static resources, they
> > + * should be passed in input_rt. These will be forwarded to TrustZone for
> > + * authentication. TrustZone will then append the dynamic resources and return
> > + * the complete resource table in output_rt.
> > + *
> > + * If the remote processor firmware binary does not include a resource table,
> > + * the caller of this function should set input_rt as NULL and input_rt_size
> > + * as zero respectively.
> > + *
> > + * More about documentation on resource table data structures can be found in
> > + * include/linux/remoteproc.h
> > + *
> > + * @ctx:	    PAS context
> > + * @pas_id:	    peripheral authentication service id
> > + * @input_rt:       resource table buffer which is present in firmware binary
> > + * @input_rt_size:  size of the resource table present in firmware binary
> > + * @output_rt:	    buffer to which the both static and dynamic resources will
> > + *		    be returned.
> > + * @output_rt_size: TrustZone expects caller should pass worst case size for
> > + *		    the output_rt.
> > + *
> > + * Return: 0 on success and nonzero on failure.
> > + *
> > + * Upon successful return, output_rt will have the resource table and output_rt_size
> > + * will have actual resource table size,
> > + */
> > +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);
> 
> I'd prefer the output buffer and size to be carried in a local variables
> until we determine success, to avoid overwriting the caller's size with
> some bogus number and return a pointer to freed memory.

Sure.

> 
> Wouldn't be unreasonable to return an ERR_PTR() with the allocated
> buffer, instead of returning through the reference.

We anyway have to return the size through reference, why not do the same for 
allocated buffer as well..


-- 
-Mukesh Ojha

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