On Tue, Sep 16, 2025 at 03:26:47PM +0200, Arnaud POULIQUEN wrote:
Hello Sumit,
On 9/16/25 11:14, Sumit Garg wrote:
Hi Arnaud,
First of all apologies for such a late review comment as previously I wasn't CCed or involved in the review of this patch-set. In case any of my following comments have been discussed in the past then feel free to point me at relevant discussions.
No worries, there are too many versions of this series to follow all the past discussions. I sometimes have difficulty remembering all the discussions myself :)
On Wed, Jun 25, 2025 at 11:40:26AM +0200, Arnaud Pouliquen wrote:
The "st,stm32mp1-m4-tee" compatible is utilized in a system configuration where the Cortex-M4 firmware is loaded by the Trusted Execution Environment (TEE).
Having a DT based compatible for a TEE service to me just feels like it is redundant here. I can see you have also used a TEE bus based device too but that is not being properly used. I know subsystems like remoteproc, SCMI and others heavily rely on DT to hardcode properties of system firmware which are rather better to be discovered dynamically.
So I have an open question for you and the remoteproc subsystem maintainers being:
Is it feasible to rather leverage the benefits of a fully discoverable TEE bus rather than relying on platform bus/ DT to hardcode firmware properties?
The discoverable TEE bus does not works if the remoteproc is probed before the OP-TEE bus, in such case no possibility to know if the TEE TA is not yet available or not available at all. This point is mentioned in a comment in rproc_tee_register().
The reason here is that you are mixing platform and TEE bus for remoteproc driver. For probe, you rely on platform bus and then try to migrate to TEE bus via rproc_tee_register() is the problem here. Instead you should rather probe remoteproc device on TEE bus from the beginning.
Then, it is not only a firmware property in our case. Depending on the compatible string, we manage the hardware differently. The same compatibles are used in both OP-TEE and Linux. Based on the compatible, we can assign memories, clocks, and resets to either the secure or non-secure context. This approach is implemented on the STM32MP15 and STM32MP2x platforms.
You should have rather used the DT property "secure-status" [1] to say the remoteproc device is being managed by OP-TEE instead of Linux. Then the Linux driver will solely rely on TEE bus to have OP-TEE mediated remoteproc device.
[1] https://github.com/devicetree-org/dt-schema/blob/4b28bc79fdc552f3e0b870ef136...
More details are available in the ST WIKI: https://wiki.st.com/stm32mpu/wiki/OP-TEE_remoteproc_framework_overview#Devic... https://wiki.st.com/stm32mpu/wiki/Linux_remoteproc_framework_overview#Device...
For instance, this compatible is used in both the Linux and OP-TEE device trees:
- In OP-TEE, a node is defined in the device tree with the "st,stm32mp1-m4-tee" compatible to support signed remoteproc firmware. Based on DT properties, the OP-TEE remoteproc framework is initiated to expose a trusted application service to authenticate and load the remote processor firmware provided by the Linux remoteproc framework, as well as to start and stop the remote processor.
- In Linux, when the compatibility is set, the Cortex-M resets should not be declared in the device tree. In such a configuration, the reset is managed by the OP-TEE remoteproc driver and is no longer accessible from the Linux kernel.
Associated with this new compatible, add the "st,proc-id" property to identify the remote processor. This ID is used to define a unique ID, common between Linux, U-Boot, and OP-TEE, to identify a coprocessor.
This "st,proc-id" is just one such property which can rather be directly probed from the TEE/OP-TEE service rather than hardcoding it in DT here.
Do you mean a topology discovery mechanism through the TEE remoteproc service?
For the STM32MP15, it could work since we have only one remote processor. However, this is not the case for the STM32MP25, which embeds both a Cortex-M33 and a Cortex-M0.
I rather mean here whichever properties you can currently dicovering via DT can rather be discovered by invoke command taking property name as input and value as output.
Could you please elaborate on how you see the support of multiple remote processors without using an hardcoded identifier?
By multiple remote processors, do you mean there can be multiple combinations of which remote processor gets managed via OP-TEE or not?
I think the same will apply to other properties as well.
Could you details the other properties you have in mind?
I think the memory regions including the resource table can also be probed directly from the TEE service too. Is there any other DT property you rely upon when remoteproc is managed via OP-TEE?
-Sumit