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

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Message-ID: <0560bae7-f825-4bd4-bb9a-b7d145b0e621@oss.qualcomm.com>
Date: Wed, 17 Dec 2025 14:09:46 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        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 12/5/25 11:17 PM, Bjorn Andersson wrote:
> On Fri, Dec 05, 2025 at 02:15:00PM +0100, Konrad Dybcio wrote:
>> On 12/4/25 1:28 PM, Mukesh Ojha wrote:
>>> On Wed, Dec 03, 2025 at 01:36:32PM +0100, Konrad Dybcio wrote:
>>>> On 11/24/25 4:25 PM, Mukesh Ojha wrote:
>>>>> 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.
>>
>> [...]
>>
>>> Just to avoid iteration, are you suggesting that we can keep this
>>> guesswork as part of __qcom_scm_pas_get_rsc_table() and start with
>>> something smaller than SZ_16K?
>>>
>>> I kind of agree with the first part, but SZ_16K was the recommended size
>>> from the firmware for Lemans to start with, in order to pass the SMC
>>> successfully on the first try. However, the same size was failing for
>>> Glymur, and it required a second attempt with the correct size.
>>
>> It depends on the payload, which you're probably much more familiar with.
>> If 95% of them will be closer to e.g. 1K in size, it perhaps makes sense
>> to use up the additional few dozen cycles on our amazingly fast CPUs and
>> retry as necessary, instead of blindly reserving a whole bunch of memory.
>>
> 
> Those "few dozen cycles", is tasked with sending messages to RPMh for
> voting and unvoting the buses, then tzmem will hopefully hit the
> genpool, twice, and then radix updates, and then more genpool updated
> and more radix tree work. And then of course there's the one context
> switch to secure world.
> 
> If we don't have space in the genpool, we're going to grow
> dma_alloc_coherent, extend the genpool, call secure world to register
> the new tzmem. And then for all those cases where the allocation wasn't
> enough, the retry (with updated size) will not fit in the
> PAGE_ALIGN(size) genpool that was created, so we'll do this twice.
> 
> Fortunately the tzmem growing should only happen on first remoteproc
> boot, but I think it's a bit optimistic to say "a few dozen"...
> 
> 
> The drawback with making it 16KB is that we're not going to test that
> error path very often. But the more idiomatic form of first calling with
> a size of 0, then allocate and pass the proper size, seems a bit
> wasteful to me as well - in particular if we do it anew each subsystem
> boot.
> 
> PS. 16KB is 0.03% of the ADSP carveout (or 3% of the ADSP DeviceTree
> carveout...).

Hm, perhaps 16 is not a bad choice then

Konrad