On Tue, Sep 16, 2025 at 03:26:47PM +0200, Arnaud POULIQUEN wrote:

Hello Sumit,

On 9/16/25 11:14, Sumit Garg wrote:

quoted

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 :)

quoted

On Wed, Jun 25, 2025 at 11:40:26AM +0200, Arnaud Pouliquen wrote:

quoted

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/4b28bc79fdc552f3e0b870ef1362bb711925f4f3/dtschema/schemas/dt-core.yaml#L52

More details are available in the ST WIKI:
https://wiki.st.com/stm32mpu/wiki/OP-TEE_remoteproc_framework_overview#Device_tree_configuration
https://wiki.st.com/stm32mpu/wiki/Linux_remoteproc_framework_overview#Device_tree_configuration

quoted

quoted

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?

quoted

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